A negative voltage supply for high-side switches using buck-boost bootstrap circuitry

The unipolar gate driving method provides a low cost and simple solution for inverter system design. However, the unipolar gate driving can cause issues like `parasitic oscillation´ during turn-on of power switches and `unintended parasitic turn-on´ caused by the Miller-effect of power semiconductors. Hence the maximum value of gate resistance has to be limited. To overcome the above mentioned issues, a negative gate voltage can be applied to the switch. Unfortunately the standard method for bootstrapping a positive gate voltage cannot be extended to negative voltages without increasing the complexity. The proposed bootstrap circuit can generate a negative gate voltage with minimal increase of components. For this purpose a buck-boost converter is merged with a standard bootstrap topology which can generate a negative as well as a positive gate voltage for high-side switches without additional power supply.