Power Supply Control Circuit and method for sensing voltage in the power supply control circuit

Abstract

The present invention discloses 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 supplying an output signal to the switch control circuit according to voltage signals obtained from two sides of the primary winding, wherein the sensing circuit includes a setting circuit for deciding the output voltage according to a reference signal. The present invention also relates to a voltage sensing method in the power supply control circuit.

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, wherein the sensing circuit includes a setting circuit for providing the setting current signal to decide the output voltage according to a reference signal such that the output voltage is settable by the setting current signal in correspondence to a turn ratio of the secondary winding to the primary winding, the setting circuit providing the setting current signal irrespective of the voltage signals obtained from two sides of the primary winding.   
     
     
         2 . (canceled) 
     
     
         3 . The power supply control circuit of  claim 1 , wherein the sensing circuit comprises a current comparator which generates the output signal by comparing the setting current signal and a difference between the first and the second current signals. 
     
     
         4 . The power supply control circuit of  claim 1 , wherein the sensing circuit comprises a current comparator, which generates the output signal by comparing the second current signal and a sum of the first current signal and the setting current signal. 
     
     
         5 . (canceled) 
     
     
         6 . The power supply control circuit of  claim 1 , wherein the setting circuit comprises:
 a current follower circuit generating the setting current signal according to a reference signal; and   a current mirror duplicating the setting current signal and outputting the duplicated setting current signal.   
     
     
         7 . The power supply control circuit of  claim 1 , wherein the reference signal is determined by a resistor. 
     
     
         8 . The power supply control circuit of  claim 1 , wherein the sensing circuit further comprises a noise masking circuit for masking a noise generated when the power switch is switching. 
     
     
         9 . A method for sensing voltage in the power supply control circuit, comprising the steps of:
 providing a power supply, 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;   providing a power switch electrically connecting to the primary winding;   generating a first and a second current signals (Ia and Ib) according to voltage signals (Vin and Vsw) obtained from two sides of the primary winding;   generating a setting current signal irrespective of the first and second current signals;   controlling the power switch according to the first, the second, and the setting current signals; and   deciding the output voltage according to the setting current signal such that the output voltage is settable by the setting current signal in correspondence to a turn ratio of the secondary winding to the primary winding.   
     
     
         10 . The method of  claim 9 , wherein the step of generating the first and the second current signals according to the voltage signals obtained from two sides of the primary winding comprises: converting the voltage signals to current signals. 
     
     
         11 . The method of  claim 10 , wherein the step of controlling the power switch comprises:
 comparing the second current signal and a sum of the first current signal and the setting current signal; and   controlling the power switch according to the comparison.   
     
     
         12 . The method of  claim 10 , wherein the step of controlling the power switch comprises:
 comparing the setting current signal and a difference between the first current signal and the second current signal; and   controlling the power switch according to the comparison.   
     
     
         13 . (canceled) 
     
     
         14 . The method of  claim 9 , wherein the setting current signal is determined by a resistor 
     
     
         15 . The method of  claim 14 , wherein the step of generating the setting current signal comprises:
 receiving a reference voltage, and   generating the setting current signal according to the resistance of the resistor and the reference voltage.   
     
     
         16 . The method of claim  139 , further comprising the step of: masking a noise generated when the power switch is switching.