Isolation of secondary transformer winding current during auxiliary power supply generation

An apparatus comprising:

• a flyback type switching power converter, wherein the switching power converter includes a transformer having a primary-winding, a secondary-winding, and an auxiliary-winding;
• a first switch coupled to the primary-winding;
• an auxiliary power supply that includes auxiliary power supply control circuitry coupled to the auxiliary-winding;
• and
• a controller coupled to the first switch configured to provide a control signal and configured to (i) control the first switch and current in the primary winding and (ii) control the auxiliary power supply circuitry to isolate a transfer of energy from the primary-winding to the secondary-winding from a transfer of energy from the primary-winding to the auxiliary-winding,
• wherein the auxiliary power supply having the auxiliary-winding provides auxiliary power to the controller that provides the control signal to control the transferring of energy from the primary-winding, and the secondary-winding delivers energy for a load of the switching power converter, and
• a capacitor coupled to the controller and to a Zener diode, and a supply voltage node for the controller coupled to the Zener diode, wherein the capacitor and Zener diode are coupled to a current control node of the second switch.