Automatic LED Emergency Light-Modified Version

Hi All Readers of CircuitsToday,

As there is serious discussions going on about our previous Automatic LED Emergency Light Circuit using LM 317, Mr.Seetharaman has come up with a modified version of the same which answers many of the doubts raised in our Comments section.

Note: Mr.Seetharaman has developed a new version of Automatic LED emergency light. This one is more simple,more efficient and uses minimum components. Take a look: Simple Emergency Lamp Circuit

Here follows Seetharaman’s Description about the Modified Automatic LED Emergency Light using LM 317.

Dear John
Since there were lots of doubts from our readers on the LED emergency light, I have written a detailed letter to two of our readers. Of course few modifications are required, which I have indicated on the drawings and on calculations how I arrived at it.  I thought of enclosing it to you so that it can be kept in some library of our site for any ones reference. For each circuit we can have a similar detailed theory, may not be with all calculation, just general operation theory of each part of the circuit. You may think of it. As a first feed back I am sending this.  I have a feeling that most of the people would have made the mistake in base emitter of BD140, the lead out are against normal convention.

 

 

Automatic-LED-Emergency-Light-Modified

To understand the above circuit in a better way, it can be divided into two parts.

1. LED lamp circuit
2. The Battery charger circuit

LED Lamp circuit

1. All are white hi bright LEDs rated for 3Volt @ 25mA
2. The total current requirement is 12 X 25 = 300mA
3. This current has to flow through T2 – BD140 PNP transistor
4. The minimum current gain (hfe) of this transistor @ 500mA is 50
5. Hence the base current Ib requirement is Ic / hfe, 300 / 50 = 6mA
6. Base emitter drop of T2 at 500mA is 0.77 volt
7. With the fully charged battery at 6.9volt terminal voltage (for cycle operation use) the voltage available across the new bias resistance is (6.9 – 0.77)
8. Hence the bias resistance is = 6.13 / 6 = 1000ohms
9. As the battery drains the final terminal voltage will be 5.4volt
10. The bias resistance will be (5.4 – 0.77) /  6 = 770 ohms Hence a 680 ohms was preferred for bias resistance with drained battery also it will give enough brightness.
11. The very important information about BD140 is, as you view the pins, metal portion of the transistor facing down left is emitter centre collector and right is base. Most of the constructors make this mistake, relying on the convention that left base and right emitter. If you have made this mistake please correct it.

Once this portion is checked for reliable operation we will proceed to charger portion.

 

The Battery charger circuit

1. The battery requires a full terminal voltage of 6.9V at this point charger should cut off.
2. That is the voltage across the chain ZD1, R2 and T1 be should be 6.9 volt
3. T1 be voltage of 0.7 volt plus drop across R2 and zener voltage should be 6.9V
4. T1 be current = Ic / hfe
5. Ic is 1.25 / 180 = 7mA
6. Ibe = Ic / hfe of T1  i.e = 7 / 70 = 100uA
7. Drop across R2  =1.2 X .1 mA = 0.12volt
8. Hence Zener voltage = 6.9 – (0.7 + 0.12) = 6.08 the near by preferred zener voltage is 6.2 volt
9. Say the battery voltage at full charge will be 7 volt with 6.2 volt zener diode
10. To calculate R16 value for charging at 1 /10 th of the rated current of the battery 4.5AH / 10 = 450mAH
11. Transformer 9volt AC the voltage across C1 will be 9 X 1.414 = 12.6 volt
12. The drop across LM317 at 450mA current for good regulation is 3volt
13. The drop across protective diode D5 is 0.7 volt.
14. The  voltage available at cathode of D5 is 12.6 – (3+0.7) = 8.9volt
15. The battery after fair discharge will be at 6 volt
16. Hence R16 = (8.9 – 7) / 0.45 = 6 ohms
17. The nearby standard value for operation is 5 ohms.
18. At the end point of battery 5.4 volt the maximum charging current can be of (8.9 – 5.4) / 5 = 0.7 amps well within the higher charging limit of the battery.
19. With this circuit over night the battery will get charged fully.
20. Over charging is taken care and protected by T1

Hope with the above guide line you can make your light work successfully.

More Modification!!!

Automatic LED Emergency Light with Under Voltage Cut Off Protection:

Dear Readers,

Mr. Seetharaman has further modified this LED Emergency Light with an under voltage cut-off protection to protect battery from deep discharge. Once the battery terminal voltage falls below 5.7 volts the LEDs will be switched off. Take a look at the modified circuit shown below.

LED Emergency Light with Under Voltage Cut-Off Protection

 

To understand the above circuit in a better way, it can be divided into two parts.

    1. LED lamp circuit
    2. The Battery charger circuit

LED Lamp circuit

    1. All are white hi bright LEDs rated for 3Volt @ 25mA
    2. The total current requirement is 12 X 25 = 300mA
    3. This current has to flow through T2 – BD140 PNP transistor
    4. The minimum current gain (hfe) of this transistor @ 500mA is 50
    5. Hence the base current Ib requirement is Ic / hfe, 300 / 50 = 6mA
    6. Base emitter drop of T2 at 500mA is 0.77 volt
    7. With the fully charged battery at 6.9volt terminal voltage (for cycle operation use) the voltage available across the new bias resistance is (6.9 – 0.77)
    8. Hence the bias resistance is = 6.13 / 6 = 1000ohms
    9. As the battery drains the final terminal voltage will be 5.4volt
    10. The bias resistance will be (5.4 – 0.77) /  6 = 770 ohms Hence a 680 ohms was preferred for bias resistance with drained battery also it will give enough brightness.
    11. The very important information about BD140 is, as you view the pins, metal portion of the transistor facing down left is emitter centre collector and right is base. Most of the constructors make this mistake, relying on the convention that left base and right emitter. If you have made this mistake please correct it.
    Once this portion is checked for reliable operation we will proceed to charger portion.
  1. The battery requires a full terminal voltage of 6.9V at this point charger should cut off.
  2. That is the voltage across the chain ZD1, R2 and T1 be should be 6.9 volt
  3. T1 be voltage of 0.7 volt plus drop across R2 and zener voltage should be 6.9V
  4. T1 be current = Ic / hfe
  5. Ic is 1.25 / 180 = 7mA
  6. Ibe = Ic / hfe of T1  i.e = 7 / 70 = 100uA
  7. Drop across R2  =1.2 X .1 mA = 0.12volt
  8. Hence Zener voltage = 6.9 – (0.7 + 0.12) = 6.08 the near by preferred zener voltage is 6.2 volt
  9. Say the battery voltage at full charge will be 7 volt with 6.2 volt zener diode
  10. To calculate R16 value for charging at 1 /10 th of the rated current of the battery 4.5AH / 10 = 450mAH
  11. Transformer 9volt AC the voltage across C1 will be 9 X 1.414 = 12.6 volt
  12. The drop across LM317 at 450mA current for good regulation is 3volt
  13. The drop across protective diode D5 is 0.7 volt.
  14. The  voltage available at cathode of D5 is 12.6 – (3+0.7) = 8.9volt
  15. The battery after fair discharge will be at 6 volt
  16. Hence R16 = (8.9 – 7) / 0.45 = 6 ohms
  17. The nearby standard value for operation is 5 ohms.
  18. At the end point of battery 5.4 volt the maximum charging current can be of (8.9 – 5.4) / 5 = 0.7 amps well within the higher charging limit of the battery.
  19. With this circuit over night the battery will get charged fully.
  20. Over charging is taken care and protected by T1

Hope with the above guide line you can make your light work successfully.

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Leave a Reply

526 Responses to “Automatic LED Emergency Light-Modified Version”

  • Wycliffe says:

    Hi sir, could you please provide me with the separate operational theories of both the LED lamp and battery charger circuits? Thanks

  • faiz says:

    I do this project in my final project,but this project i has been modified to use 80 white led,,so what the component i need to change,,plizz help,

  • Skanda h r says:

    Wt s d value of R3 – R14?

  • Circuit not working says:

    dear Mr. seetharaman,

    thank you for your contribution. however this circuit is not functioning well. i have wired the connection exactly as mentioned in the circuit diagram. the problem is that the green led (charging/charging stop indicator) always glow and battery not charging beyond 6.40 volt. i am using 2 amps transformer but 0 current passes after 6.40 volts. according to you it should reach 6.9 and cut off. but green led does not turn off.

  • Naveen kunar says:

    sir i want use 12 volt 6ah lead acid battery. please tell me neccesary changes in charging circuit

  • april verdeflor says:

    i hope you will make a step by step video on how you make an automatic LED emergency light. it would be a great help for beginners like me. thank you. :)

  • alireza says:

    Hi, I am an Iranian and I am so glad that I met you guys.
    Your best and most complete website is in electronics education for children.

