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# Dual Supply From Single Battery Source(LM7909)

2016-05-11 04:44
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This article describes the Dual Supply From Single Battery Source (LM7909). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: LM7909.

Dual-voltage power supply is required especially for powering the op-amps and some of the instrumentation amplifiers. A few low-power audio pre-amplifiers also use dual-voltage supply. This circuit provides both 9V as well as -9V supply from a single 9V battery. It consists of timer IC NE555 (IC1), negative-voltage regulator IC 7909 (IC2) and a few discrete components.

Timer IC NE555 is configured as a free-running oscillator. It produces around 100kHz frequency. An audio system would not pick up this frequency as it is above the audible range. Therefore a Villard cascade voltage multiplier is used as the voltage booster. The boosted voltage is made ripple-free and regulated to -9V by negative-voltage regulator LM7909.

Circuit diagram:

#### Figure 1

The frequency of the squarewave generator depends on the values of C1, R1 and R2. The frequency of the signal may slightly change with the temperature variation but the change in frequency does not affect the output voltage of the circuit. Capacitors C3, C4, C5 and C6 and diodes D1, D2, D3 and D4 form the Villard cascade voltage multiplier. The output voltage from the Villard cascade voltage multiplier is fed to linear negative-voltage regulator IC2 to eliminate ripples and get accurate -9V DC. Capacitors C7 and C8 provide additional noise-filtering.