Field of the Invention
The present invention relates to a circuit configuration for protecting a power MOSFET.
Circuit configurations for protecting power MOSFETs against overvoltage have long been known and are shown, for instance, in the Siemens Datenbuch [Siemens Databook] "Smart-SIPMOS", 1994/95, pages 2-7, FIG. 4. An overvoltage protection circuit configuration disclosed therein includes a Zener diode ZD2 and a diode D1.
A MOSFET semiconductor component with a voltage spike protection element which is also known from German Published, Non-Prosecuted Patent Application DE 41 22 347 A1, includes a transistor element with a gate electrode, a source electrode, and a drain electrode. In it, a Zener diode with a cathode electrode and an anode electrode is coupled to the drain electrode of the transistor element. A horizontal MOSFET element is also presented that has a gate electrode and a drain electrode. The drain electrode is coupled to the anode electrode of the Zener diode, and the source electrode of the MOSFET element is coupled to the gate electrode of the transistor element. A back-gate electrode which is also proposed therein is coupled to the source electrode of the transistor element.
The wiring of the MOSFET referred to at the outset may also be achieved by using an MOS diode which is realized by an MOS transistor having a gate terminal and a drain terminal that are short-circuited, instead of using the diode D1. FIG. 2 shows one such circuit, which is described in more detail below. In particular, such a protective circuit configuration is used in high-side switches with a charge pump. The MOS diode then takes on the task of blocking the high gate voltage from the supply in the normal operating state. In the event of overvoltage, that MOS diode is operated in the conducting direction, but the on-state voltage can assume undesirably high values under some circumstances.