555 Negative Voltage Power Supply Circuit
A negative supply can be generated by a “Charge-Pump” circuit created with a 555, diodes and capacitors.
Another advantage of this circuit is that, the negative voltage together with the original positive supply can be used to simulate a dual supply.
This circuit diagram shows how to obtain a negative voltage from a positive voltage supply.
The 555 is connected as an astable multivibrator operating at around 1KHz. During the timer output at pin 3 goes positive, the series C3 capacitor charges through the diode D1. When the output switches to ground, the C3 cap discharges through the D2 and charges the C4 capacitor to a negative voltage. As a result of this the voltage at the junction of the anode of D2 and cathode of C4 will be always negative with respect to the ground.
The output will deliver about 50mA.