In this electronics project, I will demonstrate how to make a DC to DC variable power supply using the well-known integrated circuit LM317, along with a current booster NPN power transistor.
This circuit setup will enable us to adjust the output voltage up to 30V and the output current up to 5A. It can be used as a bench power supply equipment during circuit making or testing.
Let's make it!
Components for Variable Power Supply
The following components are required to make this power supply circuit:
| Name | Value | Qty. |
|---|---|---|
| U1: Adjustable Voltage Regulator | IC LM317 | 1 |
| Q1: NPN Power Transistor | 2N3055 | 1 |
| Q2: NPN Transistor | BD139 | 1 |
| R1: Resistor | 1kΩ, 1/4W | 1 |
| R2: Resistor | 220Ω, 1/4W | 1 |
| R3: Resistor | 1Ω, 5W | 1 |
| POT1: Variable Resistor | 5kΩ | 1 |
| POT2: Variable Resistor | 10kΩ | 1 |
| D1: LED | 5MM | 1 |
| D2: Diode | 1N4007 | 1 |
| C1: Flim Capacitor | 0.1uF | 1 |
| J1, J2: Connector | 2-Pin Screw Terminal Block | 2 |
| Aluminium Heat Sink | 40MM x 55MM (H x W) | 1 |
| Veroboard | 60MM x 30MM (W x L) | 1 |
| Heat Sink Tube | 3MM | 1 |
| Connecting Wires | - | - |
| Soldering Kit | - | 1 |
Variable Power Supply Circuit Diagram
Schematic of variable power supply circuit with adjustable dc 1-30v 0-5a is shown below. To increase the current handling capacity to 10A of this circuit, you needed to parallelly connect the similar value of two power transistors (Q1) and two current limit resistors (R3).
After Soldering Variable Power Supply Circuit
I arranged the components and soldered the variable power supply circuit onto a Veroboard following the schematic. Here, you can see the complete circuit board after the soldering.
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Testing & Demo - 1-30V, 0-5A Variable Power Supply
Usually, this circuit can be adjusted from 0 to 5A current, but it can handle up to 7A with the proper aluminum heat sink and cooling fan for temperature control.
To test the circuit, I used a 24V 3A DC power source and adjusted the regulated output voltage to 12V using Voltage controlling potentiometer (POT1).
Next, I connected a 12V 10W halogen light bulb as a load and adjusted the current to a safe level using Current controlling potentiometer (POT2). Here, you can see the testing operation of the variable power supply.
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