Dual Adjustable Power Supply Circuit

Description

Power supply is a circuit based electronic device that supplies the needed electrical energy to an electrical load. Power supplies can also be named as electric power converters as they are used to convert electrical energy from one form to another. Power supplies are used in everyday consumer devices and PC’s. In such devices the power supply unit is inbuilt along with their loads. The power supplies that we are going to discuss are more discrete and are useful for simple projects and minor electrical applications.

The aim of the dual adjustable power supply circuit is to provide power for other projects that require a dual (+/-) adjustable power supply.

This is the circuit diagram of a dual adjustable power supply using IC’s LM 317 & LM 337. LM317 is able to deliver a maximum of 1.5 A at a range of 1.2 V to +30V. LM317 is a positive voltage regulator and LM337 is the negative compliment voltage regulator IC of LM317. The LM317 IC is a 3-terminal voltage regulator that is designed to supply in excess of 1.5 Amps of a DC output voltage range of (1.2-30) Volts. These IC’s also have a special TO3 package and if assembled with a large heat sink (HS07051 preferably), the power supply can be designed to handle load current to its max. They also have a built in short circuit protection.

Refer: LM317 Voltage Regulator Circuits

Here the circuit is wired to produce a dual adjustable output of ( +15 , 0 , -15 ). The capacitors C1 to C8 provides filtering and ripple rejection. Resistors R1 & R2 controls output of LM317. Resistors R3 & R4 controls the output of LM337. R1 and R4 can be turned to vary the positive and negative voltages. This circuit is a must on an electronic hobbyists workbench.

If needed two LED indicators can also be connected to indicate the positive and negative power outputs. A Blue LED can be connected across U1 and GND and a Red LED can be connected across U2 and GND. The Blue LED can be kept as an indicator for positive power and Red indicator can be kept as an indicator for negative power.

Notes

  1. The transformer should be anything that produces a min of 3 A with (24 0 24 ) output voltage.
  2. The voltage range can be further increased by increasing transformer output within the limits of IC.
  3. Do not connect a load drawing more than 2A at output. The IC,s must be fitted with heat sinks for better protection.

Parts List

ComponentSpecificationName
C1, C2 2200 uF50V Electrolytic Capacitor
C3, C4, C5, C72.2 uF50V Electrolytic Capacitor
C6, C8 100 uF 50V Electrolytic Capacitor
R1, R4 5K OhmsPotentiometer
R2, R3 220 Ohms1/4 W Resistor
D1 to D4 IN 4007 Diodes
S1 SPST2 Ampere Switch
U1 LM317Voltage Regulator IC
U2LM337Voltage Regulator IC
T1 24-0-24 Center Tapped 2 Ampere Transformer
Extra Heat sinks for two IC's , Power Cord, Casing, Wires

Dual Adjustable Power Supply Circuit Diagram.

Dual power supply circuit

 

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3. Dual Power Supply using L165

4.  40 Volts Dual Power Supply

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Author

38 Comments

  1. George Nabil

    YOU ARE AWESOME GUYS
    I’LL MAKE THIS CIRCUIT SOON
    AND THERE IS A LOT OF QUESTION ABOUT CIRCUIT I WANT TO TALK ABOUT IT CAN I ASK YOU SIR ??

  2. Usman Idrees

    Are there any formulas to calculate resistor and capacitor values? if yes, then what are they?

  3. what should we do with open ends of the variable resistors R1 AND R4??….reply fast

    • they are simply 5k potentiometers. one of the ends are connected to c1 c4 junction and the other ends are given as input to pin no 1 of 317 and 337.hope it helps.

  4. Saraii Maute

    If I use center-tapped 12V 750mA transformer, what else in the circuit should I replace so it would work just fine? Please help me. thanks in advance..:)

  5. Hi! Where does the other side of R1 and R4 connect?

  6. hi
    why we use c1 12 parallel? cant use only one 2200uf? also in other side only 100uf one only?
    reply soon……

    • Seetharaman

      Hi C1 is for smoothing + voltage bus(depends on the current load on the bus) and similarly C2 is for smoothing – voltage bus.

      • thank you
        but i want to know is why use c3 and c4 parallel with c1 and c2.

        • Seetharaman

          THe electrolytic capacitors are wound capacitors their equivalent circuit will indicate it contains and inductive component also in series. This makes the capacitor ineffective in decoupling high frequency component in the power supply. to achieve this a low value disc like 0.1 or 0.22 uF or 2.2uF tantalum capacitor used in parallel with high value electrolytic capacitors. you may go through the following link for better understanding
          http://www.intersil.com/content/dam/Intersil/documents/an13/an1325.pdf

  7. Hi can I ask if this would be suitable, I need a supply with +20v DC and -20v DC it is for an audio pre-amplifier, would I still need to use a 24-0-24v transformer or could I use one with lower voltage and also would the transformer need to be such high current?
    Thanks
    Gary

    • Seetharaman

      Hi Gary The audio pre-amps are class A type. They always draw the same current whatever may be the input signal level. for a +20 and -20 volts use a transformer of 15-0-15 volts transformer with rectifiers and decoupling capacitors will give the required voltage. no regulation is required.

  8. Hi there!! Was wondering about the caps. Are they meant to not have a junction on the ground? Having trouble getting the lm337 to work..

    Regards
    Eujean

    • Seetharaman

      Hi Eujean the junctions of C1, C2; C3, C4; C5, C6; C7, C8 to be connected to common GND. The dots are missing. The circuit is correct and will work.

  9. Pingback: dual rail supply and ground

    • Seetharaman

      Hi Normally zero volt reference bus should be connected to ground, where the requirement is both positive and negative voltage like op-amp IC audio amplifiers etc .

  10. hi every one
    there’s something abt that circuit i have used all the components but the output is abt 27.7 -27.7 v insteade of 15 -15
    and i doesn’t starts at 0 v , it starts at 1.6 v

  11. faraz shahid

    how to make the display of power supply digital

    • Seetharaman

      Hi Shahid you can use standard 200mV 3 1/2 or 4 1/2 panel meter modules with its own separate power supply 5 or 9 volt and suitable multiplier and shunt resistance to convert the input to the required 200mV range.

  12. sir
    is there a way to buit dual power supply using only lm 317??

  13. sir
    can we built dual power supply using only lm 317 ???

    regards
    rahul

  14. Seetharaman

    HiRahul With LM317 & 337 YOU CAN USE A SINGLE CENTER TAPPED TRANSFORMER. IF YOU WANT TO USE 2 lm317 YOU REQUIRE A TRANSFORMER with 2 independabt secondaries and 2 rectifier and filter circuits to takecare. it will become 2 independant supplies in sereies.

  15. hi every one has any one assembled this circuit ?? anyway can any one tell me instead of using lm337 can two lm317 be used…???

    • they are simply 5k potentiometers. one of the ends are connected to c1 c4 junction and the other ends are given as input to pin no 1 of 317 and 337.hope it helps.