Method and apparatus for offline switch mode power supply with dithered switching frequency

摘要

A circuit for use in a switched mode power supply comprising includes an integrated circuit, a transformer, a capacitor, a low voltage circuit and a current limiting resistor. The IC jitters the switching frequency of the switch based on a bias voltage of the integrated circuit. The IC also includes a current source configured to supply current for operation of the switching regulator when insufficient current is available from the bias input pin. The transformer includes primary, secondary and auxiliary windings. The primary winding receives a rectified line voltage and is coupled to the switch. The capacitor is coupled between the bias input pin and ground. The low voltage circuit is coupled to the auxiliary winding, and provides current to the bias input pin. The current limiting resistor limits current produced by the low voltage circuit to less than that required for operation of the IC.

主权项

1. A circuit for use in a switched mode power supply comprising:
a switch; an integrated circuit including a switching signal generator operably coupled to the switch, the integrated circuit configured to jitter the frequency of the switch based on a voltage available at a bias voltage pin of the integrated circuit, the integrated circuit further comprising a current source coupled between a first terminal of the switch and a bias input pin, the current source configured to supply current for operation of the switching regulator when insufficient current is received through the bias input pin; a transformer comprising a primary winding, a secondary winding and an auxiliary winding, the primary winding operably coupled to receive a rectified line voltage, the primary winding further operably coupled to the first terminal of the switch; a capacitor coupled between the bias input pin and ground; a low voltage circuit operably coupled to the auxiliary winding, the low voltage circuit configured to provide voltage to the bias input pin; a current limiting resistor coupled between the low voltage circuit and the bias input pin, the current limiting resistor configured to limit current produced by the low voltage circuit to less than that required for operation of the integrated circuit.