  • pranajit says:

    Sir,
    can you please upload the PCB for Automatic LED Emergency Light with Under Voltage Cut Off Protection circuit.
    Thanks

  • auto circuit giagram of emergency light

    • Seetharaman says:

      This is the auto circuit diagram when the mains supply is on the battery will get charged and when mains power fail the LEDs will turn on automatically.

  • D.Bashyam says:

    Hi,
    very interesting subjects and projects,keep it up.We find almost all circuits invariably has a transformer but designing such transformers are not provided. can you forward me with such reference or the data sheet for 10Va-100/200Va design.
    bashyam

  • TANMAY says:

    sir, 1. i did not understand that how the led near the potentiometer determines that battery is getting charged.
    2. i did not understand the fifth step in the battery charger circuit.

    • Seetharaman says:

      When the battery s charging the IC output voltage will be 6.9 or more depends on the current flow to battery. once the charge is full the terminal voltage will reach 6.9volt or more the T1 transistor will conduct to bypass the reference current through R1 180 ohms. the current through it is reference voltage between pin no 2 & 1 of the IC which 1.25 volt and the resistance is 180 ohms hence the current through R1 is 7mA. this is the current T1 to bypass hence in the next step what is the T1 base current required 7 ma / hfe of T1 which is 70 etc etc.

  • Vivek verma says:

    How to build this circuit using 50 LED’s?

  • hui wijaya says:

    hii. i ve just build this circuit with the absent of 4.7ohm near diode 1n4007 … and i need 7.47v at the output diode to cutoff voltage(led on the emitter and collector of bc548 to turn off) .. could we make it more low voltage needed to cutoff and where i m wrong?is the resistor 4.7 ohm missing so the circuit goes wrong?

    • Seetharaman says:

      Hi first disconnect over voltage protection circuit ZD1 R2 and T1. Now adjust VR1 for the required output voltage without connecting battery. The resistance 4.7 ohms is the charging current limiting resistance kindly do not delete. Now connect the battery and check the current flow to battery by measuring the voltage drop across 4.7 ohms. If you want higher charging current reduce the value to 2.2 ohms

  • lester musca says:

    How to write an circuit operation in this example and circuit application. Please help me to do this.. RIchard.

  • Vivek verma says:

    Modify the current version with new implementation like
    1.Touch dimmer circuit,
    2.Battery over charging protection,
    3.60 LED’s setup,
    4.Battery low indicator with buzzer.
    Sir,please consider my suggestion and upload the circuit for the same.

  • Vivek verma says:

    Hello sir, i have succeeded in making automatic emergency light using 12 LED’s but unsuccessful while using 50 LED’s, i kindly request you to help me out while making automatic emergency light using 50 LED’s. Please upload a circuit description of automatic emergency light using 50 LED’s.

  • Imron Zarkasyi says:

    I’ve succeeded with this circuit, but I still need one more modification on it. It is how to embed a night-activated function so that the LEDs are not glowing at the absence of mains power in the day light. Can you give me a brief explanation or a schematic of combining these circuits? thanks.

  • Seetharaman says:

    Please check the pin connections of LM317 it is not similar to 78XX series. and correct it it will become alright.

  • Assam Butt says:

    Assam Butt

    Dear Respected Seetharam,

    i have been working on this circuit since two weeks and facing only one problem again and again,

    1. the charging circuit is not working properly, as LM317 is not giving regulated voltage, if i disconnect the circuit right after the LM317, it shows a potential difference of 8~9v DC between gnd and output pin of regulator(not stable). if i remove the Resistor R1 and then measure the voltage across ZD1 it gives me 6.2V DC. furthermore, i think in my circuit T1 is not switching with R1(180ohm) i replaced the resistor with a variable resistance and then tried to adjust it with circuit “ON”
    at an instance when it reached only 10ohm circuit led’s started to glow fully. at that time i measured the voltage across ZD1 and adjusted with VR1 at 6.9v DC (without battery connected).
    but after some seconds i felt smell and then VR1 gave a flash and gone bad.
    Please guide me should i change any resistor value or put exactly the same components?
    secondly, we cannot get the transistor of same hfe from market do it have any effect on the circuit or resistor?
    Kindly Help me out from this scenario.
    Thanks and Regards,

  • Yumna says:

    Dear Sir
    I have made this circuit i am not getting 3volts at the output of LM317 this way the battery wont charge. Please help me!

  • Yumna says:

    Hello Sir,
    What changes will I have to do in the circuit if i want to use 4.8V 2.7Ah rechargeable battery? Please help! Thank you.

  • nikita says:

    Sir,Is transformer used for charging purpose in Automatic LED Emergency Light?

  • Arun kumar says:

    iam not charging in battery. disconnected the battery check out voltage 6.2
    in circuit please help me…….

  • Arun kumar says:

    iam this circuit ready iam connected battery not charging.

  • Sachin says:

    Sir this ckt not working plz help me i selected this for hobby project

  • Andy says:

    Hi Seetharaman.

    I try to make this under voltage cutoff circuit. But it don’t work.
    Try to replace 5.1v to 5.6v zener, BC547 to BC337, 560R resistor to 1k…etc…still does not work.

    With extra under voltage cut-off protection circuit, when I plugging the power source, the light will not turn off, when battery discharge down to 5.1v, lights not cut-off. I think this extra circuit will never work.

    You’ve ever tried to make this circuit yet?

    • seetharaman says:

      Hi Andy it is tried practically. with higher gain pnp transistor for BD140 similar to S8550 I ahd a problem of light glowing low with mains on hence R15 was reduced to 330 ohms. otherwise it is working fine at my home.

      • Andy says:

        Hi seetharaman.
        Reduce R15 down to 330R is working, thanks for help.
        But cut-off protection dont work, any suggestion ?

  • Arpan says:

    I have wired the “Automatic LED Emergency Light with Under Voltage Cut Off Protection” circuit .I used 15v transformer.I removed the led which indicates charging. but when the value of VR1 is kept at the highest i only get a voltage drop of 6.5v between gnd. if I use 6.5 volts to charge this battery, will battery ever reach 6.9V which is higher than reacharging voltage?I found that the battery has never been fully charged, furthermore the maximum output voltage is only 6.5v (battery disconnected).I tried to replace the D1 with the new ones many times but it still showed the same thing. I even replaced the T1 BC548 but nothing changed.what should i do?

    • Seetharaman says:

      Hi Arpan replace VR1 with 4.7K. by disconnecting battery and T1 chech and set the output voltage to 6.9 volts with VR1. Then connect battery etc.

      • Arpan says:

        Then how it protect the battery from overcharge if I remove T1 .I also used 4.7k and more but the output voltage is not exceed 6.5v in presence of zener diode.

        • seetharaman says:

          For protecting the battery constant voltage is important plus the maximum current. current is taken care by IC charecterestic itself will limit to 1.5A max. the voltage by VR1 which sets the the output voltage to 6.9volt. the zener is only a backup protection in the event of potentiometer failure over a period of time.

    • Andy says:

      Arpan.
      Try replace R1 180R to 120R.

  • chinmay says:

    how to give heat sink to LM317 and BD140 and have u tried this circuit… ??

  • Zildjian says:

    Hi sir, i need help. the led indicator wont light. it only lights when i remove the battery from the circuit. one more thing i dont think that my battery is charging cause i only get 5.8v in the battery terminal without the battery.

    please reply..
    many thanks

    • Seetharaman says:

      HI Zild you kindly check the 317 output voltage with LED indication and also without it. without LED if it becomes OK, replace LED with high efficiency 3mm red LED which requires only 2 to 3mA for brightness.

  • siri says:

    6v 4.5ah means?

    • Seetharaman says:

      Hi Siri 6volt is the battery terminal potential difference.(the voltage available for your use). mAH is ampere hour rating of the battery. in simpler words 4.5 AH 20 hours rating means, If you discharge at a current rating of 225mA the battery will sully the load for 20hours. For easy under standing, it is the product of the current the battery can supply in Amps for so many hours. If you draw 450mA from a fully charged battery, it will supply this current for 10hrs approximately. please go through the following link.
      http://www.dcbattery.com/faq.html

  • saad khurram says:

    Hello sir
    I too have a requirement to modify this circuit to work with a 12v 7AH battery. What modification is required to drive a 1W single or double LED?

    regds
    saad

    • abhi says:

      hi sir
      i made the circuit for 9v dc battery and have changed the zener diode D1 to 9v and D2 to 8v
      but it doesn’t work so what all modification do i need
      plz help

      i need modification for 9v dc battery what all things do i need to change

      • Andy says:

        Hi abhi.
        What type your 9V battery ? yr battery is Nicad, NiMH, Lion or sealed lead acid ?
        Remember, this circuit is only used with sealed lead acid battery.

    • Andy says:

      Hi saad khurram.

      To charge 12v battery, V charge=13.8V, the power source at least: 13.8v+3v+0.7v=17.5v, choose 18v source minimum.

      ZD1= 13.8v-(0.7+0.12)= 12.98v, choose 1N4743A 13v zener.

