Regulated voltage dual power supply circuit: +Vcc, –Vcc & Ground

Dual power supplies or dual power supply units are the most common equipment for an electronics hobbyist. It gives positive polarity, negative polarity and ground potential. Some Op Amps need dual power source that is +Vcc and –Vcc (Positive and Negative polarity). This article explains how to construct simple regulated dual power supply circuit with low cost components. It uses two types of voltage regulator ICs 7805 and 7905. 7805 is a positive voltage regulator where as 7905 is a negative voltage regulator IC. This dual voltage power supply definitely helps to develop your own DIY circuits.

Recommended: Dual power supply from single battery source

Circuit diagram

Components required

1. Step down center tapped transformer 6V-0-6V secondary
2. Bridge rectifier (1n4007 Diodes x 4) 
3. Capacitors (470µF, 16V or above x 2) 
4. 7805 Voltage regulator 
5. 7905 Voltage regulator

Working

• Firstly the step down transformer step downs the line voltage to 6V AC. 

• The low voltage AC is fed to a bridge rectifier circuit which converts the alternating current (AC) to direct current (DC) with ripples. 

• We get complimentary waves from the two points A, B marked in the circuit. The waveforms are shown below.

At point A

At point B

• The positive wave’s ripples (pulsating nature) is removed by the capacitor C1, Similarly C2 removes the ripples from the –ve wave.

• Hence we obtain +ve and –ve DC voltages at the points C, D respectively.

At the point C

At the point D

• These voltages are unregulated supply that is the DC voltage varies with respect to line voltage fluctuations.

• The unregulated voltages are regulated by two voltage regulator ICs 7805 and 7905. 

• 7805 is a positive voltage regulator and 7905 is a negative voltage regulator. The pin outs of voltage regulator ICs are also given.

Pin outs of 7805 and 7905 voltage regulators

7805 Voltage regulator IC Pin Out
7905 Voltage regulator IC Pin Out

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