Patent ID: 7952898

Claim:
A control circuit for use in a power converter, the control circuit comprising: a logic circuit to be coupled to turn on and turn off a switch of the power converter to regulate an output of the power converter; a first controlled current source coupled to receive a first signal representative of an input voltage of the power converter and to produce a first current that is proportional to the input voltage; a second controlled current source coupled to receive a second signal representative of a reset voltage of a transformer included in the power converter and to produce a second current that is proportional to the reset voltage; and an integrating capacitor coupled to be charged with the first current while the switch is on and to be discharged with the second current when the switch is off, wherein a voltage on the integrating capacitor is representative of a magnetic flux of the transformer, and wherein the logic circuit is adapted to turn off the switch when the voltage on the integrating capacitor is greater than or equal to a first threshold voltage, and to allow the switch to turn on and off in accordance with a pulse width modulation signal after a delay time that begins when the integrating capacitor discharges to a second threshold voltage.