      To calculate R16 value for charging at 1/10th of the rated current of the battery 7AH/10=0.7AH. Because voltage reference of LM317 is Vout-Vadj=1.25v, R16=(1.25+0.7)/0.7=2.78R, choose 2.7ohm 5w resistor.

      For safety discharge battery under 10v, choose ZD2=10v zener 1N4740A.

      Depend what type of Led, u can use formula to calcutale resistor limit: R=(Vbattery – Vled)/Aled, example if ur led working with 5v/50mA: 12v-5v/0.05=140ohm.

  • Rohit says:

    Sir, if we use 6.2 volts to charge this battery even with over charging, will battery ever reach 6.9V which is higher than reacharging voltage?

  • Amit Sharma says:

    Dear Sir,
    Can this circuit be modified for 20-24W, using 12V-7.5AH battery.
    what modifications are required when we use 3W or 5W power leds.
    I need it for my farm at my village place, as we have 14 hrs of power cut daily.

  • bashir ahmad says:

    Dear Brother, i first disconnect ZD1 and set the required voltage correctly 6.999v through POT as desired. then i reconnect the Zener ZD1 and desired voltage remain the same. But i am facing LOW CURRENT FLOW issue, when i omitt the diode D5 the current flows as desired but when i connect D5 the current the reduces to only 20mA and at that time the voltage of the battery is 6.2v, i aslo changed D5 (i.e 1N4007) but all in vain. At such stage the current flow should be atleast 100mA which is not the case. Please sir, make me correct i am making a mistake somewhere in the circuit…..Thanks….Regard

  • Linnet says:

    Hi sir,urgently want keil codes for developing a color-panel on touchscreen LCD. Im using ARM7 LPC2148 processor.

    Pls reply soon!
    Thanks!

  • RAJIB BANERJEE says:

    Respected ,Seetharaman Sir,
    I need a good circuit witch will fit any Regular Inverter from outside as a device,and this will working as a hybrid solar inverter, will function as a junction box of the solar pannel unit for charing the existing batery of that inverter and if not charging from solar properly then convert the charging line to the ac mains for full charge of that battery.
    If this possible,then send my mail,Thanks.Rajib

  • Assam Butt says:

    Assam Butt
    Your comment is awaiting moderation.
    January 10, 2013 at 10:04 pm

    Dear Respected Seetharam,

    i have been working on this circuit since two weeks and facing only one problem again and again,

    1. the charging circuit is not working properly, as LM317 is not giving regulated voltage, if i disconnect the circuit right after the LM317, it shows a potential difference of 8~9v DC between gnd and output pin of regulator(not stable). if i remove the Resistor R1 and then measure the voltage across ZD1 it gives me 6.2V DC. furthermore, i think in my circuit T1 is not switching with R1(180ohm) i replaced the resistor with a variable resistance and then tried to adjust it with circuit “ON”
    at an instance when it reached only 10ohm circuit led’s started to glow fully. at that time i measured the voltage across ZD1 and adjusted with VR1 at 6.9v DC (without battery connected).
    but after some seconds i felt smell and then VR1 gave a flash and gone bad.
    Please guide me should i change any resistor value or put exactly the same components?
    secondly, we cannot get the transistor of same hfe from market do it have any effect on the circuit or resistor?
    Kindly Help me out from this scenario.
    Thanks and Regards,

  • Vivek says:

    Dear Seetharaman Sir

    Firstly, i would like to extend my sincere appreciation for the wonderful work that you and this site are doing.

    I want to manufacture a few complex circuit for use at home and would like to know how i can contact you personally. I have a flow diagram and know how the system should function but i do not know how to bring it into practical use since i am not strong in electronics. I would really appreciate a mail from you in this regard. Thank you in advance

  • [...] 3. Modified Version of Automatic LED Emergency Lamp using LM 317 [...]

  • dilip says:

    how we can convert 7v to 1.5v?

  • SISON says:

    respected sir,
    AFTER SHOWERING OF TOO MUCH COMMENTS NEED ITS TIME TO MODIFIED
    YOUR CIRCUIT AGAIN.BCZ ITS DIFFICULT TO READ 400 COMMENTS.ALSO I WOULD LIKE TO NOTE THAT EVEN AFTER 4 VOLT IN BATTERY STILL DEEP DISCHARGE NOT WORKING.ALSO BATTERY TERMINAL VOLTAGE NEVER REACH ATLEAST 6.9V.

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  • please send the details of the topic ANTI-PETROL THEFT ALARM .YOUR SITE IS PROVIDING A LOT OF HELP TO US

  • Biju says:

    Sir,
    I have one doubt about the battery charger part of the circuit. Is it possible to get 400mA at 8V considering the diode D5 forward resistance of few hundred ohms added to circuit?(I’m getting only 40mA at the output at 8V)
    At my place the supply voltage is about 170 to 190 V during most of the times, so do i need to change the transformer?

    • Seetharaman says:

      Hi Biju use a 12 volt transformer, this should take care and use a good heat sink for LM317 regulator IC.

  • Assam Butt says:

    Dear Respected Seetharam,

    i have been working on this circuit since two weeks and facing only one problem again and again,

    1. the charging circuit is not working properly, as LM317 is not giving regulated voltage, if i disconnect the circuit right after the LM317, it shows a potential difference of 8~9v DC between gnd and output pin of regulator(not stable). if i remove the Resistor R1 and then measure the voltage across ZD1 it gives me 6.2V DC. furthermore, i think in my circuit T1 is not switching with R1(180ohm) i replaced the resistor with a variable resistance and then tried to adjust it with circuit “ON”
    at an instance when it reached only 10ohm circuit led’s started to glow fully. at that time i measured the voltage across ZD1 and adjusted with VR1 at 6.9v DC (without battery connected).
    but after some seconds i felt smell and then VR1 gave a flash and gone bad.
    Please guide me should i change any resistor value or put exactly the same components?
    secondly, we cannot get the transistor of same hfe from market do it have any effect on the circuit or resistor?
    Kindly Help me out from this scenario.
    Thanks and Regards,

  • surbhi says:

    sir,what are the basic requirements for implimenting this circuit.i just want to know “how to start” and what are the basic electronics kit requirement????????????

  • Imron says:

    I found that the battery has never been fully charged, furthermore the maximum output voltage is only 6.4v (battery disconnected). When I took out the T1 BC548, the output voltage was 9v. As you said, in the previous comments, that it’s due to the defected D1 zener 6.2v 0.5w. I tried to replace the D1 with the new ones many times but it still showed the same thing. I even replaced the T1 BC548 but nothing changed.
    I also need to know how many sets (BD140+12 LEDs) can be supplied by this circuit? Can I use 5 or 6 sets?

    Look forward to your reply soon. Thanks.

    • Seetharaman says:

      Hi Imron use a 6.8 volt zener. With 5 sets the battery charge will last for 2 to 2 1/2 hrs. with 6 sets it will last for around 1 1/2 to 2 hrs.

  • Imron says:

    Thanks for the circuit. I’ve tried it and it worked perfectly. But there is something I don’t understand, It’s how to adjust the VR1. The red LED glows all the time and I’m just worried that the battery is over charged. Would you please give me a brief explanation on how to correctly adjust the VR1 so that I am sure that the battery is not charged all the time but stops when it’s already fully charged. Thanks.

  • vignesh says:

    whether collector of t2 is connected to battery or emitter…..thank you i advance isr

  • sibi says:

    Hi

    Can we use PWM circuit using 555 to extend the working time?
    So the LED wont be on all the time, but due to persistence of vision we can see continuous light.How much improvement can we expect with that?

  • Deepak says:

    Mr.Seetharaman, your circuit is really good. Can you help me in modifying the circuit, so that we can add two more led lights in series to all the leds. This will result in high power light output. Pls reply to mail with the circuit. Thanks.

  • vignesh says:

    respected sir
    i wish to know how the transistor ll cut off the battery charging when it exceeds 6.9v…..thank you in advance

  • Jotham says:

    hello, sir. I have a 12v 12ah Battery and i want to use “12v 10w rounded Fluorescent tube”…( like car’s ones )
    i need 2 link 3 pieces of this Fluorescent tube.
    so, i want 2 know the new modifications for that circuit which are related to :
    1-the suitable Transformer (volt and ampere)
    2-ZDs (volts and watts)
    3-BD140
    4-LM317
    5-the other components.
    6-for how many hours will the lighting keep on in full-charging case ?

  • Jotham says:

    hello, sir. I have a 12v 12ah Battery…what if i want to use a “12v 10w rounded fluorescent (like cars’ ones)”
    i will link about 3 pieces of this fluorescent type..
    what modifications should i perform on
    1-Transformer
    2-ZDs
    3-BD140
    4-LM317
    5-other components.
    and for how many hours will it keep ON lighting in full charging case?
    Regards,

  • Rajib Chowdhury says:

    Respected Sir,
    I want to add one more feature to your circuit, the leds should be controlled with an ir remote,how can I make such a modification to your circuit ? If possible please refer some websites from where I can perform these modifications.
    Thank you.

