An Automatic LED Emergency Light circuit is designed to turn ON when there is no adequate lighting or if the power supply is cut-off. Earlier fluorescent lights were used to build such circuits. But the use of LEDs has proven to provide adequate lighting for a longer period before draining the battery.

We have developed three circuits under Automatic LED Emergency Light. Two of them are designed by Mr. Seetharaman, a very valuable and important contributor to this website. We have listed the circuits here for your ease of reading. If you have any doubts; please comment on the circuit name or circuit number.

1. Simple Emergency Light Circuit

This is one of the most cost-effective (cheap) and simple emergency light circuit developed for CircuitsToday – This is an automatic emergency lamp with daylight sensing, means it senses darkness/night and turns ON automatically. Similarly, it senses daylight and turns OFF automatically.

We have designed a simple emergency lamp circuit that does not require any special equipment; even a multimeter to assemble and use. Any individual who can do a good quality soldering must be able to build this circuit successfully. This can be easily accommodated in the defunct two 6 watt tube National Emergency Lamp or any PL tube type emergency lamp. The difference will be in the working; it will work non stop for more than 8 hours. Deep discharge is taken care of by the LED characteristic and overcharge protection is taken care of by the fixed voltage regulator. This uses a simple 3-Pin fixed regulator that has a built-in current limiting circuit. The only required adjustment is preset which has to be set to ensure the LEDs just light up (it should be left at that position). The 5mm LDR is just mounted on top of the emergency light as shown in the photograph. LDR is used to avoid it lighting up during day time or when the room lights are ON. 2 LEDs are used in series; the dropping resistance is avoided and 2 LEDs light up with current that is required for a single LED,  by which energy is saved to a great extent.

Note: This circuit is developed by Mr.Seetharaman for readers of CircuitsToday. This particular circuit has been kept so simple for people who have limited access to components or in other words, this is an emergency light circuit that you can build with minimum components. In addition to the circuit diagram, He has shared photographs of the prototype he made in National emergency light and a PCB design.

Simple Emergency Light Circuit Diagram:

simple emergency light

Photographs of prototype made in National Emergency Light:

Emergency Light Circuit PCB Design:

PCB Design and Diagram of Automatic Emergency Lamp
PCB Design

2. Automatic LED Emergency Light

NOTE: Considering the doubts raised by many of our valuable readers in our Comments section, this circuit has been modified by Mr.Seetharaman, one of our valuable contributors. You can see his modified circuit here: Automatic LED Emergency Light Modified.


This is the circuit diagram of a low-cost emergency light based on a white LED. The white LED provides very bright light which turns on when the mains supply is not there. The circuit has an automatic charger that stops charging when the battery is fully charged.

The IC LM 317 produces a regulated 7 V for the charging of Battery. Transistor BD 140 drives the output. Transistor BC 548 and Zener diode controls the charging of the battery.


It is always better to connect a heat sink with BD 140. Before using the circuit output of LM317 must be set to 7V by adjusting the potentiometer.

Automatic LED Emergency Circuit Diagram:

Automatic led emergency lightNote: R3 to R14 are all 100 ohms

3. LED Emergency Light – Modified Version

The most modified and best version for this circuit is intricately explained with a neat circuit diagram and a 2 part explanation. One part is the LED lamp light circuit and the other is the battery charger circuit. All current ratings and voltage ratings are perfectly calculated with basic and clear instructions.  A further modified version is also available where under-voltage cut-off protection is provided for the LED emergency light circuit. You can find the circuit here.

We have more interesting Lighting circuits for you, please take a look:

1. LED Ramping CircuitAn interesting LED application with help of a ramping circuit.

2. Flashing LED UnitA circuit application to flash many LED’s.

3. Puff to OFF LED circuitA simple, hobby and more of a fun circuit where you can turn OFF an LED with a puff.

4. Street Light CircuitWant to build a street light application? This is the one you are looking for.

5. Light Activated SwitchA circuit application to make a switch activated when light falls upon (and vice versa).

When I was in my young days, I always had this desire to build an emergency light application. I’ve successfully built one during my high school days. I hope you enjoyed building these circuits and understood the concepts behind each. I wish you all learn more about electronics from our website. Happy learning days.


a simple emergency lamp no need for any special equipment even a multimeter to assemble and use this. Any individual who can do a good quality soldering can build this successfully. This can be easily accommodated in the defunct two 6 watt tube National Emergency Lamp or any PL tube type emergency lamp. The difference will be it will work non stop for more than 8 hours. Deep discharge is taken care by the LED characteristic and over charge protection is taken care by the fixed voltage regulator.

This uses a simple 3Pin fixed regulator which has a built in current limiting circuit. The only required adjustment is the preset which has to be set to ensure the LEDs just light up (it should be left at that position). The 5mm LDR is just mounted on top of the emergency light as shown in the photograph. LDR is used to avoid it lighting up during day time or when the room lights are on. 2 LEDs are used in series the dropping resistance is avoided and 2 LEDs light up with current by by a single LED,  by which energy is saved to a great extent.
Hope this project will be acceptable to most of our readers, who has minimum instruments.
I am attaching the photos of my prototype in an National emergency light and also the PCB design.


  1. sir we reqired 10w 12w 15w 18w 22wled drives ple conncts me


  2. sir i want to use 18 leds in your ckt plz what are the changes required plz its immediate

  3. Madhusudhan

    Hello can u please provide Emergecy charging light change the battery what type of battery best tell me

  4. Dar mushtaq

    What will happen if BD140 and BC548 are removed from circuit

    • Seetharaman

      to isolate electronics from battery when power supply goes off. if you remove both the transistors the emergency light will not work when power goes off.

  5. charles Ehinne

    How can I design and construct a 100 LED rechargeable lamp wit 6-volt battery an three switch off low and higher, c

  6. Soumitra Danda

    What changes are needed to be made to “Simple Emergency Light Circuit” to make it operate manually and how long is it needed to be charged to make it
    fully operational.

  7. sir how do you connected the the 10k resistor to another 10k resistor from the IRF? i didnt understand it please tell me

  8. 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?

    • Seetharaman

      No rohit the charger voltage on no load should be around 6.9 to 7.2 volts. try by replacing the faulty component.

  9. Sir, what modifications can be done in the LED emergency light project so that it senses the intensity of the light and glows when the intensity is low and doesn’t wait for complete darkness. I was thinking if this can be used in our vehicle headlights. In that case we will have to take care that it senses only the solar radiation or else the light coming from the other vehicles and streetlights will affect the functioning of our project. Please do guide me in this.

  10. sir can you plz tell me the working of first circuit in which LDR and Voltage regulator nd mosfet are used.
    can you plz give me brief description of working ?

  11. Pravesh Pradhan

    Sir, can you please explain the working of:
    (i) IC LM 317
    (ii) Transistor BD 140 and
    (iii)Transistor BC 548 in the above circuit.

    And how does the charging stop automatically once the battery is fully charged?

    • Seetharaman

      i) LM317 is a voltage regulator it will maintain the rated 6.9 to 7 volt for charging the battery.
      ii)Transistor BD140 is to switch the LEDs automatically from battery when power fails.
      iii) BC148 to cut off charge once IC voltage goes beyond 7.4 volts as protection, when VR1 is disturbed inadvertently.
      once the terminal voltage of the battery is nearing the set 6.9 volts the current drawn for charging the battery will be just equivalent to self discharge current of the battery, so only topping up action no over charge will take place. Setting VR1 for an open circuit load should be set within 6.9 to 7.2 volts to take care of the above action.

