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Wednesday, January 2, 2008

Dual Polarity Power Supply

This dual polarity power supply is easy to build, requires few parts, and is adjustable from 0-15 volts. It is great for powering op amp circuits, as well as other circuits that require a dual supply voltage.

Schematic

Parts

Part

Total Qty.

Description

Substitutions

C1, C2

2

2200uF 35V Electrolytic Capacitor


C3, C4, C5, C7

4

1uF 35V Electrolytic Capacitor


C6, C8

2

100uF 35V Electrolytic Capacitor


R1, R4

2

5K Pot


R2, R3

2

240 Ohm 1/4 W Resistor


BR1

1

2A 30V Bridge Rectifier


U1

1

LM317 Adjustable Positive Regulator


U2

1

LM337 Adjustable Negative Regulator


T1

1

30V Center Tapped 2 Amp Transformer


S1

1

SPST 2 Amp Switch


MISC

1

Heatsinks For U1 And U2, Line Cord, Case, Knobs For Pots, Wire


Notes

1. Since this project operates from 120 (or 220, or 240, etc.) volts AC, it MUST be built inside a case.

2. U1 and U2 get quite hot and will require heatsinks. A fan is usually not needed.

3. You can, of course, add a volt and amp meter.

4. U1 and U2 can only go down to a minimum of +-1.2V. If you need to go lower, you can add two 1N4003 diodes in series with the output of the regulator. The diodes drop about 0.6V each, which will allow the supply to go to 0. Note that this will also decrease your maximum output voltage by 1.2V.

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