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NEGATIVE SUPPLY

A negative supply can be generated with a 555 operating in astable mode. The generated voltage is approximately 3v less than the rail voltage due to pin 3 rising to about 1.7v below rail voltage, plus the loss in the power diode. A small loss is produced by the electrolytic in the diode-pump design, creating an overall loss of approx 3v.

The output current should be kept to below 50mA, otherwise the output voltage will drop further.