Patent ID: 7535130

Claim:
An integrated circuit controller for a power supply, the controller comprising: a reference terminal; a high voltage terminal adapted to withstand a first maximum voltage relative to the reference terminal; a third terminal adapted to withstand a second maximum voltage relative to the reference terminal, wherein the second maximum voltage is substantially greater than the first maximum voltage; a power switch coupled between the high voltage terminal and the reference terminal, the power switch adapted to switch during a normal mode of operation of the controller; a high voltage buffer circuit coupled to the high voltage terminal to provide an internal voltage representative of a voltage at the high voltage terminal; and low voltage circuitry coupled to the high voltage buffer circuit to monitor the internal voltage, wherein the low voltage circuitry is adapted to set the normal mode of operation of the controller if the internal voltage is above a first threshold voltage, wherein the low voltage circuitry is further adapted to set an alternative mode of operation of the controller if the internal voltage is below a second threshold voltage.