  • Muthukrishnan says:

    Respected sir,
    I was tried so many times sir,but battery discharging circuit not working sir i used 5.1 v znr but below 4 volt also led continuously glowing sir…i checked the component everything correct.but deep discharging not function sir.automatically switching and every thing is good sir next what can i do please explain me sir my mail id Krishna198023@gmail.com Help me sir.

    thank you

  • joshua keen says:

    hi sir seetharaman

    im currently using ur circuit here but cant seem to find a way to make it work, i modified it with my own specification… heres what i modified recently…

    -instead of 12 led i used 24 leds
    -replaced the battery to 12v with 7.2ah ( supposed to be 7.5ah but cant seem to find one in our place)

    sir i tried using ur original circuit in multisim v11 but the LED indicator for charging doesnt work.. i also tried to put a voltmeter in parallel to the battery to see if its charging but seems to me that its not

    with ur current skills maybe u could put me in the right direction, thank you very much for ur help

  • angelie says:

    hello sir…can i ask for complete information about this topic for my project sir?

  • Shankar Varma says:

    the voltage across the cathode of ZD1 and gnd is only 6.4V. when i removed the battery and the zener ZD1 and made the voltage at the charging poing of the battery(which was the junction of ZD1 and 4.7 ohm ) as 7v. the voltage drops when i connect the zener and also the ZD1 is not conducting.

    • seetharaman says:

      Hi Shankar You disconnect ZD1 and battery. now measuring the output voltage going to battery for charging. set it for 6.9 volt DC now connect the battery check the voltage drop across R16 and calculate the current flowing with a flat battery it should be 500mA and partially charged battery it can be between 50 and 250mA. If this current is not available your LM317 pin connections are wrong or your transformer is not capable of 9 volt RMS at 500mA. check throughly. this is a proven circuit design.

  • Shankar Varma says:

    i also checked the voltage across zener when it is reverse biased , it is 6.2v. and the zener diode also works when connected to a 9v battery with 1k in series and in reverse bias , giving a voltage 0f 6.2v across it. i also checked the R1 and pot resistance. i have been trying this for many days now. please help.

  • Shankar Varma says:

    i did wire the circuit exactly as in figure. i find out that the zener is not concucting and the voltage over the zener changes when the value of VR1 is changed(when battery not connected).i have not connected the battery.and the potential difference with respect to the gnd at the cathode of zener, zd1 is max 0f 6.9 . when i remove the transistor T1 the output of LM317 is raised till 9v. I tried changing zener diode(6.2v 0.5w)many times but it does not get corrected.i also tried changing BC548, and LM317 . still i have the same problem. i find out that zd1 is not conducting in reverse bias when the battery is not connected.PLEASE HELP…PLEASE.. :(

  • Shankar Varma says:

    i have wired the “Automatic LED Emergency Light with Under Voltage Cut Off Protection” circuit . the led which indicates charging has been glowing for more than 20 hours.. i dont know till what value the lm317′s output is to be adjusted. but when the value of VR1 is kept at the highest i only get a voltage drop of 6.64v betewwn gnd. what should i do?

  • Vijay says:

    Dear Mr Seetharaman,

    I need to design a display using 5×7 matrix LED with certain light output specifications for commercial purpose. Can i contact you directly at your email id for assistance, if yes, give me your email id.

    Vijay
    vijaybhise@hotmail.com

  • Isaac says:

    sir i have build a charging circuit that uses a BD 140 transistor to charge a 4.8 NiCd battery. Can i please know the operation of this transistor and also how can i calculate the taken for my battery to be fully charged and the time it will last when used. Thanks.

  • Ahsan says:

    i have tried this circuit with 2 1watt led in series and kept all the same but i have a problem that when the circuit is powered by battery it feedback some of voltage to regulator in my case nearly 5 volt and charging led lights. what should i am doing wrong any suggestion to me

  • Seetharaman says:

    Hi Srikanth add one more BD140 and 12 more LEDs with resistances
    Hi Aswin you can use BD136 or BD138 or the present 8550

  • Aswin Jose says:

    hey
    I dont have BD140 available in stores… But BD136 is available… Any changes if i use that???

  • min says:

    hello mr.seeetharaman..this circuit design is very helpful for me..could u pls help me in making the same circuit but with more number of LEDs which is bright enough like a CFL lamp..is that possible? if so do i need to change any other component as well for this change? do pls help..
    thank you very much..

  • Srikanth says:

    Sir,ur modified version of LED circuit working very well.I need to install atleast 24 nos LED.what are the changes in the value of other components..?

  • Seetharaman says:

    Hi Philips. Use 3nos AA rechargeable cells with limiting resistance per LED. or use a driver capable of 3.2 volts for an input of 2.2 to 2,64 volts. use a simple capacitance-rectifier-resistance charger circuit direct from mains for 1/12 of rated current of the cell.

  • Philip Joy says:

    hi the emergency lamp is working great- i now plan to make a rechargeable LED head lamp- it doesn’t need to be automatic- i intend to use a 3 volt hi bright LED and 2 AA size rechargeable cells to keep it light- it just need voltage regulation and over charge cut off- can you please help me sir?

  • Siva Kumar says:

    Dear Sir,
    I have doubt sir. can i use the circuit for 30 LED’s parallel connection.
    otherwise is there any changes required sir.what is the current gain for LM317.

  • Sreejith Pillai says:

    Thank You Sir.

  • Seetharaman says:

    Hi Pillai CFL requires around 110 volts at high frequency. If you want to convert it into an LED emergency light, except the battery and the switch remove all the other electronics available inside. replace them with the new assembled LED PCB. I prefer you to try the simple one appeared earlier use the following link.
    http://www.circuitstoday.com/automatic-led-emergency-light#simple

  • Sreejith Pillai says:

    Dear Sir,

    I have a working emergency cfl lamp.Can I replace the CFL lamp with say 10-20 leds? What are the required circuit modification for the same.From where should I tap the supply for the LEDs.Also how much voltage does a CFL require for working??

  • Philip Joy says:

    Thank You!!- PCB designed and fabricated- Going to assemble tomorrow !!

  • Seetharaman says:

    Hi use 2 in series and 3 of then in parallel it will be 900mA drain on the battery you will get around 5hrs of non stop lighting from a fully charged battery. (4500mAH / 900mA = 5H) Similarly you can calculate for other loads

  • Setharaman says:

    Hi Philipif you use 2 in series and 3 of then in parallel it will be 900mA drain on the battery you will get around 5hrs of non stop lighting from a fully charged battery. (4500mAH / 900mA = 5H) Similarly you can calculate for other loads

  • jamshed says:

    Dear Sir,

    This relates to Fridge Door Alarm circuit and need your support as there might be no response at message sent at url of said circuit.

    I have constructed above project on zero board and chekced all connections but used 22uf as 10uf was not available with me. circuit produces a very little sound and not a BEEP! no affect observed when LDR is brought to dark or light, pl help in finding error.

    i also want to know, why a high value R3 (2.2M) and R4 (1M) are used, is it the reason??
    thanks.

  • Philip Joy says:

    Sir, i forgot to ask max how many 300mA led’s can be connected in parallel? ie what is the max allowable current consumption?

  • Sreejith Pillai says:

    Dear Sir,

    I have a working emergency cfl lamp.Can I replace the CFL lamp with say 10-20 leds? What are the required circuit modification for the same.From where should I tap the supply for the LEDs.Also how much voltage does the CFL require for working??

  • Pratima says:

    hey seetharaman i need the design and calculations of the battery charger circuit using scr..mine is a 12v,1.3Ah battery.
    plz do help with the modifications also

  • seetharaman says:

    Hi Philip you can use, it will be a good power saver as no resistance is involved.

  • Philip Joy says:

    Sir, can we use 1 watt power LED’s for this circuit?
    Forward Voltage:3.2V – 3.6V
    Forward Current:300 mA

    can we use two such LED’s series instead of LED and a resistor?

  • seetharaman says:

    Hi John if you are using 12 volt transformer. the DC will be 17volt battery requirement is 7volt a drop of 10 volt at 1amp is 10watts dissipation on LM317. you have to use a good heat sink. regarding 4.7 ohms resistance at 1amp it will generate 5 watts approximate hence you have to raise the rating to 10 watts. first set the output voltage without connecting to battery for 6.9 to 7.2volt then connect battery things should become alright.

    • bilal says:

      sir, i have problem in my emergency light charging power supply its only give 3.85 volts to battery what the problem sir i made 3 emergency light same circuit diagram but problem appeared in power supply its only give 3 to4 volts only i am thankful to you sir please reply regard to?

      • Seetharaman says:

        Hi Bilal By disconnecting T1 and charge indicating LED check regulator output voltage it should be 7volt if not check regulator IC pin connection it is not similar to 78XX series ICs. please refer to IC manual and connect , it should become alright. still if you have problem check the wiring fully. it is a proven circuit it should work ok.

