VOLTAGE INVERTER

A useful circuit if you need a split or negative voltage supply, for example for op-amps, but only want to use a single battery.

 CIRCUIT DESCRIPTION

The heart of the circuit is the square-wave astable formed by the 555 IC. In the diagram shown it runs at a frequency of about 75Hz. When the output is high, C2 charges to about 8.3v through D1. When the output goes low, the positive plate is at 0v and the negative plate is 8.3 volts less thus producing -8.3volts and charges C3 to about 7.4 volts through D2. Note each time voltage transfers, 0.7 volts is lost due to the forward drop in the diodes. This leaves an negative voltage of 7.4 volts across C3. Any voltage supply up to about 16volts can be used with -Vout = -Vsupply-1.4v POINTS TO NOTE

Due to the pumping action it takes about 700ms to reach full output voltage. This can be seen right. To reduce this, decrease C3, but this will cause more ripple on the output. The current is limited to about 20mA. With the values shown the current available is as follows: Current Vout no load 7.4 v 5mA 7v 10mA 6v 20mA 4.2v	Blue Trace: Vpump Red Trace: Vout
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