    • Zeeshan umer

      ANS 3) as the zener’s is of 6.8v so when the battery’s potential equalizes it then
      automatically it stops charging as potential on both sides will be same( as u already knows that conventional current always flows from higher potential to lower potential).
      Ans 2) antually it is the PNP transistor as when the 220V supply is on the base current is higher but as we cut of the supply the battery which is connected to its emitter current starts flowing through it due to which the collector current remains equal to IE therefore LED’s starts glowing.

  12. what type project is more useful in these days…?

  13. hello !! can you please provide me the ckt diagram of collision avoidance bot?? as soon as possible , please !

  14. hi… i wanna know that in first circuit we have to use 4 leds or a set of leds?? reply as soon as possible plzz… n yeah can we use 9V battery instead of transfomer???? n last in 1A bridge is it inbuilt or we have to use 4 diodes??

    • Seetharaman

      Hi minimum is 2 LEDs and you can use multiples of 2. for a 6volt 4.5AH battery for an 8 hrs non stop illumination you can use 10 sets, that is 20 LEDs
      You can use a 9volt 10amp battery.
      1amp bridge rectifiers are available in the size of 4pin DIP package quite economical or you can use 4nos conventional 1N4007.

  15. saqib ahmad

    i am new to this site if line of c1 capacitor break out how i will place it?

  16. V.Pugazhenthiran

    Sir, How can we modify this circuit to use 12v 7.5ah battery with 24 Led’s. Awaiting for your reply.

  17. Hi,
    Can i have 100 LEDs and if so what are the modifications.


  18. chinthaka

    I am a new one for this website i am in serching for charge 6v 4.5Ah battery and light up a bulb to use in night so i havent found full circuit to do that pls design a circuit to do that and also protect it by deepdischarging and by overload charging if you can use transformer in between 0 – 9 v , gladly i want to say your contribution towards this feild and helping to beginiers who are not very well known about circuits . Thank you

  19. nice project,but In the case I use 12V battery what will be the values of the zener,the transformer output….etc Thanks

  20. Hello Mr. Seetharaman, I must say without mincin words that you are a great blessing to the generation of upcoming engineers and hobbyist. I am new on this website but I will go try one of your projects right away and I will give you feedback on it. Once again, thank you for your impactful knowldge. Have a nice time.

  21. hello friends.had any one done the first emergency led lamp with ldr.i think the pcb detail of that project is not matching with schematics.plz some body help here

  22. Hi Sarkar you can use my earlier project with 50LEDs of 25mA bright white variety (instead of 3volt 50mA high bright 4 pin variety)replace 1uF capacitor with 0.68uF 400volt polyester variety no other changes are required. hope you want it for 220volts 50Hz operation.

  23. Dear SitaRaman,

    The Chinese made emergency lamp failed; I opened it. It uses a 2+2=4v bty; one Transistor, 1 indicator red Led;
    2 capacitors; 4 resistors and 6 diodes. It works in AC 220v. There is a switch by which we can manually operate it. It can auto switch when mains fail. It has no transformer, IC etc. It auto charges. It has 20 white LEDs.

    Can that cct. be explained??

    • Seetharaman

      Hi Mahesh for Ni Cad batteries we can use capacitor with limiting resistance which will become a constant current source to charge. But for Lead Acid Gell cells voltage regulation with maximum charging current is important. The LA battery will fail if you leave it on under charge continuously. The operation is similer to following circuit. With diode D2 in base circuit with supply on the transistor will be reverse biased once supply fails it will conduct with forward bias through resistance R2. Connect a switch in parallel with the transistor.

  24. Seetharaman

    Hi Manjunath with fully charged battery it will work non stop for 6hrs.

      • Manjunath

        Hi sir….
        I am doing first circuit… in that circuit, across transistors its 10k is variable or normal resistors sir…

  25. Can’t we make the Emergency Light which use to depend on the both solar power as well as Electricity ……………. If so possible please give me the detailed information in relation with the same with it’s list of components & it’s easy circuit diagram…………

  26. Santu Sarkar

    Respected sir,
    I want to know what is the color code & watt R1 to R15? Please mention it.

  27. Sadiq tobi

    Hi Mr Seetharaman Plz sir i need d lists of components in d construction of an emergency lamplight using remote control i also need the circuit diagram of dis device.plz send it to my mail

    • Manjunath

      Hi Sir,
      I am interested to do this circuit can u tell the how much hour the LED glows after power failure… for 25 LED’s.

  28. Santu Sarkar

    Respected sir,
    I want apply only 220v on 50 Leds set (3v 50mA high bright leds ).This is not Emergency. So I asked you that I have required any diode or resistor?

  29. seetharaman

    Hi Sarkar you can use my earlier project with 50LEDs of 25mA bright white variety (instead of 3volt 50mA high bright 4 pin variety)replace 1uF capacitor with 0.68uF 400volt polyester variety no other changes are required. hope you want it for 220volts 50Hz operation.

  30. Santu Sarkar

    Respected sir,
    How to make a 50 leds set. That is on by 220v. I have required any diode or resistor? Plz explain me.

  31. seetharaman

    Hi Sarkar automatic means the light should come on once the supply fails (this happens in the second circuit even during day light). Still for automation, it should not glow in the daylight or any other light source available in the near visinity. This point is taken care in the simple emergency lamp (first circuit). hence it is fully automatic. that is once power fails, if it is dark without any other light source in the near visinity this light will switch on automatically.

  32. Santu Sarkar

    Respected sir,

    I was going through with the circuit diagram and wanted to work on it, sir i want to know what exactly Automatic means in this project i mean what is the process of its charging and how does it work. i really wants the complete informations related to this circuit in detail sir i’ll be highly thanks full to you if you reply me for all of my queries and asks i want your support for it because this projects is very much knowledge able for me please reply me on my mail address
    Thank you

  33. Santu Sarkar

    I want to know what is the color code & watt R1 to R15? Please mention it.

  34. i do not electric & electronic knowledge but when i saw this article i’m interested to do so. can you help me to arrange an Automatic LED Emergency Circuit for me, i can pay you. how much it costs? will u do for me?

  35. Really like the Auto Emergency Light,,,Nice Design;;I Like!!!

  36. pis sir i need full description about the above circuit diagram

  37. samuel m koroma

    please sir,i want to see the full write up of the simple emergency light circuit

  38. sir please tell ur mail id. i want to discuss something about my project.

  39. sir i need the charger circuit for 14.4 v 4.5 AH laptop batery.
    it was made by using 3.7v,2200 mAh samsung li-ion battaries.
    it was made using 8 bataries 4 in series and parallel connection.
    how to charge the battary? i want this to use it for the emergency lamp.

  40. Seetharaman

    Hi Prasad you can use 24LEDs for a bright and long time lighting. use one more BD140 in parallel (base and emitter in parallel)and to its collector connect another group of 12 LEDs. The brightness will be equivallent to 11watts energy saver light and it will give you 7hrs non stop with fully charged battery.

  41. Hi sir,

    Maximum of how many LEDS can be connected in this circuit to get high brightness and good battery back up. Plz suggest

  42. Seetharaman

    Hi prasad it is required for the light to come on automatically. Day time the light will be off and night it will turn on automatically. If you donot want the facility you can do away with R15 and T2 just use only the on off switch with LEDs. This will bec ome a solar light (charging the battery with solar energy and use it as lantern during night whenever required)

  43. Hi sir you replied for my question like below—
    Hi just buy a solar panel capable of 500mA at 12 volts. connect it through a scottky diode(2N5819 or similar)to LM317 input by deleting X1, D1 to D4.

