Friday, February 20, 2009

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.



Total Qty.
C1, C222200uF 35V Electrolytic Capacitor
C3, C4, C5, C741uF 35V Electrolytic Capacitor
C6, C82100uF 35V Electrolytic Capacitor
R1, R425K Pot
R2, R32240 Ohm 1/4 W Resistor
BR112A 30V Bridge Rectifier
U11LM317 Adjustable Positive Regulator
U21LM337 Adjustable Negative Regulator
T1130V Center Tapped 2 Amp Transformer
S11SPST 2 Amp Switch
MISC1Heatsinks For U1 And U2, Line Cord, Case, Knobs For Pots, Wire


  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. (Thanks to Steve Horvath for the suggestion).



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