Primary side sampled feedback control in power converters

摘要

A primary-side sampled feedback system includes a sample acquisition phase during which the voltage across the clamp capacitor is sensed as a measure of the primary-reflect output voltage. One end of the clamp capacitor is ground-referenced during the sample acquisition phase. The sample circuitry, which may include a transformer-coupled input for receiving the gate drive of the secondary switch, may use primary side, secondary-side, or primary and secondary side signals to generate the sample acquisition control pulse and clamp switch drive signal. The sample acquisition control pulse occurs when the secondary current reaches its minimum or zero.

主权项

1. A controller for use in a power converter that delivers power from an input source at an input voltage for delivery to a load at an output voltage, the power converter comprising,
a transformer having a primary winding and a secondary winding, secondary circuit elements connected to the secondary winding to deliver power to the load at the output voltage, clamp circuitry connected to the transformer, the clamp circuitry comprising a clamp switch and a clamp capacitor, one or more primary switches connected to the primary winding, wherein the controller is configured to operate the clamp switch and the one or more primary switches in a series of converter operating cycles, each converter operating cycle comprising the following phases:
(a) an energy storage phase during which energy is transferred from the input source to the primary winding of the transformer,(b) an energy transfer phase during which energy is transferred from the secondary winding of the transformer to the load and characterized by connecting the clamp capacitor to the transformer, and(c) a sample acquisition phase during which a voltage across the clamp capacitor is sensed and characterized by the voltage across the clamp capacitor during the sample-acquisition phase being substantially a function of the primary-reflected output voltage, and wherein the controller is configured to control the output voltage as a function of the sensed voltage.