    My Main concern is “Should i retain R15 resistor and T2 BD140 transistor in the circuit or not” for Solar powered emergency lite.

  44. Seetharaman

    Hi Prasad sorry not addressing your name. it suits both the questions you can use solar cell of the capacity indicated.

  45. Was this replied for my question or not. I have doubt so clarify me plz. If its replied for me then should i retain R15 resistor and T2 BD140 transistor in the circuit or not.

    Hi Kumar just buy a solar panel capable of 500mA at 12 volts. connect it through a scottky diode(2N5819 or similar)to LM317 input by deleting X1, D1 to D4.

  46. Seetharaman

    Hi Kumar just buy a solar panel capable of 500mA at 12 volts. connect it through a scottky diode(2N5819 or similar)to LM317 input by deleting X1, D1 to D4.

  47. Hi
    I need to do Automatic LED Emergency Light using Solar power.
    Please suggest necessary changes and modified circuit for Solar Emergency LED lamp with good brightness. Email:

  48. Hello sir, can u help me to do the same charger without a transformer and also protection of battery against over charging in it?

  49. David Colin

    Hello sir

    I have a requirement for the above emergency light circuit but with the following alterations;

    1. we need to use an off the shelf 12V 1W lamp and so need to increase the battery size
    2. we would like to see a “charging” indicator LED to confirm the mains are on.

    Can you advise what changes would need to be made please

  50. seetharaman

    Hi Shrikant no need for any calculation you can just go ahead constructing. Hi Rubel LM317 is a constant voltage regulator to protect the battery against over charge once the terminal voltage reaches the rated voltage it will bring down the voltage through zener ZD1 and T1. This is an additional protection against over voltage.

  51. Rubel Dhiman

    hi sir………….
    please explain the working of circuit no.2…….i am little confused with working of transistors and lm317.. please explain sir….

    rubel dhiman.

  52. 1) there is need of calculation for power supply. or directly we connect it given in the ckt diagram

  53. Seetharaman

    Hi Ali In the first circuit 7808 is the regulator for the charger circuit. Mosfet is used for switching the LEDs, with very low drop in voltage. LDR is used for switching off the LEDs during day time/ when ambient light is available from other sources.
    In the second circuit 317 is the regulator for charging circuit and BD140 transistor is the LED driver.
    Hi Edgardo thanks and I am back to India.

  54. Muhammad Ali

    I do not understand 1 emergecy light circuit.Please explain me

  55. i need an assist toward my project in the constrution of a low cost-automatic emergency light, av been searching for a v.resistor 2.2k and 16k 5watt resistor and i cn’t get it pls can their be a sustitute for the above mentioned or wherelse can i get it

  56. Sorry,
    HAPPY NEW YEAR inadvance to you


  57. Hello Seetharaman,
    Good day and advance HAPPY NEW TO YOU..
    My inquiry is this;
    for the circuit Automatic LED Emergency Circuit Diagram, what value of ZD1 I will connect in the case of 9.6 volts Nicad rechargeable battery I will charge, and what value also for ZD1 if I will charge 12volts, 9Ah rechargeable batteries, just for flexibility on use of this circuit. I like this circuit, very simple.
    And maybe I could make use of this circuit for my interne router requiring 5VDC, 1A supply, of course I will connect a 5V regulator (LM7805) from battery B+ going to the router power supply input.
    Can this be ok?
    Best Regards

  58. Priyaranjan

    Dear Sir,

    I followed the modified circuit.But I have two problems after completing the circuit
    i)Red LED is not glowing even the battery voltage is 5.8 volt (In charging condition)
    ii)Battery is maximum charged up to 6volt.I modified the circuit with 4.7k POT.

    Please help.


  59. ankit sharma

    hi, i assembled the automatic LED emergency light but there occurs a problem , all LEDs are turn on when i plugged the mains supply.plz help sir

  60. Seetharaman

    Hi Nitin refer the modified drawing it has got the low voltage cut off also. regarding the simple version as there are 2 3volt LEDs in series they will not glow ar 5.3 volt hence no conduction no deep discharge. once the LEDs are not glowing plug emergency light to mains for charging. All these were taken care during the design.

  61. sir,
    I need a led based emergency light with 12v battery.minimum back up time 8 hours….please post some circuits it’s very useful…,

  62. this circuit is outdated, switching of this ckt depends on mains power, but when battery goes under voltage then also led remains on and damages battery performance by deep discharging.

  63. Seetharaman

    Hi Ramasami it is a LEAD Acid Gel cell of 4 volts. You connect to supply for 24hrs and keep it away. Use the light once the LED brightness comes down charge it over night and disconnect and keep it. if dont do that the battery will get over charged and the battery life will come down drastically, may be in 6 months you have to go for a new battery, which is not available in India at present. Available ones are just activated ones. In the above circuit all are taken care. Afteral for Rs140/- that is all you can expect from Chinese. These products cannot enter USA market. These get into India market due to our greedy traders.

  64. Ramasami. V.

    Dear SitaRaman,

    The Chinese made emergency lamp failed; I opened it. It uses a 2+2=4v bty; one Transistor, 1 indicator red Led;
    2 capacitors; 4 resistors and 6 diodes. It works in AC 220v. There is a switch by which we can manually operate it. It can auto switch when mains fail. It has no transformer, IC etc. It auto charges. It has 20 white LEDs.

    Can that cct. be explained??

  65. Seetharaman

    Hi Umer if you are using Simple emrgengy lamp circuit change 7808 regulator to 7806 regulator no other change is required.
    If you are using LM317 circuit adjust outpur voltage for 5volts at battery terminal end, without battery connected. reduce R16 to 12 ohms and reduce ZD1 to 4.2volts

  66. sir how to modify charger circuit to charge a 4V 0.7A lead-acid battery?

  67. seetharaman

    Hi Hari for 12volt 7AH attery you require an output of 14.0 volts at 2amps. you need a major design change.
    With 1/2 watts LEDs 8 LEDs (4 in series in each loop) will work for 20hrs non stop.
    You can use the charger appeared earlier in this column

  68. M Sikandar

    Dear Sir,
    for my university project. If you have any thesis or any material then Please mail me I realy need this.


  69. seetharaman

    Hi Jayaram ask for high Bright white LEDs. For LM317 see the datasheet on net. the total cost will be less than Rs500/- excluding box. if you have any old defunct one at home use its enclosure by removing all materials from inside. for lm317 see the following link.
    Hi Paras you can use for blinker standard amber 5mm LEDs 5nos in series with 20mA constant current source using simple 2 transistors. For head lamp use super bright white LEDs 4pin type (rated for 50mA @ 3 volt. use 3 LEDs in series with 50mA constant current source. if you get 3 volt LED driver ICs use them they SMPS can take wide range of in put voltage and drive high currents the most suited for your type of application.

  70. Hello Seetharaman,

    i got 12V 7 Ah Battery …… So please explain the circuit changes…
    how many leds(1/2W) are used for 7Ah battery…?

    plz help me…..

  71. i got 12V 7A battery so can any one pls modify this circuit for it and i need more bulbs too pls help me

  72. i am not an electronics engineer.but i would like to try this one(automatic led lamp) out.i don’t have any idea of selecting led’s for the circuit.kindly mail me answers of the following queries:

    1. how do i rate the led’s.(i need to tell the shop owner the ratings, is’nt ) do i find the polarities of various components like lm317 etc

    3.appropriate cost of each components.



