High voltage integrated circuit driver for half-bridge circuit employing a jet to emulate a bootstrap diode

摘要

A half-bridge driver circuit including a lower drive module and a floating upper drive module for driving respective external upper and lower power transistors of a high voltage half bridge is contained in an integrated circuit chip which includes an on-chip bootstrap diode emulator which is turned on in response to a control signal applied to its gate in order to pass current from a power supply to charge an external bootstrap capacitor that powers the upper drive module. The upper drive module is accommodated in an insulated well and the diode emulator includes as its main current carrying element, a JFET transistor formed along the periphery of the well. The JFET transistor is driven into a conducting state at the same time the lower power transistor is driven into a conducting state. The source electrode of the JFET is coupled to the power supply via a diode, such that the voltage at said source electrode cannot rise above a level which is one diode drop below the voltage at said power supply output and control circuitry derives the control control signal in a manner that it is constrained not to rise a level which is three diode drops below the voltage at the power supply output and limits the current that may flow in the gate electrode.