Variable voltage power supply is essential for any electronic hobbyist to begin their electronics lessons. For different applications, you may need different voltages. So it becomes impossible to use multiple fixed power supplies all the time.
Also, this variable power supply circuit ensures the protection of other circuit parts from voltage fluctuations. So in this article, we will teach you how to build a variable power supply on your own. Why buy when you can make one of your own easily using very few components?
Assemble this circuit on a PCB (Printed Circuit Board) and start your electronics projects. You can connect the output to a multimeter for displaying the voltage.
How to Make a Variable Power Supply?
This supply unit uses an LM3 17 voltage regulator IC. The rectified output from the full wave bridge rectifier is fed to an LM317 regulator IC. By changing the value of the potentiometer used in this circuit, the output voltage can be controlled easily.
Note: For safety, use this circuit to get a maximum of 30 volts.
Variable DC Power Supply Schematic
- LM317 Regulator IC
- Step down transformer (230V to 30V)
- Resistor (1KΩ; 220Ω)
- Potentiometer (5KΩ)
- Capacitor (1µF; 35V)
- Capacitor (2200µF, 0.1µF)
- Bridge rectifier
- 1N4007 Diode
Working of Adjustable Power Supply Circuit
- The first section is a full wave diode bridge rectifier which we have already posted previously.
- LM 317 provides an output voltage that can be varied from 1.2V to 35V maximum by adjusting the potentiometer.
- Another striking thing is that lm317 has inbuilt current limiting and thermal shutdown features.
- A reference voltage of 1.25 V is maintained at the time of operation across the resistor R2.
- The 1uF capacitor across the output helps in getting a better transient response.
- Diode D1 is a protection diode that prevents the C3 from discharging into the regulator IC caused by a short circuit of input to the ground.