Patent ID: 6392906
Filing Date: 2002-05-21
Classification: H02M,H04N,Y02B

Abstract:
A pwm controller, comprising:a start-up current source that supplies current to a power supply node during a first operating phase and is turned off during a third operating phase; a driver circuit which is turned off during the first operating phase, enabled for drawing current from the power supply node during a second operating phase and turned off during the third operating phase; a supply detector for detecting a supply voltage on the power supply node to initiate the third operating phase when the supply voltage falls below a first undervoltage level and terminate the third operating phase when the supply voltage falls below a second undervoltage level; and a phase duration controller for controlling the duration of the third operating phase wherein the phase duration controller alters the first and second undervoltage levels and the rate at which the voltage at the power supply node falls from the first to the second undervoltage level.