A system includes a transformer having an auxiliary coil to provide a flyback voltage to a primary side of an alternating current to direct current (AC-DC) converter. A primary side controller includes an auxiliary pin coupled to the transformer and to an external capacitor, the auxiliary pin to receive the flyback voltage after startup. a junction gate field-effect transistor (JFET) coupled to a supply voltage. A first FET is coupled in series between the JFET and the auxiliary pin, the JFET to charge the external capacitor from the supply voltage during startup. One or more depletion region diodes are coupled to a gate of the first FET, the one or more depletion region diodes to bias a voltage of the gate of the first FET to a specific voltage.