A novel tri-state driver to improve the switching performance in automotive converter

A novel low cost tri-state driver is presented to reduce the overvoltage of the synchronous MOSFET in an automotive dc-dc converter. A third high-impedance state allows the MOSFET to be driven in the linear mode for a few nano seconds. The reverse recovery current of the body diode is therefore diverted and does not charge the junction capacitance. This leads to a reduced voltage stress of the MOSFET and an improved EMI behavior of the converter. The value of the overvoltage can be controlled with a simple voltage source in the gate circuit. An analysis has been done to predict the overvoltage dependent on the voltage of this voltage source. Prototypes with different MOSFETs were built and tested to prove theoretical predictions. The additional power losses caused by the operation in the linear mode are small in this application.