Transistor Variable power supply 1A, 0-30V

I am going to show you an old circuit that interesting. No ICs, no Zener diode. But it is also a steady voltage.

This is a simple transistor variable power supply project, 0-30V 1A.

Why should we make it?

It is a small circuit, cheap, and buys easy.

Transistor Variable Power supply

How it works

Look at in the circuit includes 2SC1061 and small transistors as a main. It will control the current up to 1 A.

0-30V 1A transistor variable regulator circuit

Circuit diagram of Variable power supply 0-30V 1A using transistors

Also, another a few components. You can adjust the output voltage with VR1.

Thus, It is suitable for learning a basic variable regulator.

If you want higher current and efficiency. 

What is more? 

The details

The IC (integrated circuit) is so famous in this electronic age. Because they are small, easy, and maybe cheaper. But someone may not like it.

They like the transistor circuits. Because when it is broken. We can repair it by changing only a few parts. So it so saves money.

But if the IC circuit. We need to change the IC.

Perhaps it is expensive or we cannot buy it at the local stores.

This circuit is the series regulator mode so it has high efficiency.

First of all, the AC-main comes to the circuit. It is flowing to the DC unregulated section. They include T1,D1,D2,D3,D4 and C1. You can read more about DC unregulated power supply.
Now the voltage across C1 is about 33VDC.

Then, the little current comes to the base of Q1 through R1—limiting current resistor—. Since Q1 and Q3 are The Darlington-pair emitter-follower transistors. It makes Q1 and Q3 are working with high current.

Some current passes R5 to D5. The voltage across it is the constant voltage, 0.6V.

Even a little current flows through R3, VR1, and R4. They are a voltage divider circuit.

VR1, adjust the output voltage. When we adjust VR1 to control a bias current of the transistor Q2-BC337. It will control the bias current to the base of driver transistor-Q1.

To drive Q1(power transistor) runs in the full current, with an output voltage as we adjust, 0V to 30V.

Recommend: 0-20V 1A Adjustable DC Supply

The Shopping lists

0.25W Resistors
R1, R2: 10K
R3, R4: 100 ohms
C1: 2,200µF 50V Electrolytic
C2,C3: 100µF 50V Electrolytic
Q1, Q2: BC337, 50V 800mA NPN Transistor
Q3: 2SC1061 or TIP41 or H1061 or MJE3055, 50V 4A NPN Transistor
D1-D5: 1N4002, 100V 1A Diode
VR1: 10K Potentiometer  
T1: 24V 1A transformer

Making this project

First, assemble all the components into the PCB layout below. Although it is a small circuit. But always be careful.


PCB layout of Simple Variable power supply 0-30V 1A

Second, Enter the power into the circuit. Then uses a voltmeter to measure the voltage output.

Third, adjust the VR1, then look at the meter should change as we adjust it.

Fourth, Test to connect the load to the circuit, The output voltage should be a constant voltage, does not change.

Do not forget. The Q3-C1061 must hole with a proper heat sink.

Here are a few related posts you may find helpful, too:

Related Posts


I always try to make Electronics Learning Easy.


  1. Leen Mae


  2. Ivan Jules

    she is raging coz it doesn’t work for her. admin, what should i change to achieve 3amps?

  3. Ivan Jules

    I need to make a transistorized one, without ic’s

  4. jeff portez

    meron akong mas simple na diagram,nkopya ko lang sa shop noong nagojt ako,subok na po ito,ngamit ko na sa pagcharge ng cp,katunayan ang dami ko na nbenta,kaso nga lang d ko dala ngayon yung kopya iniwan ko samin,dulot ng trabaho ko,eh baka kasi mawala,maybe by december ipost ko sa fb ko pagmakauwi ako,same components po yung c1061

  5. jeff portez

    i have a simple diagram of c1061 which ive gotten from my ojt time,simple,but effective,i have copy,left at our home

  6. juanderful

    Hi, i just wanted to ask, how can i adjust the range from 0 – 30V to 0-15V??

  7. van boni

    Will it work too for a tranformer that gives a current of 2 Amps? Asap. Thanks 😀

  8. mark gil

    hi jeff portez,
    pwedeng kunin ung diagram nung circuit mo?

  9. MR OHM 1970

    Hi Van Boni..Yes The Transformer will Take The Current it will need!!! You will then have a 2-1 or 1A of Headroom

  10. cody

    hello Sir … does this circuit really work? plss reply asap … thank you

  11. Mahar Falcutila

    May I ask what is the secondary rating of the transformer?

    • Hello Mahar Falcutila,

      Thank you for visiting and interested in this project.
      It is 24V 1A transformer.

      If your project is successful. Don’t forget to share it with me, thank you.

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