The bias voltage is supplied by a bias winding on the inductor. Select the turns ratio so that sufficient bias voltage can be achieved at low AC line voltage. The bias capacitor must be large enough to maintain sufficient voltage with AC line variations. Connect a 0.1-μF bypass capacitor between the VCC pin and the GND pin as close to the integrated circuit as possible. For wide line variations, a resistor, RB, is necessary to permit clamping action. The bias voltage should also be clamped with an external zener diode to a maximum of 18 V.
The zero current detection activates when the ZCD voltage falls below 1.4 V. The bias winding can provide the necessary voltage. This pin has a clamp at approximately 5 V. Add a current limiting resistor, RZC, to keep the maximum current below 1 mA.