This Universal Power Supply can provide fixed +12V and –12V DC outputs along with an adjustable output ranging from approximately 1.2V to 22V DC, making it suitable for testing, repairing, and powering a wide variety of electronic circuits and modules.
The circuit operates from a 230V AC mains supply through a centre-tapped 15V-0-15V transformer. The transformer steps down the high AC voltage to a safer low-voltage AC level. A bridge rectifier made using four diodes converts the AC voltage into pulsating DC, while large electrolytic capacitors smooth the ripple and provide stable DC filtering.
For fixed outputs, IC LM7812 generates a regulated +12V supply and IC LM7912 produces a regulated –12V output. These outputs are useful for operational amplifier circuits, analog projects, audio applications, and dual-supply systems. The adjustable section is built around the LM338 high-current adjustable voltage regulator. By adjusting preset VR1, the output voltage can be varied smoothly from around 1.2V up to 22V DC. Resistors and capacitors around the regulator improve voltage stability and transient response.
A DC voltmeter module is also included to continuously monitor the adjustable output voltage, making the power supply more user-friendly and convenient during experimentation. Protection diode D1 safeguards the regulator from reverse voltage conditions.
