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.
