This is simple 0-20V variable Power supply circuit diagram at a maximum output current of about 1A. Which use common components that easy to buy in any store, and use transistors as main and control the output voltage with a potentiometer. It also is an adjustable power supply for model railways and general projects.
My Friend comes to see me. He brings a lot of electronic PCB. He asks me, what do we do with them? It is a great idea for recycling.
I like to make a DC power supply project. Lets to make a simple 0-20V variable Power supply circuit. He says okay, good idea.
He will apply them with the old power amplifier, about 40 years ago. Though very ancient, some parts still have many uses. We like it.
How it works
In the circuit above, When 220V/120VAC main comes to the circuit, pass through ON/OFF switch-S1 and Fuse-F1.
Then, transformer T1 changes 220VAC to about 24VAC.
After that, The rectifier bridge, D1 through D4, rectifies the AC into pulsating DC.
The capacitor C1 acts as a storage capacitor, it will filter DC to smooth up as the unregulated power supply.
Now we have the 36V DC voltage at C1. Then this flow through to R1 and both Zener diodes ZD1 and ZD2, in series, each Zener is 10V. They are a reference voltage. Using R1 limits current to ZD1 and ZD2 to keep the voltage constant at about 20V.
Next, this voltage comes to the base of Darlington regulator Q1, Q2. Both transistors will increase current up, so there are the voltage constant across R4 or output to load.
Why we add these components:
- Potentiometer VR1, adjust the output voltage from 0V to 20V
- Capacitor C2, the voltage drop across VR1 to be stable up
- Both Capacitors C3, C4, reduce a noise signal (transient noise) in a circuit.
- Diode D5, protect a feedback voltage that may kill other components
He uses all the transistor from it. You can change a transistor number instead Such as TIP41, TIP31, 2SD313, H1061, 2SC1061, MJE3055 and more. But its key feature is at least of 3A, 40V, NPN transistors.
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