Dual-rail Variable DC Power Supply

Description

This design was conceived as an add-on for the Variable DC Power Supply, a very successful circuit posted to this website. 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.

Circuit Diagram:

Parts:

R1 = 4.7K-1/2W
R1 = 4.7K-1/2W
C1 = 100nF-63V
C2 = 220µF-25V
C3 = 220µF-25V
C4 = 100nF-63V
C5 = 100nF-63V
Q1 = BD437
Q2 = BD438
IC1 = LM358

Notes:

The circuit can be placed into the existing Variable DC Power Supply metal cabinet.
Q1 and Q2 must be mounted on heatsinks. Usually, bolting them to the metal case (through insulating washers etc.) proved effective.
The full ±15V output can be achieved only if the secondary winding of the supply Transformer used in the Variable DC Power Supply is rated at 48V minimum (center tapped).
When using this circuit, please set the Current-limit control (P1) of the Variable DC Power Supply to any value comprised in the 50mA - 1A range but not higher.
The second Op-amp (IC1B) contained in the LM358 chip was not used, but its input pins were tied to the negative supply and the output was left open.

circuit from http://www.redcircuits.com