  73. Hello sir,

    I want to modify my kinetic honda’s blinkers & tail lamps..
    with LEDs…

    plz help me to design circuit….& also give me the details of material requires…..

    we offanly see this types of lights r now used in forein countries….

  74. This Is a Interesting and Practical Circuit that is useful to have around the House Even If You aren’t Crazy about Building Stuff!!

  75. HELLO SIR,
    I want 24volt/10amps smps circuit with battery(half an hour backup).If power fail go to battery mode. this my project .pls send me circuit as soon as possible.
    Thanks & Regards
    S.Syed Babu

  76. seetharaman

    Add one more 1N4007 diode in series with the existing 2 diodes. this may be due to the 7808 IC.

  77. sir, battery charging volt is to reduce 7volt.pls reply me.

  78. seetharaman

    Hi Bhoopesh good idea. connect only 2 LEDs in normal mode (low light mode) and connect all LEDs for high brightness. This can be carried out through a switch. When ever you go out put it on to – low light mode. once you return locating light will not be a problem as it is already lit, now switch to full bright mode.

  79. Hi Seetharaman,
    Yours is a wonderful circuit.But I like to have some modifications. Can you suggest?.
    In the circut, the emergency light goes on with full power when main power fails (LDR function will of course work) and remains till power returns.

    Modification I like –
    On main power failure, the Emergency light should switch on at full power, all LED’s. But after a while – say after 1 minuter or 2, almost all LED’s should switch off, expect 1 or 2 LED in low brightness. (of course let there be LDR function included).

    Benifit – usually the Emergency lights switch on always when power fails, and stay lit till power returns – even if no one at home/even if everyone is sleeping!.

    My suggestion will over come this.

    After the main LEDs got switched off after 1 or 2 minutes of power failure, we should be able to switch on the same (main, all LEDs) by some switch (pull to?)
    This happen only if there is inhabitant or through PIR sensors!.
    This full LED re-lighting has to be linked to auto switch off on power resuming.

    I know linking PIR sensor is bit complicated.
    But most of the LED switching off can be done through some timer ICs?.

    Can you give some suggestions?
    And about me, I am basically a medical doctor but with a strong hobby in electronics

  80. Seetharaman

    Hi Amit if you have 12volt 5Amp transformer, use two 5403 rectifiers and a 3.3 ohms 20watts resistance in series to limit the current to charge the battery.

  81. amit kumar dev

    hi its amit.i have a yb5l lead acid battery used in bikes of 12v,5Ah range.i have 5 amp transformer.wt more other devices are required to build its charger.or how can it be charged using home made charger,plz reply soon.i want to use it as inverter

  82. Seetharaman

    Hi Aswin you can use 8550 instead of BD140.

  83. hey there. I would like to try this circuit. I got all the parts expect BD140. Its nt available in any of the shopes in my area. I also tried for 2N2905,i think its my bad luck that it is also not avail. So plese tell me some transistors that can be replaced in the place of BD140. I hope u will reply me soon.

    Thank you

  84. Seetharaman

    Hi Roshan kindly inform me which circuit you are following so that i can give my comment.

  85. Gaurav Jindal

    circut of emergency light with ac 220v regience use

    not use transformer ok

    reply plz

  86. Sorry Seetharaman, shorting the collector and base makes the LEDs glow when connected to the mains. Otherwise it will be off. Do I need to change the variable resistor to 4.7k.?

    I did correctly..I took, left as emitter, center one as collector and the right most one as base…

    Do you have the pcb layout of the modified version of the circuit.?

  87. hello Seetharaman, i modified the circuit as on your comment. But what happens now is, when i connected to main power supply, if i short BD140’s emitter and collector, the leds glow, other wise it will be off…if i remove from mains, it wont glow, even if i short those terminals.

    What is wrong…?

  88. One more doubt…I am basically new to electronics. You have said that you had to forward bias the transistor T2, which is BD140. How did you do that. Did you replace the 1K resistor to 560ohm resister for this purpose?

  89. Hello Seetharaman,
    thanks for the quick reply.
    In the comment of December 29,2009, you have referred to a ‘common negative’ ..Is that the common ground of the ‘lamp section’?

  90. Hello, I have tried this circuit. But didn’t work. I don’t know why. Please help me correct it. Following are the status of my circuit:-

    1) after assembling the circuit and connecting the battery, the leds glow. but, if i connect the main power supply, the leds turn off. But if I short the 1&2 or 2&3 terminars of BD140, the leds starts glowing.

    2) After the first time, the leds are still off even after disconnecting from the mains. But shorting the terminals of the BD140 turns it on.

    3) I dont know whether the battery is charging or not.

    4) When I checked the voltage across ‘anode of D1 and R15’ or ‘cathode of diode D3 and R15’, the voltage shown in the multimeter is very low.

    Is there something wrong. Please help.

  91. Seetharaman

    Hi Imran you can use 2N2905 or the recent 8550 transistor. choose ZD1 as close to 6.8volt as possible.

  92. I want a circuit to illuminate a lamb and if cut off it switchs another lamb autumatically

  93. enersystec

    This is good circuit, we will try to build a few samples for evaluation.

  94. Hi Seetharaman, Can I replace BD140 PNP transistor with any other transistor? I didnot find this in my local market. Please Help me!!

  95. sir,
    i want to add a buzzer which will make sound whenever current is going and coming(like an inveter).Please give a repley

  96. Seetharaman

    Hi Ravi you can use 12-0-12 1Amp, use a good heat sink for LM317 as it has to dissipate extra 3 watts.

  97. Can I use 12-01-12 1A transformer for the 6V 4.5Ah SLA Battery?

  98. Seetharaman

    Hi Sandy Go ahead constructing the modified version. you are sure to suceed.

  99. hi
    friends this sis sandeep i am planning to start this project on my own. I need all ur help to complete successfully

  100. Achin Jain

    Respected sir,
    I am a student of engineering, 3rd year
    sir i was going through with the circuit diagram and wanted to work on it, sir i want to know what exactly Automatic means in this project i mean what is the process of its charging and how does it work. i really wants the complete informations related to this circuit in detail sir i’ll be highly thanks full to you if you reply me for all of my queries and asks i want your support for it because this projects is very much knowledge able for me please reply me on my mail address i.e

    Thank you

  101. hi sir…..i would like to know how much does constructing this full project roughly cost? because im planning on doing this project as a low cost product…

  102. i want to know how it will stop charging after full charge??
    please write how voltage changes and all that for working of this ckt.

  103. Seetharaman

    Hi Patrick no modofication is required you can use12 volt 500mA transformer and 6 volt 4AH battery.
    For good brightness use hi bright white LEDs. Normally 12 LEDs are sufficient. if you fell it is not then add one more BD140 with 12 more LEDs with will be equivallent or better than 11watt ES lamp in illumination.

  104. patrick vaz

    Hi Admin,
    I made this circuit, but the Brightness is very poor, if u could prepare a circuit which would house about 50 to 60 leds would really appreciate.
    Thanks for the help

  105. Hi seetharaman
    subject: 100watt sub-woofer
    i shorted R9 & R10 the temperature of transistors decreased but Q7 is getting hotter than Q5 why ?

  106. Sir,i want to make this circuit with 24 led’s. please tell me what modifications are required for making this? tell me all changed resistors values. and also tell that,with lead acid battery of 6v 4.5AH,how many hours it will give light? plz reply soon.

  107. i am having 14.4 v, 4Ah li-ion rechargeable battery. i need to glow more lights for more hours.tell atleast the lighting circuit.

  108. thank you for the reply. i need wattage of all the resistors used in the circuit.

