Method and system of driving an electrically controlled switch with a snubber capacitor

A method of operating a power converter, comprising:

• charging a snubber capacitor coupled to a secondary winding of a transformer arranged for flyback operation, the charging during a charge mode of a primary winding of the transformer;
• charging a gate of a secondary field effect transistor (FET) with current from the snubber capacitor, the charging of the gate during a discharge mode, and the charging makes the secondary FET fully conductive before a secondary rectifier coupled in series with the secondary FET is forward biased, the discharge mode is contiguous with the charge mode;
• providing current through the secondary rectifier and the secondary FET to a secondary output node of the power converter, the secondary rectifier coupled in series with the secondary FET;
• and
• making the secondary FET non-conductive.

A switching power converter comprising:

• a primary side including:
• a primary winding of a transformer;
• a main switch coupled between the primary winding and a reference voltage on the primary side, the main switch defining a control input;
• a primary-side controller coupled to the control input of the main switch and a voltage feedback circuit, the primary-side controller configured to control the main switch based on a voltage indicative of a low-side voltage output;
• a secondary side including:
• a low-side secondary winding of the transformer coupled to the low-side voltage output;
• a low-side rectifier coupled between the low-side secondary winding and the low-side voltage output, the low-side secondary winding and the low-side rectifier arranged for flyback operation of the low-side secondary winding;
• a high-side secondary winding of the transformer coupled to a high-side voltage output;
• a high-side rectifier defining an anode and a cathode, the anode coupled to the high-side secondary winding;
• a secondary field effect transistor (FET) defining a gate, a source, and a drain, the drain coupled to the cathode of the high-side rectifier, and the source coupled to the high-side voltage output;
• a snubber capacitor having a first lead coupled directly to the anode of the high-side rectifier, and a second lead of the snubber capacitor coupled directly to the gate of the secondary FET;
• a secondary-side controller coupled to the gate of the secondary FET, the source of the secondary FET, and the high-side voltage output, the secondary-side controller configured to sense each discharge mode of the switching power converter, and during each discharge mode control a length of time the secondary FET is conductive based on a voltage of the high-side voltage output.