Analysis of a charge pump power supply with a floating voltage reference

Charge pump circuits can be used to generate floating power supplies for the high side circuitry of half-bridge inverters. Because of its small input to output voltage drop, the charge pump circuit supports a wide range of supply voltages and is ideal for powering high side circuitry with low voltage requirements. A model for the operation of the charge pump is derived, which offers an improvement over previous models by accounting for the effect of a load current and which includes a variable pump oscillator duty term and current dependent diode models to allow for a more accurate prediction of the charge pump behavior. More importantly, the model also predicts the critical effects of switching transients at the output of the half-bridge on the charge pump. The model has been verified against experiments and shows a good agreement. Using the model, a charge pump circuit was designed for use as the high side power supply for a typical half-bridge inverter.