Synchronous rectifier controller for a switched mode power supply

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.