Simple Variable power supply circuit 0-30V 2A

If you are beginners. You want a simple variable power supply. That can give 0-30V 2A output.

This circuit may be best for you. Because it has a few parts, small, and cheapest. Than others circuit that same power.

The features of this handset are the DC voltage continuously from 0-30 volts. And, apply current up to 2 amperes. And can put easily in a large pro box.

How it works

The power supply is a circuit that is easy to understand. Because there are quite clear components.

I like to study it. If you like me. Let’s see. Is it really easy to understand?

See the image below.

This is a Block Diagram of Simple Adjustable Power supply circuit. Let me explain to you how it works step by step.

This is a circuit diagram. We apply AC line to the circuit to SW1 on/off to the transformer T1 and fuse F1 to protection circuit when too much power source.

Recommended: Working principle of unregulated power supply 

Beginning Variable power supply circuit 0-30v 2A
Figure 1 Beginning Variable power supply circuit 0-30v 2A

T1 reduce AC voltage 220V into 24V 0 24V. Then, the current through to both diode D1, D2 to rectifiers to DC voltage. Next, C1 filter current to DC voltage about 36V.

Related: Learn Fixed voltage Regulator Working principle

There are LED1 to show power on and R1 limit current to a safe value.

R2-100ohms and ZD1-30V are connected together as the 30V steady DC regulators.

The variable resistors VR1 is used to adjust the output voltage between 0V to 30V.  There are transistors Q1, Q2 increase the output current up to 2A.

Also, there is the short-Circuit protection include Q3, R3.

How it builds

The circuit assembly is very simple Because the devices are less Can assemble down on the perforated board. While the power transistor Q3 – 2N3055 is working, will hot so we always use a heat sink on it.

Should use low wattage soldering iron does not exceed 30 watts. The soldering the legs of transistors and diodes we should use the pliers with leg devices Because these devices cannot be very hot.

Adjustment and usage

The prototype works well, have ripple voltage at output lower than 1 mV and the output voltage will drop lower than 0.1 volts

In real usage that although it off, LED power ON will still light up for a moment. Because the LED gets current from C1 that does not discharge fully.

If you want to stop LED immediately. You may move R1 and LED1 to across the secondary of T1.

Then, add the diode-1N4001 series with LED to protects voltage backward which LED may be damaged as Figure 2

The LED will outage immediately when switched off
Figure 2: The LED will outage immediately when switched off

If need to use the dual power supply (Positive Ground and Negative terminal) For testing amplifier OCL.

We change the rectifier section to new, from a Full-wave into the bridge and use the two secondary coil; 24V 2A. Then, apply the negative and positive of each channel to the ground as Figure 3

Making supply is 2 sets with bridge diode and capacitor
Figure 3: Making supply is 2 sets with bridge diode and capacitor

The parts you need

Q2, Q3: 2N3055 Power NPN transistor
Q1: BC548,BC549, 45V 100mA NPN Transistor
D1, D2: 1N5402 3A 100V Diode
D3: 1N4002 1A 100V Diode
ZD1: 30V 1W Zener
VR1: 10K Potentiometer
R1: 3.3K, 0.25W resistor
R2: 100 ohms, 0.5W resistor
R3: 0.3 ohms 10W resistor.

Be careful Components pinouts

Some parts on this have different pins. You need to put it in the correct way only!

Be careful component pinouts on power supply circuit
Be careful component pinouts on power supply circuit

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Salim khan



Hi, Salim Khan
Thanks for your feedback.
You are welcome.

Augusto Principato

Very interesting !

Hello, Augusto Principato
Thanks for your feedback.


simply—–the best!

Hello, walter
Thanks for your feedback.


Hi, Augusto Principato
Thanks for your feedback.


Hi, walter
Thanks for your feedback.


where is the placement of VR1 10k pot. I can not see it in figure


Hi, subodh
Thanks for your feedback.
Please look at the figure 1.
VR1-10K ,


hi is this still uselful with 12 0 12 volts transformer?? can u make using 12 0 12 volt transformer.?


hi, how can i change the output to 3 Amp in this schematic diagram?

Efraem Salcedo

This circuit is great. It works. Thanks!


Hey! Plz explain me! How the current is amplified … Coz , its confusing me! Make it fast, or reply to my mail id. [email protected]


I would like to send me some mini circuits

Hello, Mamdouh
If you still want mini circuits. I will send you the email. Thanks

Jed Frances Ararao

a current limit function would be very nice..anyone can tell me how to add a current limiter function to this circuit?

Hello, Jed Frances Ararao
Thanks to your question. This is a simple circuit. It has basically a current limiting function. When the current is too much. There is a voltage across R3. Then, Q3 get a biased current. It works, the collector and emitter is low voltage. Thus, Q1 and Q2 stop. No current to load.

Leon Spri

Is it possible to change the output current to 1.5 A with small adjustments? And which are they?

Yes, you can use for 1.5A output when using 2A transformer.


If the output current is always dependent on transformer secondary,
then what is the usefulness of the output transistors

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