Control circuits and methods for switching mode power supplies

摘要

A switching mode power supply (SMPS) includes a transformer having a primary winding, a secondary winding for providing an output voltage, and an auxiliary winding. The SMPS also includes a power switch coupled to the primary winding. A first control circuit is coupled to the secondary winding, and is configured to provide a first electrical signal to the secondary winding when the output voltage of the SMPS is less than a reference voltage during a discontinuous time, whereupon a second electrical signal is induced in the auxiliary winding. A second control circuit is coupled to the auxiliary winding and the power switch. The second control circuit is configured to regulate the output of the SMPS by controlling the power switch in response to a feedback voltage signal from the auxiliary winding, and is further configured to turn on the power switch in response to the second electrical signal.

主权项

1. A switching mode power supply (SMPS), comprising:
a transformer having:
a primary winding for coupling to an input power source; anda secondary winding for providing an output voltage of the SMPS; andan auxiliary winding; a power switch coupled to the primary winding; a first control circuit coupled to the secondary winding, the first control circuit being configured to provide a first electrical signal to the secondary winding when the output voltage of the SMPS is less than a reference voltage during a discontinuous time, whereupon a second electrical signal is induced on the auxiliary winding; and a second control circuit coupled to the auxiliary winding and the power switch, the second control circuit being configured to regulate the output of the SMPS by controlling the power switch in response to a feedback voltage signal from the auxiliary winding, the second control circuit being further configured to turn on the power switch during the discontinuous time in response to thea second electrical signal when the output of the SMPS is less than the reference voltage; wherein the first electrical signal causes a ringing voltage waveform in the secondary winding after a damping ringing waveform in the secondary winding that follows a secondary current flow induced by a primary current.