Patent ID: 8611108

Claim:
A control element for use in a power supply, comprising: a high-voltage transistor, including: a drain region of a first conductivity type; a source region of the first conductivity type; a tap region of the first conductivity type; a body region of a second conductivity type, the body region adjoining the source region; a drift region of the first conductivity type extending from the drain region to the body region; a tap drift region of the first conductivity type extending from the drain region to the tap region, wherein the tap region adjoins the tap drift region at an end of the tap drift region opposite the drain region; and an insulated gate disposed such that when the insulated gate is biased a channel is formed proximate to the insulated gate across the body region to form a conduction path between the source region and the drift region; and a control circuit coupled to the insulated gate and to the tap region to control switching of the high-voltage transistor to regulate an output of the power supply, wherein a voltage at the tap region with respect to the source region is substantially constant and less than a voltage at the drain region with respect to the source region in response to the voltage at the drain region exceeding a pinch off voltage.