Simple Dual Power Supply Circuit Without Center Tap

The article explains how to make a simple dual power supply circuit without using a center tap transformer rather any ordinary two wire transformer.

This circuit is of interest not merely  because it uses a bell transformer  with a single secondary winding to  provide symmetrical voltages for  low-current applications but also  because the final output voltages  are greater than the normal bell  transformer (220 V/8 V) output. In  fact the final output can be as much  as twice this value.

This multiplication  is achieved using two voltage doublers  each consisting of two diodes and  two capacitors, connected head to  tail.

Each diode/capacitor couple  takes every alternate half cycle of  the sinusoidal voltage such that the  output voltage U is (theoretically)  equal to 2V2 Ueff where Ueff is  the effective output voltage of the  transformer.

A current of 150 . . . 200 mA and  1 V of ripple can be expected using  the capacitor values shown here. ln  order to increase this current without  a similar increase in ripple the values  of the capacitors may be made  greater but C1 must be approximately the same as C2, and C3 about  the same as C4.

To get a stable symmetrical output  of 15 V two voltage regulators, a  7815 and a 7915, should be used.  This enhanced simple dual power supply circuit will then allow any two wire transformer to be used for any small circuits  with operational amplifiers requiring  a symmetrical supply of 14 or 15 V  and a current of 0.1 .. . 0.2 A.


simple dual power supply circuit