Patent ID: 8374001
Filing Date: 2013-02-12
Classification: H02M

Abstract:
1. A power supply control circuit, the power supply providing an output voltage to an output terminal from an input terminal through a transformer having a primary winding and a secondary winding, the power supply control circuit comprising: a power switch electrically connected with the primary winding; a switch control circuit controlling the power switch; and a sensing circuit converting voltage signals (Vin and Vsw) obtained from the two sides of the primary winding to a first and a second current signals (Ia and Ib), and supplies an output signal to the switch control circuit according to the first, the second, and a setting current signal (Iset), wherein the sensing circuit includes a setting circuit for providing the setting current signal to decide the output voltage such that the output voltage is settable by the setting current signal in correspondence to a turn ratio (N) of the secondary winding to the primary winding, wherein Ia=gm*Vin and Ib=gm*Vsw, in which Vin and Vsw are the voltage signals obtained from the two sides of the primary winding; Ia and Ib are the first and second current signals converted from the voltage signals Vin and Vsw, respectively; and gm is a conversion ratio by which the sensing circuit converts the voltage signals Vin and Vsw to the first and second current signals Ia and Ib, respectively; and wherein the output voltage and the setting current signal has the following relationship: Vout=(1/gm)*N*Iset, wherein Vout is the output voltage; N is the turn ratio of the secondary winding to the primary winding is N; and Iset is the setting current signal.