Synchronous rectifier controller for a switched mode power supply

摘要

Consistent with an example embodiment, a synchronous rectifier controller for a switched mode power supply comprises a transformer with a secondary side winding and a synchronous rectifier transistor with a gate, a source and a drain; the source and drain provide a conduction channel coupled to the secondary side winding. The controller comprises an input terminal for receiving an input signal related to a voltage at the drain, an output terminal configured to provide an output signal for setting a logic state of the gate, and circuitry having a first threshold and a second threshold. The circuitry is configured to generate the output signal and determine a time period in accordance in accordance with a comparison between the input signal and the first threshold; and in accordance with a comparison between the input signal and the second threshold, set the first threshold in accordance with the time period.

主权项

1. A synchronous rectifier controller for a switched mode power supply comprising an inductive winding and a synchronous rectifier transistor with a gate, a source and a drain, the source and drain providing a conduction channel coupled to the inductive winding, the synchronous rectifier controller comprising:
an input terminal for receiving an input signal related to a voltage at the drain; an output terminal configured to provide an output signal for setting a logic state of the gate; and circuitry having a first threshold and a second threshold, the circuitry configured to:
generate the output signal in accordance with a comparison between the input signal and the first threshold;determine a time period in accordance with the comparison between the input signal and the first threshold and in accordance with a comparison between the input signal and the second threshold;set the first threshold in accordance with the time period; wherein the circuitry comprises a timing capacitor and is configured, in order to measure the time period, to: initiate supply of a current to the timing capacitor in response to the input signal becoming equal to or crossing the first threshold such that a timing charge is accumulated by the timing capacitor; and cease supply of the current to the timing capacitor in response to the input signal becoming equal to or crossing the second threshold.