Regulated Dual Power Supply

The objective here is to build a dual power supply that generates regulated +12 volts and -12 volts from AC mains. Such a supply is a very common requirement in all those circuits that use opamps.
Each output in the circuit has a current delivering capability of 250mA .

Full wave rectifier


C1,C2 1000uf ,50V Electrolytic
C3,C4,C7,C8 0.1uf Ceramic Disc
C5,C6 10uf ,50V Electrolytic
D1 & D4 1N4001 or Equivalent
IC-1 7812
IC-2 7912
Transformer T1 15-0-15


The unregulated AC/DC power supply part of the circuit consist of a transformer that steps down the power to 15 volts across a center tapped secondary windings I.e. The two half’s of the secondary winding with opposite polarities , diode D1 to D4 that rectifies the AC providing full wave rectification to produce a positive and negative output, capacitors C1 and C2 provide filtration. C3 to C8 are decoupling capacitors. IC-1 is a fixed output positive three terminal regulator whereas IC-2 is a fixed output negative three terminal regulator.

Other variations of the circuit

The same circuit can be used to produce (+5V,-5V) ,(+9V,-9V),(+15V,-15V),(+18V,-18V) and (+24V,-24V).what you need to do is to use different type nos. for the two regulators’ and a different transformer.

Other Varitaions
Desired Output T-1 IC-1 IC-2
+5V,-5V 7.5-0-7.5 250mA 7805 7905
+9V,-9V 12-0-12 250mA 7809 7909
+15V,-15V 15-0-15 250mA 7815 7915
+18V,-18V 18-0-18 250mA 7818 7918
+24V,-24V 24-0-24 250mA 7824 7924