Patent ID: 8130517

Claim:
A power converter, comprising: a transformer having a primary winding; a switch coupled to the transformer to selectively apply an input voltage to the primary winding; a reset circuit coupled to the primary winding to generate a reset circuit voltage from a magnetizing current that leaves the transformer when the switch is off; and a control circuit coupled to the switch, wherein the control circuit includes: a pulse width modulator coupled to generate a pulse width modulation signal in response to a feedback signal; logic circuits coupled to turn the switch on and off to regulate an output of the power converter in response to the pulse width modulation signal; and saturation prevention circuits coupled to the logic circuits to assert a first signal when a first integral value of the input voltage reaches a first threshold value and to assert a second signal after a delay time that begins when a difference between the first integral value and a second integral value of a reset voltage of the transformer falls to a second threshold value, wherein the logic circuits are adapted to turn off the switch when the first signal is asserted, and to allow the switch to turn on and off in accordance with the pulse width modulation signal when the second signal is asserted.