Power chip set for a switching mode power supply having a device for providing a drive signal to a control unit upon startup

摘要

A power chip set for a switching mode power supply includes a high voltage chip and a control unit chip. The high voltage chip contains a switching power metal-oxide-semiconductor (MOS) transistor being turned on/off under control of an output signal from the control unit, and a junction field effect transistor (JFET) coupled between a drain of the switching power MOS transistor and a power terminal of the control unit to serve as a start up element for driving the control unit during initiation, in which the JFET has a negative threshold voltage and the absolute value thereof is equal to the voltage for driving the control unit. The JFET structure in the high voltage chip further includes a Zener diode for over voltage protection of the control unit. The high voltage chip further contains a current-sense power MOS transistor coupled with the drain of the switching power MOS transistor for detecting a drain current of the switching power MOS transistor. The chip set can be packaged into a power module.