Dual-rail Variable DC Power Supply

Simple add-on for a single-rail supply

±2.5V to ±15V output

Circuit diagram:

Dual-rail Variable DC Power Supply


R1,R2____________4K7 1/2W 1% or 2% Metal Oxide Resistors

C1,C4,C5_______100nF  63V Polyester Capacitors
C2,C3__________220µF  25V Electrolytic Capacitors

Q1____________BD437   45V 4A NPN Transistor
Q2____________BD438   45V 4A PNP Transistor

IC1___________LM358   Low Power Dual Op-amp

Input and output connecting terminals etc.


This design was conceived as an add-on for the Variable DC Power Supply, a very successful circuit posted to this website in the year 2000.
This simple unit provides a dual-rail variable output ranging from ±2.5V to ±15Vdc with precise tracking of the positive and negative output voltages, still retaining the current limiting and short-proof capabilities of the "master" circuit.
As the purpose of such a dual-rail design is to supply experimental or under-repair circuits, the maximum current output delivered was deliberately kept to about 500 - 600mA per rail, thus avoiding the use of expensive power transistors and complex circuitry.