Patent ID: 8542508
Filing Date: 2013-09-24
Classification: H02M

Abstract:
1. A saturation prevention circuit for use in a control circuit that produces a gate signal to turn a switch on and off to regulate an output of power converter in response to a feedback signal, the saturation prevention circuit comprising: a first controlled current source coupled to receive a line voltage sense signal representative of an input voltage that is to be applied to a winding of a transformer included in the power converter, wherein the first controlled current source generates a first current that is directly proportional to the input voltage in response to the line voltage sense signal; a second controlled current source coupled to receive a reset voltage sense signal representative of a reset voltage that is to be applied to the winding of the transformer, wherein the second controlled current source generates a second current that is directly proportional to the reset voltage in response to the reset voltage sense signal; an integrating capacitor to be coupled to the first controlled current source to charge the integrating capacitor with the first current while the input voltage is applied to the winding of the transformer and to be coupled to the second controlled current source to discharge the integrating capacitor with the second current while the reset voltage is applied to the winding; and a first comparator coupled to the integrating capacitor to compare a voltage on the integrating capacitor with a first threshold, wherein the first comparator generates a first signal to immediately turn off the switch when the voltage on the integrating capacitor reaches the first threshold to limit a magnetic flux in the transformer and to prevent saturation of the transformer.