  109. Hi seetharaman
    subject: 100watt sub-woofer
    i shorted R9 & R10 the temperature of transistors decreased but Q7 is getting hotter than Q5 why ?

  110. seetharaman

    Hi Sunny You can use D size torch cells will give you 500mA hour. That is if you draw 50mA from it, will work for 10hours. Normally the high bright white LED requires around 25mA at 3volt. you may require around 6nos LEDs for enough brightness to read using as a table lamp. That is 300 mA the lamp may work for a maximum of 2hours only. think of alkaline cells quite expensive. think of solar rechargeable lamp?

  111. Sir,in my village there is too much problem of light. So i want to make a LED LAMP which i want to light up from a dry battery. Because in night we have much diffculty in studying by using oil lamp or candle. So please tell us how to make led-lamp by Buying what materials from market.

  112. seetharaman

    Hi Pradeep you can use but the charging circuit has to be modified. The transformer to be replaced with 2.5 amp rating. A power transistor to be added to LM317 IC as it can handle a maximum of 1.5 amp only. R16 to be changed to 2 ohms 20watts.

  113. can i use 6v 9AH battery for the circuit? what are the things i should change? in the above circuit what is the wattage of resistance used? what will be the power output of the circuit?

  114. seetharaman

    If 0.5amp is flowing through 16 ohms resistance then the power dissipation by that resistance is Isq X r = 0.5 X 0.5 X 16 that is 4watts dissipation so higher wattage is preferred hence 5watt is used. If you use a lower wattage resistance less than 4 watts it will get cooked up.

  115. why we use the 5W resistor?what will the effect by using high wattage rating of resistor?

  116. seetharaman

    yes it will improve, instead of 12 hrs it may charge in 8hrs or so.

  117. if i use 1amp transformer will the battery get charge quickly??

  118. how much time it will works when battery is fully charged?

  119. can i use 9-0 v 1A transformer for the above circuit????

  120. can i use 9-0 1A transformer for the above circuit????

  121. can i use 9-0 1A transformer for the above circuit

  122. can i use 9-0 1A transformer for the above same circuit???

  123. seetharaman

    the battery will get heated up and it cycle life will come down drastically. normally lead acid cells should work for 500 charge discharge cycles. by over charging, and charging above manufacturers recommended level and deep discharging the batteries will get their life shortened.

  124. if i give more than 1.35 ampere current to a 4.5AH battery what will happen???

  125. Seetharaman

    Dear Saravanan with 7AH battery it should work for 45 mts to 1hr. Check with a fully charged battery. Check whether the built charger is capable of charging at the rate of max 2.25 amp at 12 volt. If not the battery will take a very lon g time to get charged.
    Try the above checks and give a feed back for the solution.

  126. seetharaman

    Dear Saravanan
    You can use a battery which can sustain for the required hours (battaery AH capacity) say in your case the battery is 12volt and watts is 50 if the inverter efficiency is say 80% you require 60VAH that is 12 volr 5AH battery is required. say for 5hrs you require 25AH battery is required. you have to use a charger suitable for the battery, that is 7.5 amp charger. as the built in charger of the inverter will not capable of charging.

  127. saravanan

    i am working in mnc company.we are seperately installed 50w inverter ( output 1) 230v ac 2)12v dc ) .main is on normal working cotinusely on. if power is cut the inverter mode is on. light is working inverter mode. it will back up 20 miniuts. if cotinues working 1 hour battery is try.customer was very un working inverter mode only 10 miniutes and then cut off automatically. if power will come then working normal operation. plase give modulation circuit for above problem.

  128. saravanan

    i want automatic cut off circuit for 50w will be cut off after 10 minits ( if power cut inverter mode is on )

  129. seetharaman

    Hi Aji yes you can use. connect the base of BD140 through a 220 ohms resistance to negative by using a switch. by the flip of the switch the light will glow during charging.

    Hi Mahesh modify your circuit as per the modified version it will work.

  130. hi, i’ve tried this circuit bt i didn’t get result. actually i confusing at bd140 transister i.m not getting output from bd140 why? i tried as like the same above circuit onlr bt i didn’t getting output. plz kindly inform how to connect the bd140 circuit.

  131. Thank you sir for your kind reply.I’m very honoured to hear from a great person like you.Sir,Can we use mains for charging as well as lighting purpose simultaneously?.I’m asking this kind of questions becoz i’m not familiar with electronics since i’m an IT student.But i like to do in electronics section..

  132. seetharaman

    Hi Aji you can use 2200uF. For R16 you may use 4.7 or 5 ohms resistance 5 watts so that the battery charges within 12 hrs from discharged level. kindly refer modified circuit of this.
    Automatic LED Emergency Light Modified.

  133. hi guys,,i tried to make this circuit.But there are many problems with my circuit.I have got 2200uF capacitor instead of 1000uF.Resistor with 16ohm resistance is not available to me…Is there any problems with these.Whether this problems affect my circuit
    Please reply..

  134. sir
    do you includ low voltege discannect circuit? please reply.

  135. seetharaman

    Hi John one D882 is for invertor and the other one is for voltage regulator for charging the battery. C9012 & 14 are for auto operation you may check these transtors they are PNP and NPN transistors. do cold check on all these transistors.

  136. Sir,
    I have one CFL emergency light of “Champion make”. This utilizes 2nos of D882,1no of C9012 and 1no of C9014 transisitors and other components.My problem is that, when mains supply is resumed, the light does not “cutoff” automatically.what could be the problem sir? Please give me a solution and circuit diagram if possible.

    Thanking you sir,
    With regards,

  137. Faraz Khan

    I want these requirements
    1) DC Output
    2) 0 to 45 and -45 to 0 Volts
    3) 5A on both channels
    4) It must be transformerless.

  138. seetharaman

    Hi Faraz Khan Can you give the full DC side requirement, whether regulated what is the voltage etc.

  139. Faraz Khan

    Hi Guys i want to know that how can i request here. I want to make a transformerless power supply for my projects. I want a supply that can provide me 3A currents both in positive volts and negative volts. For this i searched all supplies which uses a transformer but those transformers are quite expensive.

  140. seetharaman

    Hi Faraz Khan R15 you reduce to 680 ohms. from each BD140 base you connect one no. 680 ohms to negative rail. emitter of all BD 140 to positive supply. collector through 12LED inseries with 100 ohms each to negative as the above circuit.

  141. Faraz Khan

    Hi Seetharaman So i just have to place 680 ohms resistors in between each base of BD140s and leds circuit to individual collectors. Is it correct?

  142. seetharaman

    Hi Faraz Khan You can use 3 circuits of 12 leds driven by its own BD140. That is connect all the three BD140 emitters together. base through 680 ohms from each BD140 base to -ve rail. 12 Leds as above to each BD140 collector. this will enable all the three BD140 to share the current equally.

  143. Faraz Khan

    Hey Thanks SEETHARAMAN. I’ll check it. Another question i want to ask that i want some leds about 36 in number. I know about the BD140 that it will not handle the current so i guess to place 2 more bd140 in parallel to the first one, which will make current divide, accordingly. Is it OK?

  144. seetharaman

    Hi Faraz Khan use an electronic sounder (phezo electric) in parallel with diode D5, +ve of the sounder to cathode and -ve to anode of D5. When the battery is getting charged the sounder supply is reversed (you get around 0.7volt). once the battery is fully charged T1 switches on the battery will supply sounder around 4 volt for it to sound. If dont want negative voltage of 0.7 across the sounder add a diode inseries with the sounder to block negative voltage.

