Dual Supply From Single Battery Source

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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:

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.

The output from voltage regulator IC2 is -9V. Assemble the circuit on a general-purpose PCB
and enclose in a suitable cabinet. Fix the 9V battery inside the
cabinet. At the front panel, connect three terminals for outputs. EFY note. This power supply can be used only for low-power applications.