Negative voltage generator circuit

For sensor circuits or op amp circuits, positive and negative dual power supplies are often required. However, for equipment such as vehicles that only have a single power supply, it is necessary to obtain negative power from a single positive power supply. There are many ways to do this, but using a commercially available DC-DC converter is more convenient.

However, for situations where only a negative power supply is needed to provide a small current, a charge pump circuit composed of timing IC555 can be used. Although the output voltage varies with the output current, the circuit is simple and low cost.

The circuit is shown in Figure 1. Theoretically, it can provide a negative voltage output equal to the 555 supply voltage. But in fact, the negative voltage output value is slightly lower than the absolute value of the power supply voltage because the diodes D1 and D2 have a forward voltage drop VF of about 0.6V.