Patent ID: 8804380

Claim:
A switching mode power supply (SMPS), comprising: a transformer having: a primary winding for coupling to an input power source; a secondary winding for providing an output of the SMPS; and an auxiliary winding; a power transistor coupled to the primary winding; a resistor coupled between the input power source and a control terminal of the power transistor for triggering a primary current flow through the power transistor for providing startup power; a primary side control circuit coupled to the auxiliary winding and the power transistor, the primary side control circuit being configured to regulate the output of the SMPS by controlling the power switch in response to a feedback voltage signal that is representative of the output of the SMPS; and a secondary side control circuit coupled to the secondary winding and being configured to provide a first electrical signal to the secondary winding when an output voltage of the SMPS is less than a first reference voltage, whereupon an awakening signal is induced in the auxiliary winding and causes the primary side control circuit to provide a turn-on signal to the power transistor; wherein the primary side control circuit is configured to be in a standby mode under a no-load condition, in which one or more circuit blocks in the primary side control circuit are turned off, and the primary-side control circuit enters into a normal operating mode when two successive awakening signals are received within a predetermined time period.