  145. Faraz Khan

    Hi, Every One. I want to insert a buzzer alarm in the circuit.
    i want the buzzer, alarm me every time the battery get full charge. At every alarm signal i will switch off the ac main for Power Saving.

  146. seetharaman

    Hi Colin yes i agree with you. But with the present design, if you use amber LEDs you can use two of them in series. with white LEDs the voltage requirement is 3 to 3.2volt connecting them in series may work, at full charge of the battery, but with discharged battery may not glow at all. If you use 4volt batteries the efficiency can be improved or 12 volt with 3 LEDs in series.

  147. seetharaman

    hi devang you email me i will reply you in depth.

  148. devang manseta

    hey can any one explain me tha working of thid circuit?
    Mr.anand please try

  149. seetharaman

    My id is any way i will mail you in your id. i have already devoloped few circuits with pcb etc which are in use, i have plans to submit soon to Circuits Today for publication.
    Hi prshanth the standard emergency light PCBs are available in the market using 7/11Watts 2 pin energy saver tube with 6 volt gel cells. it can be used. the charger circuit need not used.

  150. Dear Seetharaman,

    Mails are bouncing back from your ID.. so please let me know any other id or send the circuit to my email id –… Also please send me any LED lights working ini the main AC directly.. i think we can save energy a lot if we can replace our existing ‘bulb’ with these LED leights.



  151. Prashanth

    This circuit to good & working fine.
    Is it possible to connect CFL lamp?
    How to hook up inverter circuit to this circuit?
    please let me know.
    If you have any simple inverter circuit please share.


  152. V G KRISHNA

    Dear Seetharaman, Two mails sent to your above id failed to deliver.Kindly send the modified circuit to me also at and also kilndly send the prototype developed by you with a number of LEDs for the LED light through Mains. Regards and Thanks. V GOPALAKRISHNA.

  153. Seetharaman

    Hi Anand LM317 and T are the same in TO220 package. P is for full plastic package and pins as per T. D2T is SMD package, K is TO3 package similar to 2N3055.

    Type TO-3 TO-220 TO-220FP D2PAK
    LM117 LM117K – – –
    LM217 LM217K LM217T – LM217D2T
    LM317 LM317K LM317T LM317P LM317D2T
    Hi Anand send me a email I will mail you my modified circuit.

  154. Dear VG Krishna,

    Thannx for ur suggesions.. could you pls tell me wht is the difference in the pins of LM317 & LM 317T?? i found both are same in the net.. pls let me know , necoz im using 317T.



  155. Dear Seetharaman,

    Could yuou please send me the revised circuits with necessary changes in the components value?? i want to assemle the same from begining in a new board. If you post or send the revised circuit thru email to me.. tht will help me a lot and also there wont be any confusion for me.
    regards, Anand

  156. devang manseta

    i need your help!
    please anyone who reads this and is aware of the problem please answer my question!

    i have tried the whole circuit
    leds glowing well
    it glows even wen i switch off da mains
    i dont know wat to do?
    plz help
    n how do i rectify the batery is getting charged or not
    reply as soon as posssible!

  157. Dear Seetharaman,

    Thank you for your reply.. i will recheck the same and get back to you if any help required.



  158. V G KRISHNA

    Thankyou Seetharaman for your kind prompt reply.
    Regards. V.Gopalakrishna, Hyderabad, India.

  159. seetharaman

    Hi Krishna you can provide the switch between BD140 emitter and battery positive. To improve charging current as I have mentioned earlier reduce R16 to 4E7 5Watts. You can reduce it even to 2.2 ohms if required. For charge indication use BC158 transistor. connect its emitter to D5 R16 junction base through 100 ohms resistance to R16 ZD1 junction. collector through 470 ohms and an LED (I prefer amber)in series to T1 (BC148) emitter. When ever there is a higher charging current through R18 the LED will glow brightly and as it tapers off LED will become dim.

  160. V G KRISHNA

    Dear Seetharaman,
    I assembled the above circuit. All the 12 LEDs are glowing alright when I swith off the mains but it was taking 5 to 6 seconds for the LEDs to light after the power switch off. Subsequently to day, I made the alterations suggested earlier by you by reducing R15 to 560 ohms,connecting 560 ohms resistance between the junction of D1 and R15 to common negative and reducing R16 to 4E7-5watts. Upon this it is working very well and light is coming within a fraction of second. Thanks a lot to you. Now I request help from you.

    No switches are provided in the original circuit. So kindly suggest for the benefit of me as well as to all users as to, where to provide a switch for the emergency light portion to switch on/off the LEDs at will, while keeping the set plugged on to mains on.
    Where to provide an LED light to indicate that the set is
    under charge.
    Further more I want to share with you that as per the original circuit, when I measured the voltage at the two terminals before connecting to the 6v 4ah battery, it was only 0.87 DcV and amps is zero. After the above alterations, it has improved to DC V 5.20 but when I mesured the DC amps with multimeter set under DC 10 Ah, it is still measuring/playing between zero and 0.01. I am at loss to understand whether it is sufficient to charge the 6V 4 Ah battery. The preset 2.2k is adjusted to maximum by me.
    Kindly advise. I am verymuch interested in the circuit and Thanks to CIRCUITSTODAY for providing the circuit.
    V.Gopalakrishna, Hyderabad, India.

  161. seetharaman

    Hi Anand Please check the polarity of the zener diode. If it is connected as forward biased diode only this can happen. By reversing the zener will solve all your problems.

  162. V G KRISHNA

    Dear Anand, I assembled the above circuit and am happy on the success of it. Thanks to CIRCUITS TODAY. All the 12 LEDs are glowing rich. But two things what I observed are
    1) the LED lights are not glowing based upon the supply from the transformer alone, unless i) we attach the 6V 4 ah. battery in the circuit, making thus the circuit comlete,and ii) only after the mains supply is put off. It will be convenient, if it is made to glow when power is available (work as a night lamp) and auto changeover to Battery in case power goes.
    2) It is taking a few seconds (5 to 7 seconds) to the LED lights to glow, over the switch off of the mains. I think, this can be improved upon based upon the improvements suggested by Sri Seetharaman on Dec.29, 2009 above. Overall the circuit is good. For increase in the light, I want to increase the no. of LEDs also , as suggested by Sri Seetharaman abaove. I am getting the maximum voltage past LM 317,after adjustment is 6.2v. Hope this will be suffcient to charge the battery. For your problem, please check up the assembly of your circuit for any ‘short’ connections and for correct pins of the transisters 1 and 2 etc.etc. Pins are different for LM 317 and LM 317 T. GOOD LUCK. V.GOPALAKRISHNA, HYDERABAD, INDIA.

  163. Dear Seetharaman,

    I tried this circuit exactly what you mentioned in the Circuit. But I found following problems

    1) The output of LM317 can be set maximum up to 2.94 v by adjusting the potentiometer.
    2) Out put voltage of the battery charging end shows Zero.
    3) I have connected 12 LEds and only 6 or 7 led’s are working and that also not bright.

    Pls suggeste me wht will be the wrong.

  164. seetharaman

    Hi Masandhie Since you are using 12volt with 20LEDs 20 X 25 is 500mA current and the voltage drop across the trasistor will be 12-3=9volt 9 X 0.5A is 4.5Watts Hence BD140 will get heated up very much and you will be wasting huge energy as heat. Instead use 3 leds in series with 100 ohms resistance in series. with 7 loops (7 X 3 = 21 LEDs)The current will 7 X 25 175mA and the voltage drop across the transistor will be 12-11.5=0.5Volt Hence 0.5 X 0.175A = 0.0875 the transistor will be cool running, the designed circuit is meant for 6volt when we adopt it to 12 volt we have to modify the circuit accordingly.

