Patent ID: 7391201

Claim:
A method to achieve a regulated analog transistor switch providing a constant output voltage not exceeding a defined voltage limit, wherein a supply voltage could be much higher than this defined output voltage limit and wherein the ON-resistance of the transistor switch can be reduced to a minimum is comprising: providing a supply voltage being smaller than the maximum extended drain voltage of said transistor switch, said transistor switch, a voltage divider between said output voltage and ground, a differential amplifying means having its output connected to the gate of said transistor switch, a reference voltage being lower than said supply voltage, and a resistive means connected between said supply voltage and the gate of said transistor switch; biasing of said differential amplifying means with said supply voltage; amplifying the difference between the midpoint voltage of said voltage divider and said reference voltage and using the amplified difference to control the gate of said transistor switch; minimizing the ON-resistance of said high voltage transistor by applying a constant maximum allowed gate-source voltage to said transistor switch in case said supply voltage is smaller or equal than said defined output voltage; and clipping of the output voltage by adjusting said reference voltage and said voltage divider.