  • john says:

    i use 12v amd 1amp transformer so the resistor of 5w getting hot .what is the changing required?
    and what is the use of zener in this circuit…????? waiting for your reply…….

  • Seetharaman says:

    Alex kindly replace with 9 volt 1 amp good quality transformer.

  • avinash says:

    sir plz send on my gmail ID -full circuit of 40 watt inverter circuit with all information like, restance watt,tranformer coling volt,inductor etc plz telk me reply on my ID plz plz sir

  • Alex says:

    Hi,
    I made the circuit and its working fine but,the transformer is getting hot.ie;i cannot hold my finger on transformer not more than 5 seconds.Is it the fault with transformer or the circuit?Please help

  • Seetharaman says:

    Hi John please go through all the 400 responses you will get all your questions answered.

  • john says:

    i have many question regarding this led light
    Q1:why we use zenor diode?
    Q2:what is the use of bc548?
    Q3:can we use diode bridge in this circuit?
    Q4:how much leds will be connected in this circuit?
    i m wating for your ans thanks………

    • Q1. Ans: Zener diode is a active semiconductor device which has a heavily doped junction. It is always connected in reverse bias mode. It’s used to maintain a fixed voltage across, or in simple words, the zener diode is used to regulate voltage.

      Q2. Ans: BC 548 is a npn transistor. It’s used in the circuit to regulate the charging of the battery along with the zener diode.

      Q3. Ans: Yes you can use a i Amp bridge, or you can make a bridge using four IN4007 diodes.The scenario changes in case of implementation of center-taped transformer.

      Q4. Ans: built another array of led’s with limiting resistors and use a driver transistor BD 140 !!!

      Regards
      Shiharan Choudhury
      (R.F Engineer/professional electronic repairer)

  • Seetharaman says:

    Hi Davis no changes are required please proceed.

  • Davis says:

    Sir,will there be any difference if i use a 6v 10Ah battery in the same circuit?

  • Seetharaman says:

    Hi Shreyash when main supply is off it has to glow it is correct operation for the automatic emergency lamp. For your charging LED problem please refer my comments dated 13th April

  • Shreyash says:

    Sir,thank you for the circuit.But the problem for me is that when the main supply is off,the led’s still glow with the charging led still on.Help me out sir.I have to show this circuit tomorrow as my project

    • Hi, charging LED can’t be on when mains is off. This is because, if you see the circuit, you will find that there is a diode D5 (IN4007) which is forward biased when mains is on, and acts as reverse biased when on battery. i guess your diode might be leaky. Please check it using an analog or digital multimeter. And to control the automated illumination use the switch !!!

      Regards
      Shiharan Choudhury
      (RF engineer/ Professional electronic repairer)

  • Shreyash says:

    Sir,thank you for the circuit.But the problem for me is that when the main supply is off,the led’s still glow with the charging led still on.Help me out sir.I have to show this circuit tomorrow as my project

  • Abn says:

    hi,
    I couldn’t find 2.2K pot.can i bypass/modify it?

  • Seetharaman says:

    Hi Bashir it looks like your LM317 is a faulty one, replace it with a reputed make from standard supplier. if you feel your present circuit is ok in all respects except the faint glow in charging Diode add a Zener diode of 3.3 volts 1/2 watt in series with the LED which should solve your prolem.

  • bashir ahmad says:

    Dear sir when main power supply is OFF, and the circuit is connected to the battery the CHARGING LED still glows. but when i disconnect i the wire that is connected from T2 base to the D1 (of rectifier) the CHARGING LED becomes OFF but as well the main LEDs ARRAY also become OFF. i am using transistor 8550 for T3, also T3 becomes hot. plz help in correcting my mistake, so that CHARGING LED does not glow and LEDs array remains ON when circuit is connected to battery and main power supply is OFF. Please help me sir, my circuit is almost final just facing this problem……..plz help. plz reply……….

  • bashir ahmad says:

    dear sir, the ON/OFF switch as shown schematic is creating the problem. when the switch is ON then when main supply if absent and circuit is connected to the battery the CHARGIND LED GLOWS which should not be. But when i OFF the switch then the CHARGING LED does not glow and the circuit operates perfectly. but this switch has be kept ON as whenever main power supply become unavailabe the Lighting LEDs should then go ON. so where i have done mistake that by keeping the ON/OFF switch ON the current flows in such away that the CHARGING LED glows back from the battery even main power supply is off. plz reply in detail…

  • bashir ahmad says:

    dear sir, my ZD5 is not getting reverse biased and hence the current flows from the battery, in a result the CHARGING LED (RED) does not go off even in absence of main supply. please help in this regard.

  • seetharaman says:

    Hi Bashir once the supply is off for glowing the LED should get the supply from the battery, which is not possible as D5 will get reversed biased, hence no current can flow.

  • bashir ahmad says:

    dear sir, i am really thankful to you for your kindness, brilliant support and knowledge sharing attitude especially for people like me who are beginner to electronics.
    sir, my issue of current flow to the battery has resolved by correcting pin configurations of lm317. but sir if you dont mind, i want to ask one more question. i.e. every thing is working perfectly but sir when main power supply is off, the CHARGING LED INDICATOR still glow, while it should be off as at that time main supply is off. sir, kindly reply why it is behaving like this…thanks once again dear sir for your tremendous support.

  • seetharaman says:

    Hi Bashir check LM317 for pin connections. This circuit has to work and working. kindly consult any one of your nearby experts for the probable mistakes in your assembly.

  • bashir ahmad says:

    dear sir, i have removed T1, and then checked the flow of current to the battery and issuse is still there, the current flowing is still at 1mA. ( i have used correctly 4.7 ohm sir, and have thoroughly checked each and every component as per required specification). sir i have also removed ZD1, but it also did not solve my current issue. i once again installled the component on breadboard, (all new components) but the issue is still there even in the new circuit on breadboard, sir. i am completely confused sir at this stage what to do becasue i have checked all the possibilities………plz sir reply in detail and help me out of this problem…….

  • seetharaman says:

    Hi Bashir remove T1 and check for the current flow to battery, what is the value you have used for R16 is it 4.7 ohms or 4.7 kilo ohms.

  • Manjit Singh says:

    Dear Sir,
    I have same problem. I drained the battery to 5.8v, But current that flows to battery is 1mA.

  • bashir ahmad says:

    sir i have discconnected T1, but the current does not raised to its desired position, also i have changed my transformer from 12v @1A to correct specified one i.e 9v @500mA. but the issue of the low current flow to the battery and voltage drop still remains there. (i have the C6V2 5t written on ZD1..plz check it). Also sir when the main source is disconnected the current and voltage that flows to the load is perfectly all right. but i am amazed that why there is low flow of current to the battery instead the battery is drained properly as you said. sir, i am also doubtfull if the T1, T2, and T3 are soldered other way round, but may be its not true as the current from the battery flows perfectly fine to the load. please explain in detail so that i can overcome the issue…

  • bashir ahmad says:

    you mean sir if i disconnect T1, and the current comes back to the desired position, then i should change the ZD1. (my ZD1 is C6V2 5t written on it) or should i change the T1. please explain a little bit more in detail. so that i can act accordingly.
    Also sir i am really thanful to quick response and you are really helping alot of people.

  • seetharaman says:

    Hi Bashir disconnect T1 and try if it becomes alright check ZD1 voltage.

  • bashir ahmad says:

    dear sir, i drain the battery from 6.6v to 6.0v for almost 45 mintues more than you said, but the current issues still exisists there and the current that flows to the battery is on 3mA. do you think that its some other problem. i should i drain more the battery say to 5v etc. plz reply…

  • Seetharaman says:

    Hi Bashir please drain the battery with a load of 1amp for 30mts and try the charging current it will increase. a fullt topped up battery cannot consume any current, hence only a very small tricle current will flow.

  • bashir ahmad says:

    dear sir thank alot for reply, yes sir i have installed a good heat sink the voltage has become stable at 6.9v but i am facing current issue i.e the current that flows to the battery is only 1mA and not 450mA as you mentioned. how to resolve the current issue.

  • Seetharaman says:

    Hi Bashir you have to raise the voltge output to 6.9 to 7 volt. a fully charged battery terminal voltage will raise to 6.9 to 7.2 volts. Check whether the heat sink of LM317 voltage regulator is adequate if not use a good heat sink to reduce its dissipation once the IC getting heated up the output will fall down due to it’s built in thermal protection acting, hence a very good heat sinl for LM317 is a must.

  • bashir ahmad says:

    sir i am using 12v@1A transformer, i have assembled the circuit correctly and throughly checked each component. the voltage to the battery is set to 6.4v but there is a current issue. the current that flows to the battery is very limited and its only 3mA and i think the battery requires about 450mA and above. sir why current is so much less, 3mA is no thing for charging 6v 4.5Ah battery, although my battery is brand new. i have also checked it with another battery but the issue remains the same. sir plz reply me where i have done the mistake.