  165. Masandhie

    Hello Seetharaman
    i have tried the circuit and it work, in my experiment i use motorcycle 12v lead acid battery, 20 led with 3 resistor 27ohm/5w to limit the current and it work,the resistor will only get warm in temperature but the BD140 get very hot (i can put a fan on it but it will increase the battery life).

    can the BD140 changed with other series of transistor which has higher output current?and if it can what series do i had to applied?

    i have tried some series like TIP2955 or 3055 but it fail.



    I salute Sri Seetharaman for his expert and excellent advices being given by him, which I have seen from many a
    circuits. I am a retired (finance) person having interest in electronic hobby projects. Through these columns,I have assembled about two LED circuits which are working excellent. I thank Sri Seetharaman and others who are participating in sharing the ideas with their expert advice. I want more and more such Projects. Thanks to ALL.
    V.Gopala krishna,Hyderabad, India.

    • Dear Sir,

      The first circuit i build is not working. the led’s are glowing even lights hit.also in the presence of mains power. can you guide me through to fix this.?

  167. seetharaman

    Hi Figo Vbeo indicates the reverse break down voltage of the trasistor base emitter junction. Vbe forward bias will be 0.65 volt. R15 is sufficient to limt Ibe. regarding protection You may please send the circuit to Admn to publish it bu which all will be benefitted. thanks

  168. Hello Seetharaman,

    I have two comments on this circuit,

    1. The Vebo of T2 is 5V, so we need add a 9V zener from base of T2 to GND.

    2. I have a sketch of discharge circuit to protect the battery, but I do not know how to share this circuit here.

  169. Dear,
    A good project. I will try.But what be the possible wattage of this circuit, I mean when LEDs are on, How much current required or what energy they consume.

    god blis


  170. Samba Damerla

    Thanks SeethaRaman,
    I will search Ni-MH charger circuits. If possible could you please let me know once Adm Circuits publish a circuit for my requirements.

    By the way is it work if I replace present charging part of the circuit with Ni-MH charger (i mean can i still use BD140 if I replace the charging part of the circuit).

    Thanks & Regards
    Samba Damerla

  171. seetharaman

    Hi Samba for Nicad or NiMH batteries constant current charging is important and NiMH cannot be trickled successfully even at 1/40 th of rated current for 40 hrs, charging NiMH are complicated. Standard designs are available in the net. you can use Ni-MH battery charger using LT4060 appeared in Circuits today. Lots of modifications are required to the present circuit. I will request Adm Circuits today to publish a circuit to meet your requirement.

  172. Samba Damerla

    Hi Seetharaman,
    I want use 4AA 1.5 V 2500mA rechargeable cell instead of Acid battery. Please tell me how to change the circuit. Its ok if we reduce number of LED’s to 6.

    I want this because I want to setup this as buld and sit in a bulb holder.

    Samba Damerla

  173. Hello Seetharaman,

    Shenzhen is not only a Battery city, hehe,

    Thanks for your quick response, looks like you are also a professional guy in electronics design,

    Let me check the circuit again and to see how to improve this circuit to make it perfected.

    In my mind, it seems required a voltage comparator to detect the battery voltage. I will add my comments here,

    if you have any good ideal, please also share with us here.

  174. Samba Damerla

    Hi Seetharaman,
    I don’t want to use 6v 4.5 AH lead acid cell, instead of that I want to use four 1.5 V, 2450 mAmp AA rechargeable cell. Its fine if we reduce number of LED’s to six.

    Please advice me how can i change the circuit. I want this change to make a rechargeable torch or a rechargeable bulb (which can sit in a bulb holder). Incase of bulb I don’t have a chance to use heat shrink.

    Thanks and Regards
    Samba Damerla

  175. seetharaman

    Hi Figo from the Battery city, Charging is taken care, the terminal voltage is limited to 6.8Volt and the max charge current is <30%.{ fault in LM317(short)}. 6 volt 4.5AH lead acid gel cel. (Charging with constant voltage and initial current <30%). only discharge is not taken care yes voltage less than 5.25volt is end point of 6 volt battery(infact no useful energy is available below this from the battery). hence at 5.5 volt the discharge should be cut off(load should be cut off). an additional sensing circuit to be provided to cut off the load.
    Thaks for your critical view. you may also suggest your improvement in the circuit.

  176. Hello Admin, This is Figo come from Shenzhen of China, Im very interesting in this circuit, but I have some concerns:

    1. How to limit the discharging current to make the battery will not be damaged due to over-discharging?

    2. How to limit the charging current to avoid damage to battery due to a higher chanrging current when some fault occured.

    3. What type of battery we can used on this circuit? such as Lead-acid battery, Ni-Cd or other type of battery. becoz different battery has different charging character.

    Hope get your response soon,
    Also hope we have more discussion here with guys in the world.

  177. Masandhie

    Thanks a lot SEETHARAMAN that’s helps me a lot 🙂

  178. seetharaman

    Hi Masandhie Sorry I have missed, yes you have to increase it to 13 volt zener with the same wattage(0.5watts)

  179. Masandhie

    What about the zener diode ZD1, does it function to limit the charging to battery?is it necessary to change the zener diode with the higher value?

  180. seetharaman

    Hi Masandhie yes you can use 12 volt battery and replace with 12 to 15volts transformer. set the voltage to 13.8volt. You can use 3 LEDs in series in each loop(total of 36LEDs). You can increase R3 to R14 to 150 ohms. You cannot paralllel all the LEDs and connect a common single resistance. Due to manufacturing spread the LED with least resistance will try to pass high current since no limitation, will blow. Hence you have to limit the current through individual LEDs (safe limit of 25mA each in this case)when connected in parallel. Please do not forget the good heat sink for T2.

  181. Masandhie

    if i use a 12V lead acid battery that will flow to the Emitter of the T2 is it ok if i use a 15V input from my 1A transformer and can i change the ZD1 with 12V or 13V for charging the battery?

    i try to use a 15ohm 5 watt to replace the r3…r14 wich will be connected paralel to my 25 LED…hopefully the current consumption will be 500mA

    maybe this will help

  182. seetharaman

    Hi Lucky you can add similar circuits (with R15, TR2, LED1 to LED12 and their series resistances R3 to R14) 6 sets in parallel. So that you can drive 72 LEDs. But the battery will last for ony 2 hours.

  183. Thanks, Seetharaman. i check it. Can you send me a 70 LEDs circuit configuration.

  184. seetharaman

    Hi Lucky Kindly check T2. For BD140 center collector left emitter and right base. During power on base will be more positive than emitter hence T2 gets reverse biased, hence T2 will not conduct hence no illumination of LEDs.

  185. its not a complete circuit, because i built it but it does not works automatic. when supply ON, then its glow and when suplly is disconnenect then its also glow… Why??? whats a problem brother? tell me. plzzzzz

  186. seetharaman

    Hi Sathika you can add similar circuits in parallel, that is from BD140, 12 LEDs and their current limitting resistances in series.(T2, LED1 to 12 and R3 to R14, for each additional 12 LEDs you want to connect). Ensure the battery is also capable of handling the load. the present battery with 4.5AH capacity, 36 LEDs will glow for more than 4 hrs non stop.

  187. A good project. I will try.But what be the possible wattage of this circuit, I mean when LEDs are on, How much current required or what energy they consume.

