Transformerless capacitive coupling of gate signals for series operation of power MOS devices

A reliable configuration for triggering a series string of power MOS devices without the use of transformer coupling is presented. A capacitor is inserted between the gate and ground of each MOSFET, except for the bottom MOSFET in the stack. Using a single input voltage signal to trigger the bottom MOSFET, a voltage division across the network of device capacitance and inserted capacitances triggers the entire series stack reliably. Design formulae are presented and simple circuit protection is discussed. Simulation shows reliable operation and experimental verification is presented. Application of the method is applied to series IGBTs