Split supply: ± rails for op-amps
Two secondary windings in series with their junction as ground (a centre tap) feed one bridge: its + output is positive and its − output negative with respect to the tap. Two capacitors and a 7805/7905 pair give regulated +5 V and −5 V.
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How it works
Each half of the secondary peaks at 12·√2 ≈ 17 V; less one diode drop and the ripple, the raw rails sit near ±15 V.
The regulators give +5.00 V and −5.00 V. Note the 7905’s pinout: GND, IN, OUT.
Try it on the bench
- Swap the wires of C− round: an electrolytic in a negative rail goes + to ground.
Parts on the bench
- AC source
- 2 × Transformer
- Bridge rectifier
- 2 × Electrolytic capacitor
- 7805 regulator
- 7905 negative regulator
- 2 × Resistor
In the course
Electronics Technician, module “Power supplies”.