    An emergency light is a battery-backed lighting device that comes on automatically when a building experiences a power outage. Emergency lights are standard in new commercial and high occupancy residential buildings, such as college dormitories. Most building codes require that they be installed in older buildings as well.
    Modern emergency lighting is installed in virtually every commercial and high occupancy residential building. The lights consist of one or more incandescent bulbs or one or more clusters of high-intensity light-emitting diodes (LED). The emergency lighting heads are usually either PAR 36 sealed beams or wedge base lamps. All units have some sort of a reflector to focus and intensify the light they produce

  188. Thanks Seetharaman for your quick reply. but appreciate if you can tell me how can i add more LEDs (30 or 40) in to this same circuit (With 6v battery). what should i change? It’s great if you could attach a rough diagram. but can’t see the facility with post reply section here.

  189. Seetharaman

    Hi sathika. yes it is for a 12volt supply. this reply is for md arifuddin sheik’s quiery. for 3 white modern leds (available in india)you require 3.2 X 3 9.6 volts at 25mA. with 100 ohm current limiting resistance and the voltage drop across transistor a 12 volt DC supply is required. i am using this circuit with my existing solar lantern with built in 7 watt energy saver tube’s battery supply.

    I’m very very new to electronics & still i’m lerning. so pls explain how we can attach 3LEDs in series with same setup(anyway circuit is having 100ohm with 6v bat). or are you planing to use 12v battery supply?

  191. seetharaman

    Hi you can use 3 LEDs in series. hence you will have a total of 48 LEDs glowing(lots of illumination)still with the same current consumption of appoximately 250mA. You require a series resistor of 100ohms only. With 12 Volt 4.5AH battery you can have a minimum of 16 hrs non stop run. better set the open circuit voltage at charging terminal to 13.6 volt which will be just correct for lead acid gel cell.

  192. Arifuddin Sheik

    How many hours of decent backup will we get using this circuit. If battery drains below 10.2V, the life of battery may decrease. This circuit needs that protection of low voltage. If we use a 12V battery, what all changes we have to make to R16, diode and variable Voltage regulator. We can increase the LM317 o/p to 13v. But do we need any other changes apart from the LED current limiting resistors.

    Arifuddin Sheik

  193. vikas billa

    here in the above circuit they used 14 leds,each led takes 30mA so 14*30mA=420mA.The ouput current from transformer is 80mA is drop across transistor.

    Now my question i have to connect 40 leds…so what will be the output current of my transformer .whether i have to change the battery..

    please suggest me

    • admin

      Reply to Vikas Billa
      Current rating of Transformer X1 must be 2A.
      the 4.5 ah battery is enough, but back up time will be less.
      also, fit a small heat sink to BD140

  194. vikas billa

    hello i want to use 40 leds suggest the corrections in the circuit

  195. thanks for makin such a ckt….it is really it was our project finally we got good marks…

  196. After a long gap in electronics I have built this circuit.
    I have few spare LEAD-ACID batteries and was looking for a circuit to charge those (6v, 4.5 AH).

    I have built only the charger part. Output voltage is 7v and the charging current is – 200ma. I will test the charger with a battery in the next few days.

    Next, I plan to build the led part. I bought few small led’s and one 3W PRO LIGHT LED( approx – 3$). Planning to build few led projects to prepare for the power cuts in the coming summer season here.

  197. Seetharaman

    Thanks for the very useful domestic gadget during present days of power cuts. To make the lamp work I have to forward bias transistor T2. I have reduced R5 to 560 ohms and connected a 560 ohms resistance between junction of D1 & R5 to common negative. Which made the LEDs come on when power failed. By reducing R16 to 4E7 5 watt the charging could be improved to over night in my light.

  198. how to make emergency with maximum white led in a 6 volt batt

  199. hello..i will like to have more info n details based on AUTOMATIC EMERGENCY LIGHT, want to know the function and work of each component used, plz do help i need it for my final year project thanks
    pls e-mail to my inbox do appreciate

  200. hello..i will like to have more info n details based on this project, want to know the function and work of each component used, plz do help i need it for my final year project thanks
    pls e-mail to my inbox do appreciate

  201. If I use 12v 9A battery, what changes are required in circuit?
    1. R3-R14 resistor should be 1k each. Am I correct?
    2. How much time will be required to charge 12v battery?
    3. Will tranformer of 9v 500mA charger 12v battery? If not should 12v 1000ma transformer be used.

  202. what can use in the place of BC548 , cause I can buy this can something take place in this place ,,,,,,,,,,,,,,,,,,,,,can help me please
    I’m making this ckt now plz

    • admin

      BC548 can be replace with transistors like BC148, BC107, 2N2222 etc

  203. what can use in the place of BC548 cause I can’t by this . can help me please ………….I’m making this now……………….

    • admin

      BC148, BC107, 2N2222 etc can be used instead of BC548

  204. Good ckt but will you please give circuit diagram for same emergency light using npn transistor

  205. hi can i use the BC547 in the place of BC548 cause the store have not this BC548 Please Please I need to know ,I’m making the ckt now………….

  206. rohit mukherjee

    hey friends plz help me I am having a problem with this circuit,when i connect the battery the 16 ohm resistace gets burnt the led blink for sometime and then it goes off the resistance gets burnt completely.plz help Thanks

  207. hello dears i want a similar circuit with 12v & simple bulb of 50w because i want much more help THANKS

  208. how much time will it need to fully charge befor it stop charging?

  209. twits4twats

    Assuming that the LED’s you are using are standard white LED’s with forward volt drop of 2V and current consumption of 20mA. General rule of thumb for LED’s is to limit current to 10mA. This will maximise the life of the LED. For R3 – R14, if a 12V supply is used,use a 1K resistor and therefore for a 6V supply use a 0.5K resistor.

    The circuit was designed for 12 LED’s and not 24.

    T2 (BD140) can switch up to -1.5A so this won’t be the problem (24 x 0.02 = 0.48A).

    How have you connected the extra 12 LED’s? If they are just placed in series with the existing LED’s, so you have 2 in every chanel, then this fault is most likely caused from the resistor R3 -R14 values. If they are connected like this, try changing the values to 0.2K each.

    If the extra LED’s are connected in parallel to the original ones, in other words there are now 24 seperate channels, and the resistors are all about 0.5K each, the chances are that your battery cannot handle the load.

  210. What will happen if i use a 12v rechargeable battery instead of 6v battery

    • admin

      If you use a 12V battery instead of the 6V ; Circuit will not work properly,
      Battery will not get fully charged,Double amount of current will flow through the LEDs during battery mode (can cause damage to LEDs).

  211. i got 12V 7A battery so can any one pls modify this circuit for it and i need more bulbs too pls help me

  212. dEAR TAHIR
    CHAKE 2.2k vr1[preset] or short by 1k2resistance

  213. peter nyondo

    Can’t i use any other pnp transistors(same ratings) in place of BD140. in have several pnp transistors in stock.

    • admin

      ok its quite fine if the ratings are same

  214. Kichler Lighting

    This is great information for anyone whoever wanted to know what the inside of a light looked like.

  215. i assembled this circuit and use 24 led 5mm but problem is that all leds became dim after a few seconds. if any one has suggestion, please let me know

  216. There is promble of charging of battery it takes 20-36 hrs

  217. S Mukherjee

    What will happen if i use a 12v rechargeable battery instead of 6v battery? should i have to change any components? if so then can u give the exact circuit diagram. Im new to electronics and need experts help to make this kind of hobby things.

  218. Dear,
    A good project. I will try.But what be the possible wattage of this circuit, I mean when LEDs are on, How much current required or what energy they consume.