  • bashir ahmad says:

    dear sir, i have set the voltage in open circuit without connectiong the battery to 6.9v using 4.7k pot but while monitoring the voltage on digital multimeter, the voltage slowly goes down and reached to about 6.4v to 6.5v. i mean the voltage as you have mentioned should be set to 6.9v which i did, but it is not static and doesnot remain its position but rather it slowly goes down. sir plz reply me what mistake i have done.

  • bashir ahmad says:

    Dear sir, i have assembled the circuit and have over come my mistakes, but i am still facing one problem that the charging stops at 6.6v, also when i disconnect the main supply the LEDs comes on automatically but with a little delay, say a second. please comment.

  • bashir ahmad says:

    dear sir, i really appreciate your brilliant efforts and your support for the readers, especially for those who are new to electronics as i am. i have assembled the circuit as mentioned but i have some problems.
    1) first i have adjusted the pot 4.7k and its perfectly set to 6.9v in an open circuit but when i connect the battery and measure the current then its not 450mA while charging battery, and the current passed is about 19mA approximately. why?
    2) i connected a fully charged battery from some other source with the same specification to my circuit and tried to check the volatge at T3 but it is not passing the voltage and shows zero voltage on the meter, why?

  • Lan says:

    Thanks for your reply Sir. Another questions if you may, What is the purpose of BC548 transistor and how did you compute for the base resistance value 1200 ohms? Suppose I would change it to a different value, will it affect the circuit’s performance?

    I’m sorry if I am asking too many questions.

    Thank you so much in advance.

  • Seetharaman says:

    Hi Ansari raise transformer current rating to 2Amps (9Volt 18VA)and replace R16 with 1ohm 5watts and LM317 with LM338. This will take care of your requirement.

  • Seetharaman says:

    Hi Lan the gain spread for BD140 is given clearely in Philips component data book. Th gain curve with respect to collector currnt is also given, you can interapolate the curve. With the sample used the gain may vary due to the tolerance of the components used. I have given clearly it is the minimum guaranteed gain. in practice it may be more than that, which will not affect the performance of the circuit.

  • Dear Mr. Seetharaman:I am a non technical man. Your circuit “Modified Automatic LED Emergency Light using LM317″ is is a very good circuit, I like it, but charging time overnight is much,can you help me, if charging be completed within 5 hours please. email id akansari@gmail.com
    I will be very thankful, if replied please.

  • Dear Mr. Seetharaman:I am a non technical man. Your circuit “Modified Automatic LED Emergency Light using LM317″ is is a very good circuit, I like it, but charging time overnight is much,can you help me, if charging be completed within 5 hours please.

  • Lan says:

    Good day Sir!I’m just wondering how did you get the hfe value of 50 @ 500 ma from the BD140 transistor. I have the specification sheet but I can’t figure out how did you come up with the mentioned values. Thanks.

  • Lan says:

    Good day Mr. Seetharaman. Can you mail me the solution for your computations in the LED Lamp Circuit and Battery Charger Circuit? We made this really nice circuit as our project, and we need to justify every values measured in it. I have done some computations but I came up with different values with the one you did.

    I send my warmest gratitude and appreciation in advance for your candid response.

  • ram says:

    hi sir!i am a second year engineering student.i am gonna do a mini project on the automatic low power emergency light.sir,please tell me the operation of the circuit of automatic low power modified emergency light.i am not getting a clear picture of the working.

  • SUVAM says:

    Hii SIR, I want to know that in this circuit the led’s will on automatically in the power cut off ? Please please reply sharp.

  • Dii says:

    Hi Sir! Good day! I have a problem on connecting another bd140.. All leds including the indicator turns on while the power supply is on.

  • drix says:

    hi sir. am i gonna change any material if i use 5k potentiometer and 230v to 0-9 v 750 ma transformer? thanks. :))

  • Basit says:

    and also a 6.8 volt zener diode can be used or not.

  • Basit says:

    Sir I want to ask that can I use 9V 250mA transformer because I have one of it and the casing in which I am making this light has also do not have much enough space to adjust a 500mA transformer so what should I do to make the circuit compatible with 250mA transformer.

  • eshwar says:

    Nice project! what changes needed to be done to this modified version of the emergency light, to control the brightness of the LEDs, to conserve battery power and prolong the duration of the backup.

  • Dii says:

    Thanks for the reply! :)

  • Seetharaman says:

    Hi it should be atleast 2 watts.

  • Dii says:

    Hi Sir, how many watts is that 4.7 ohm resistor?

  • seetharaman says:

    Hi Naveed the PCB shown in the following project is for fully modified Automatic emergency light you can use the PCBs the layout and components are shown,
    http://www.circuitstoday.com/automatic-led-emergency-light#simple

  • naveed says:

    pcb required of this led emergency automatic schematic updated

  • naveed says:

    can you send me the pcb of led emergency light schemati

    waiting

  • seetharaman says:

    Hi Gurdeep The LED will glow when ever the battery is getting charged. once battery if fully charged it will go off.

  • GURDEEP SINGH says:

    when will the led nearer to transistor BC548 will glow.

  • Seetharaman says:

    Hi Gurdeep thanks for your feedback. this will give a positive approach and confidence for the project builders.

  • GURDEEP says:

    It is working perfectly.

  • Seetharaman says:

    Hi Nitin it is for setting the output voltage to 7.0volt by disconnecting the battery, hence the maximum output voltage is limited to safe value.

  • nitin says:

    one more question, what is working of varible resistance in this ckt?

  • nitin says:

    ok sir thank u.

  • Seetharaman says:

    Hi Nitin if you open circuit the zener only the stray and PCB leakages will affect but if it is in circuit it should operate normally. Have you checked R15 value it should be reduced to 330 ohms as I have explained earlier for LEDs to go off when mains is available. Kindly check your assembly step by step, there may be some mistakes, the above circuit is a proven circuit.

  • sasi says:

    sir,
    i need white led based brightest
    emergency light use with 12v
    7Ah battery and need back up
    for minimum 8 hours.which one
    is better constant current driver
    or pulse boost led driver. please
    suggest me some circuits.

  • nitin says:

    actually i had completed this ckt, but these problems(which i had stated as comments) are happening, please sir give solutions if any.
    Thanking you.

  • nitin says:

    so, if this is happening then under voltage protection ckt will not work, because during under voltage zener will not pass any current (open), but due to stray fields(as u said) leds will remain on, so is there any permanent solution?

  • Seetharaman says:

    Hi Nitin since T2 is a PNP transistor its base bias will from negative that is supplied by T3. (you may call it as return path of bias- T2 emitter base current flows through R17 T3 to negative.
    Check by shorting base emitter leads of T3 (by a screwdriver tip)light should go off, indicating no bias is available for T2. By opening Zener ZD2 the base of T3 is floating stray field / print leakage can pass some current to T3 which in turn can bias T2 for glowing LEDs.

  • nitin says:

    when i remove zener(open ckt), used in under protection ckt, then also leds remains on through battery, why?

  • nitin says:

    when i remove zener used in under protection ckt, then also leds remains on through battery, why?

  • nitin says:

    in ckt when transistor T3 is ON, then according to me current through R17 will be flowing away from base of T2 towards the negative terminal of battery through collector of T3, so potential across R17 will be such that it will be positive (bcoz of flow of current from right to left through R17) at base of T2 , so how will T2 (PNP) get turned ON?
    pls reply

  • sasi says:

    sir,

    i need white led based brightest emergency light use with 12v 7Ah battery and need back up for minimum 8 hours.which one is better constant current driver or pulse boost led driver. please suggest me some circuits.

  • seetharaman says:

    Hi Dap This is due to the gain of transistor BD140 you may reduce the value of R15 to 330 ohms to solve the problem, this I have explained in my earlier comment also.

  • Dap says:

    Sir, I have tried the modified circuit, my problem is the LEDs turn on while it is connected to mains. What do you think is wrong with the circuit Sir? When I tried to disconnect the bc548, r18 and zd2, it worked.

  • Ding says:

    Good day Sir! Can you please explain the current flow from input to output in detail? From the transformer to led. Hope you’ll reply. Thanks in advance :)

  • seetharaman says:

    Hi Ajitkumar remove T1 and check whether it is raising. if ok then the zener diode is defective. if no check the pot value and R1 value
    Hi chandru disconnect the power plug and use the on off switch provided to operate the light as a normal light

  • Chandru says:

    Sir,i saw your automatic low power emergency light circuit.It is automatically ON and OFF.But i want to ON and OFF it manually. What can i do?

  • AJEET KUMAR says:

    Hello Sir,
    LM317 Output volt (without connect battery)did not increasing maximum 6.6v. i will adjust vr1 4.7k, but volt adjusted maximum is 6.6v only. pls tell me solution of this problem.

