I will show you an old circuit that interesting. No ICs, no Zener diode. But it is also steady voltage. This is a simple transistor variable power supply, 0-30v 1A project. Why should we make it?

It is a small circuit, cheap and buys easy. The 2SC1061 and small transistors are a main. It will control current up to 1 A. Also, others a few components. You can adjust the output voltage with VR1.  Thus, It is suitable for learning the basic variable regulator.

The details
The ICs—integrated circuit— is so famous in this electronic age. Because they are small, easy and may be 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 the money.

But if IC circuit. We need to change IC. Perhaps it is expensive or we cannot buy it at the local stores.

In this circuit is the series regulator mode so 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 output voltage as we adjust, 0V to 30V.

‘Keep reading: DC Supply adjustable Voltage 0-20V at 1A’ »

The parts of circuit
0.25W Resistors
R1, R2: 10K
R3, R4: 100 ohms
C1: 1000µF 35V Electrolytic
C2,C3: 100µF 35V Electrolytic
Q1,Q2: BC337, 50V 800mA NPN Transistor
VR1: 10K Potentiometer
Q3: 2SC1061 or TIP41 or H1061 or MJE3055, 50V 2A NPN Transistor
D1-D5: 1N4002, 100V 1A Diode

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

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.

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

‘Keep reading: Simple variable dc power supply 0-30V 2A for beginners ’ »

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