Patent ID: 7423856

Claim:
A switching power supply controller comprising: a first input configured to receive a first voltage from a voltage source external to the switching power supply controller; a first portion of the switching power supply controller operably coupled to detect a fault condition; a first circuit of the switching power supply controller configured to operably couple the first circuit to use the first voltage to form a first operating voltage for operating the first circuit responsively to the switching power supply controller detecting the fault condition and operably coupled to assert a control signal responsively to the switching power supply controller detecting the fault condition, the first circuit operably coupled to negate the control signal responsively to the first operating voltage decreasing to a first value and to decouple the first circuit from operating from the first operating voltage responsively to the negated state of the control signal; the first circuit configured to generate a second operating voltage for operating a second portion of the switching power supply controller wherein the second operating voltage is different from the first operating voltage, the first circuit configured to disable the second operating voltage responsively to asserting the control signal; and a PWM control circuit of the switching power supply controller configured to use the second operating voltage to operate the PWM control circuit.