  • seetharaman says:

    The PCB design is available with all modification in the following automatic emergency light simple model project
    http://www.circuitstoday.com/automatic-led-emergency-light#simple

  • AJEET KUMAR says:

    Hi! Sir,
    please send me the PCB layout art work for Automatic LED Emergency Light-Modified Version with low battery automatic cut-off system.
    Regards.
    ajeet kumar

    ajeet16@rediffmail.com

  • Seetharaman says:

    Hi Dojo for a 12 volt battery you require 13.8 volt cycle use, 14.4 volt for storage use and 15.2 volt for boost charging (to activate the battery). For 14.4 volts you can use one 12 volt zener with 3nos 4148 or 1N4007 is series with it to achieve the required protection. with battery disconnected set out put voltage at the wire connecting to battery with VR1 to 13.8 volts. (To achieve this your transformer should be rated for 12volts or higher)

  • DOJO says:

    Hello sir, thanks for the reply. As I wrote above, I’ve changed the circuit for 12V battery. In this case I think I have to set the pot VR1 for output of 13.5 Volts.
    I need the protection part, to keep the battery safe.
    These days I was thinking to do another experiment. to use a smaller voltage zener diode connected in series with a bipolar diode, like 11.5 volts (made of two zeners connected in series). Do you think that this may help on the higher tolerance zener diodes?
    Thank you in advance!

  • seetharaman says:

    Hi Dojo disconnect BC148 and set the pot VR1 till you get 7 volts at the battery end without battery connected. now connect the BC148 if the voltage falls down zener is of higher tolerance, if you feel you cannot get a better close tolerance zener delete bc148 portion fully, as this is only an additional protection towards over voltage. if you feel all these adjustments are difficult kindly use our simple emergency lamp circuit
    http://www.circuitstoday.com/automatic-led-emergency-light#simple

  • DOJO says:

    anyone? any idea why this circuit doesn’t work? It’s like the transistor bc548 acts like a resistor connected in parralel with the VR1. How can be fixed?
    Thanks

  • DoJo says:

    Dear Sir, I have the same problem as Rizky has. I’ve adapted this circuit for 12V/7Ah battery and used a 12V Zener for ZD1 and a 5K potentiometer. The problem is that the output voltage to battery is maximum 12.2 Volts, and it is variable only from 1.1 to 12.2 Volts. If I disconnect the zener diode, the battery voltage increases and can be set to around 13.5V (and up to more than 20Volts. I am using a 24Volt/4Amp transformer). What do I do wrong?
    Thank you!

  • Assem Shawkat says:

    Thanks Seetharaman.

  • seetharaman says:

    Hi Assem it is available in the net in various sites. this site is with all explanations and improvements for the help of hobbyists.

  • Assem Shawkat says:

    Who designed this circuit ?.

  • seetharaman says:

    Hi Chetan connect all bases and emitters together keep collectors seperately, connect to individual load line (LED groups of ten or twelve).

  • M.P Chetan says:

    Sir, how to connect BD 140 transistor, in series or in parallel.

  • Rizky says:

    Thank you Sir for your reply.
    I’ve been using 9-volt transformer. but indeed in my town is very difficult to obtain components with a precise value. not only the transformer, but all the available components have a large tolerance value.
    maybe I need trial and error until this circuit can work.

    Thanks a lot Sir.

  • seetharaman says:

    Hi Rizky i hope you are using a 9 volt transformer with the rated current capacity, if so no problem should be there. i think you are using a 6volt transformer instead of 9. The input voltage to LM317 will be 12.6 volt the drop across LM317 is 3volt hence you should get 9.6volt. temporarily disconnect ZD1 and battery measure the voltage output to battery with the pot you must be in a position to adjust 7 volt. now just connect the zener diode D1 and check the output voltage (still battery disconnected) if the voltage falls down your 6.2 volt zener is higher tolerance type actual voltage across it may be less than 6 volt. you

  • Rizky says:

    anyone can help me how to adjust the voltage?

    6.9-7volt at pin out lm317 or in terminal to connect to battery?
    during adjustment, the 6.9-7 volt achieved with a zener diode connected or disconnected (temporary) from circuit?

    thank you…

  • seetharaman says:

    Hi Chetan you have to use 4 nos BD140, you can use upto 48 LEDs. for 40 you drive 10LEDs with each BD140

  • M.P Chetan says:

    Sir, what changes I have to make for 40 leds.

  • Rizky says:

    Dear Sir,

    in other post you suggest to temporary disconnect zener and measure the voltage. i follow your suggest then i measured the voltage. at pin out lm317 raise to 8.41 volt, at cathode D5 7.82 volt, at end terminal (open circuit) 7.79 – 7.80 volt.

    then i check the zener diode and it is indeed true 6.2 volt zener diode. the installation was correct, the anode is connected to the output leg of R2 (1.2k) and the cathode is connected to the output leg of R16 (4.7/5w).

    thank you Sir.

  • Rizky says:

    Dear Sir,

    i am new in electro. i confused how to adjust voltage. where i must check 6,9 volt – 7 volt? at pin out lm317 or at end of terminal (to battery)?

    if you mean 6,9 – 7 volt at end terminal (open circuit without battery), would not that would open the zener diode and send bias to t1 then causes the voltage breakdown (t1 thought that the battery is full)?

    thank you Sir.

  • Rizky says:

    Dear Sir,

    I assembled your circuit, but i have problem. with 10k pot in highest resistance, the voltage after R16 (4.7 ohm/5watt) only 6.21 – 6.26 volt.
    and then i checked other point, output from rectifier diode (D1-D4) 9.5 volts, voltage after c1 and at pin in lm317 9.5volt. voltage at pin out lm317 drop into 6.8 volt, voltage after D5 (Chatode) drop into 6.3 volt, ad then voltage after R16 drop into 6.21 – 6.26 volt.
    what wrong with my circuit? thank you for Your help Sir.

    Rizky

  • Rizky says:

    Dear Sir,

    i assembled the circuit, but the voltage output for connect to Battery only 6.26 volt.

    i use 10k pot vr. the voltage out from D1-D4 9.5 volt, after C1 still 9.5 volt. at lm317 pin out the voltage 6.8 volt. and then after D5 voltage drop to 6.3 volt. after R16 (4.7 ohm/5watt) voltage drop to 6.26.

    i try to charge the battery but the voltage of battery only up to 6.41 volt and not raise again.

    what wrong with my circuit Sir? thank you for your help Sir.

  • seetharaman says:

    for36 LEDs of 3volt 25mA you require 3nos BD140 LED drivers with each stage driving 12 LEDS. you require 900mA current say 1amp for 12 hrs use you require a 6 volt 12AH battery. the charger should be capable of 3amps same above circuit with ICLM338 instead of LM317.

  • Yogesh says:

    Dear Sir,I want to use 36 LED’s working for 12 hours, then what capacity of battery i needed? What kind of changes required in circuit?

  • Pete says:

    sir, in the first time i run my project it was running normal but yesterday my project got into trouble. how can i fix it? this time even if the lamp is in a source, it still light. what should i do to fix it sir?

  • seetharaman says:

    Hi Rana why do you want to waste energy, anyway you have to use 5 ohms 2watt or 5 watt.
    Hi Pradeep refer to my other simple emergency light project.
    Hi Vaibhav SCR cannot be used.

  • vaibhav says:

    can 1 SCR handle the operation of both t1 & t3

  • pradeep says:

    sir,i assembled the circuit and it works very fine. during the day time also if the supply is off, light is switched on. in order to stop this i suggest to connect an ldr. but where to connect it?and another thing is that what is the maximum number of leds can be used in the circuit?

  • rana sarwar says:

    my dear sir i have 6 volt acid battery and 24 LED in parallel circuit how much resistance value i use in circuit thanks

  • Seetharaman says:

    Hi Richards you are correct it is EBC. If you are using 4.5AH battery and say your load is 50mA each chain 12chains 600mA. Hence the battery should last for 4500mAH / 600mA roughly 7hrs. To Find out the current use 2nos LEDs inseries apply 6volts DC to it check the current drawn.
    http://www.datasheetcatalog.org/datasheet/MicroElectronics/mXvusvr.pdf
    Hi Shruti I dont understand your requirement.

  • SHRUTI says:

    sir, can we modify the above circuit by using atleast 4 transistors.. i need to know it within 2 days .. please help me out…and please mail me the circuit

  • richard says:

    hey pete maybe you could help me with my questions :(

  • Pete says:

    Thank you sir for the help. My project was successful, although i made some few changes it still works. I will share to you my few changes later. Now i have to work for the documentation of my project.
    Thanks a lot for you’re help.

  • richard says:

    i need to show in my paper how to calculate the time that the battery can supply the power for continuous illumination.. i used the 6V 4.5Ah batt. what’s the formula ? thanks

  • richard says:

    im using 8550 transistor instead of BD140.. the pins are E B C right?

  • richard says:

    Seetharaman please answer me :(

  • richard says:

    how do i know if the leds im using is rated for 25mA or 50mA??

    the indicator still glows even if the battery is not connected. what to do?

    how do i use the multimeter to check the charging voltage of potentiometer?

    how long does it take to recharge 6v battery?

    what’s the max. area achieved by the light?

    how long can the battery supply the power for the emergency light?? if you could provide some calculations, please give me .

    thank you.

  • richard says:

    no more fireworks for today :) im so glad. i connected the wiper to the indicator. the circuit’s already ok. when connected to mains, the battery is charging. when unplugged, the LEDs glow..however, i still have the problems about the LEDs. :( guess i’ll be workin on it when im not busy again . thanks man

  • richard says:

    where do i connect the wiper of potentiometer? im redoing the whole circuit again. i realized my mistakes lol

  • seetharaman says:

    Hi Richard The circuit is correct. Each loop is rated for 6 volt as the LEDs are rated for 3.0 volt at 25mA the excess 3.0 volt is dropped, by 0.6volt at BD140 and balance 2.4 volt is dropped across 100ohms series resistance.

  • richard says:

    the leds are connected in parallel, and the resistors are in series. is this correct?? thanks.

  • seetharaman says:

    Hi the pcb shown is for the fully modified mode including low and high cut off. it is not exactly for the simple version, for simple version also it can be used by introducing suitable links.

  • josh says:

    dear sir,
    thank u for earlier reply.. sir , is it possible to assemble modified version of your circuit on simple emergency PCB ? if you have PCB layout for the Modified versions of the circuit ..plz provide to me.. realy i need it.. plz make areply.. waiting for your reply.. joshnair@yahoo.com

  • seetharaman says:

    Hi Pete it is for limiting maximum charging current. you can use 5 ohms 7 watts. you can use two 10 ohms 3watt in parallel.

  • Pete says:

    sir,i can’t find exact 4.7 ohms for the r16. r16 is for what sir?

  • seetharaman says:

    Hi Josh the PCB is available for the fully modified version in Simple version of this LED PCB and Supply PCB
    http://www.circuitstoday.com/automatic-led-emergency-light#simple
    Hi Aseem ZD1, T1 and R2 required to cut off charging of battery once its terminal voltage reaches 6,9 to 7volts.

  • Assem Shawkat says:

    Dear Mr. Seetharaman
    I need some more detailed information about the function and operation of ZD1, T1 and R2. I appreciate if you send me any documentation you might have to my Email address:
    assemshawkat@hotmail.com
    Thanks/Regards

  • josh says:

    dear sir,

    i have assembled the ciruit in a general purpose pcb.. its working ..nice..realy ur circuit is usefull..sir, will you plz mail the pcb and its layouts if you have designed it.. i really need it.. hope that u will help me.

    thanking you in advance for your kind consideration

    joshnair@yahoo.com

  • seetharaman says:

    Hi Richard to isolate the problem without connecting to mains, link collector and emitter of BD140 if the LEDs are glowing normally, indicates problem around BD140. If the glow is still bad check the battery voltage and the resistance. may be you have to check the LEDs individually. Try the first step you will succeed the collector base emitter pin outs are different for BD140 from the traditional pin outs. watch.

  • richard says:

    ohhh it’s already workin but the LEDs dont emit uniform lights, and only 6 LEDs are workin..

  • richard says:

    are the LEDs connected in parallel and the resistors in series? or i have to connect it the other way?

  • seetharaman says:

    Hi Richard if you donot want it say during day time when you are away you may not need it hence the switch is shown,
    Hi Pete you can use 8550 most recent transistor for BD140 for BC148 you can use 2N2221 or 2N2222.

  • Pete says:

    Mr. Seetharaman,i can’t find BD140 and BC548 what can i substitute for this components?

  • Pete says:

    Mr. Seetharaman,i can’t find BD140 and BC548 what is the substitute for this components?

  • richard says:

    do i have to put the on&off switch?? it’s supposed to be automatic right?

  • Assem Shawkat says:

    Thank you Mr.Seetharaman

  • Seetharaman says:

    Hi Aseem you require 2.5 mp power pack. ou have to change the transformer to 9volt 3amp capacity. change all 1N4007 rectifiers to 1N5404. change LM317 to LM338 with proper heat sink. other components need not be changed.

  • Assem Shawkat says:

    Hello Mr. Seetharaman
    If I will use a 6V 10Ah battery, what components need to be changed in the circuit?.
    Thanks/Regards.
    Assem Shawkat.

  • vinod says:

    Juan, 230V 50Hz is the AC power supply you get from a socket on your switch boards in your house. please take a two pin plug, cut it at one end you have two wires now, connect these two wires to your transformer primary.

  • juan says:

    Seetharaman or anybody out there, i just wonder what do you call that part of “230V 50Hz” ?? i mean what shall i tell the seller if im gonna buy that part? i already have all the parts excet this one .thanks

  • juan says:

    @pete, 1/2 watt

  • Pete says:

    another thing sir, the resistors is it 1 watt or half?

  • Pete says:

    can’t find 6 volt 2-3 watts, only 220 volt 3 watts, is it ok?

  • Assem Shawkat says:

    Mr. Seetharaman
    If I will use a 6V 10Ah battery, what components need to be changed in the circuit?.
    Thanks/Regards.
    Assem Shawkat.

  • seetharaman says:

    HiJuan no need to change anyother component.
    Hi Pete the PCB is available in
    http://www.circuitstoday.com/automatic-led-emergency-light#simple
    LM317 has no replacement. if you can get LM7808 fixed 8 volt regulator you can try the above simple proven circuit.

  • juan says:

    AM i gonna change the materials if i use 5k pot? i’m excited to do this one since we always experience loss of electricity here in philippines.

  • Pete says:

    sir, what is the other substitute for the LM317? i can’t find one here.

  • Pete says:

    Sir, can you also please send me the layout of the pcb?
    If you could, please email me here. caballarpet@yahoo.com
    tnx sir.

  • Pete says:

    Thanks a lot sir, it really helps.

  • seetharaman says:

    Yes Pete delete R3 to R14. use one number 6volt 2 to 3 watt bulb.

  • Pete says:

    i mean, or neglect the r3-r14?

  • Pete says:

    Sir, if i use 6volt 2 to 3 watts bulb in place of LEDs, do i still need to add r3-r14? on neglect it?

  • juan says:

    AM i gonna change the materials if i use 5k pot? i’m excited to do this one since we always experience loss of electricity here in philippines.

  • maegan says:

    thanks so much!!

  • seetharaman says:

    Hi Maegan that is charge indicator. once the charge is complete the LED will go off. With LED with 2.2K you cannot get open circuit voltage of 6.9 to 7.2 volts (without connecting the battery) hence you have to increase to 4.7K In place of BD140 you can use the recent 8550 PNP planar epitaxial transistor. You can use 5mm high bright white LEDs . Hope this will help.

  • maegan says:

    (a)in the modified version (not the voltage cut-off protection), the pot to be used is 4.7K or 2.2K??
    (b)and also what could be an alternative for BD140?? i can’t find one..
    (c)can i use 5mm white LEDs instead of 10mm??
    (d)what is the purpose of the LED near the IC and 1K resistor??

    please answer briefly.. i want to do this for our project..

    thank you! God bless you! im sorry if i have too many questions..

  • maegan says:

    (a)in the modified version (not the voltage cut-off protection), the pot to be used is 4.7K or 2.2K?? (b)and also what could be an alternative for BD140?? i can’t find one..
    (c)can i use 5mm white LEDs instead of 10mm?? (d)what is the purpose of the LED near the IC and 1K resistor??
    please answer briefly.. i want to do this for our project..

    thank you! God bless you! im sorry if i have too many questions.

  • seetharaman says:

    Yes Pete you can use 6volt 2 to 3 watts bulb in place of LEDs, BD140 can handle load up to this value. The PCB drawing is available for the modified version itself.
    http://www.circuitstoday.com/automatic-led-emergency-light#simple
    Hi Maegan it is for rectifying AC voltage to DC voltade.

  • Pete says:

    sir, can i use a light bulb instead of LED?

  • Pete says:

    sir, i can’t picture the view of the circuit board, can you please attach some pictures of it? thank you sir.

  • maegan says:

    Hi may i know what’s the purpose of D1-D4??

  • seetharaman says:

    Hi Rej it can be done on breadboard.

  • rej says:

    please answer seetharaman

  • rej says:

    can this be done in breadboard? i’m really a newbie in doing circuits.

  • seetharaman says:

    You have to change the transformer with 15 volts 2 amps rating. replace LM317 with 337. replace the voltage set pot to 10k so that the output voltage can raise to 15.2 volts DC on ouput open circuit,

  • murali says:

    sir i want to replace 6v 4.5ah battery to 12v 7ah please tell me what or d changes required

  • Pete says:

    Sir,
    It helps a lot. Thank you sir.