Method and apparatus for input charge control of a power supply

Abstract

An example method of controlling a power supply to have a constant current output includes receiving an input current sense signal, an input voltage sense signal, and an output voltage sense signal. A control signal is then generated to control switching of a switch of the power supply to regulate an output current of the power supply. The generating of the control signal includes integrating the input current sense signal during a switching period of the control signal to generate an integrated signal representative of a charge taken from an input voltage source of the power supply. Generating the control signal also includes controlling the switching of the switch such that the integrated signal is proportional to a ratio of the output voltage sense signal to the input voltage sense signal.

What is claimed is: 
     
         1 - 12 . (canceled) 
     
     
         13 . A controller for controlling a switch mode power supply having a switch, the controller comprising:
 a constant current control circuit having a first input to be coupled to receive an input current sense signal, a second input to be coupled to receive an input voltage sense signal, and a third input to be coupled to receive an output voltage sense signal and having an output coupled to provide a first control signal to control switching of the switch to regulate an output current of the power supply, the constant current control circuit including:
 an integrator coupled to the first input to receive the input current sense signal, wherein the integrator is coupled to generate a charge signal representative of a total charge received from an input of the power supply during a switching period of the switch by integrating the input current sense signal; 
 an arithmetic operator circuit coupled to generate a product signal that is proportional to the input voltage sense signal multiplied by the charge signal; and 
 a comparator coupled to the third input to receive the output voltage sense signal and coupled to the arithmetic operator circuit to receive the product signal, wherein the comparator is further coupled to compare the output voltage sense signal with the product signal and to determine a logic state of the first control signal in response, thereto. 
   
     
     
         14 . The controller of  claim 13 , further comprising a constant voltage control circuit to provide a second control signal to control switching of the switch to regulate an output voltage of the power supply in response to the output voltage sense signal. 
     
     
         15 . The controller of  claim 14 , further comprising a logic circuit coupled to the constant voltage control circuit to control switching of the switch in response to the second control signal to regulate the output voltage of the power supply when the output current is less than a threshold current and the logic circuit coupled to the constant current control circuit to control switching of the switch in response to the first control signal to regulate the output current when the output voltage is less than a threshold voltage. 
     
     
         16 . The controller of  claim 15 , further comprising an oscillator to provide a maximum duty cycle signal, wherein a first input of the logic circuit is coupled to receive the first control signal, a second input of the logic circuit is coupled to receive the second control signal, and a third input of the logic circuit is coupled to receive the maximum duty cycle signal. 
     
     
         17 . The controller of  claim 15 , wherein the output voltage is regulated to the threshold voltage when regulating the output voltage and wherein the output current is regulated to the threshold current when regulating the output current. 
     
     
         18 . A controller for controlling a switch of a power supply, the controller comprising:
 a first input to be coupled to receive an input current sense signal, a second input to be coupled to receive an input voltage sense signal, and a third input to be coupled to receive an output voltage sense signal;   an output to provide a control signal to control switching of the switch to regulate an output current of the power supply;   an integrator coupled to the first input to receive the input current sense signal, wherein the integrator is coupled to generate a charge signal representative of a total charge received from an input of the power supply during a switching period of the switch by integrating the input current sense signal;   an arithmetic operator circuit coupled to generate a reference signal that is proportional to a ratio of the output voltage sense signal to the input voltage sense signal; and   a comparator coupled to the integrator and the arithmetic operator circuit to compare the charge signal with the reference signal and to determine a logic state of the control signal in response, thereto.   
     
     
         19 . The controller of  claim 18 , wherein the arithmetic operator circuit is coupled to divide the output voltage sense signal by the input voltage sense signal to generate the reference signal. 
     
     
         20 . The controller of  claim 18 , wherein the arithmetic operator circuit includes:
 a first variable current source controlled by the input voltage sense signal to generate a first current;   a first integrator coupled to integrate the first current to generate a voltage ramp signal;   a second variable current source controlled by the output voltage sense signal to generate a second current; and   a second integrator coupled to integrate the second current when the switch is in an OFF state to provide the reference signal, wherein the reference signal is proportional to the ratio of the output voltage sense signal to the input voltage sense signal at a time that the voltage ramp signal reaches a reference voltage.   
     
     
         21 . A power supply, comprising:
 an energy transfer element to be coupled between an input voltage source and an output of the power supply;   a switch coupled to the energy transfer element, wherein the switch switches between an ON state and an OFF state in response to a drive signal; and   a controller coupled to the switch to control switching of the switch to regulate an output current of the power supply, wherein the controller includes:
 a first input to be coupled to receive an input current sense signal, a second input to be coupled to receive an input voltage sense signal, and a third input to be coupled to receive an output voltage sense signal; 
 a constant current control circuit coupled to generate a first control signal in response to the input current sense signal, to the input voltage sense signal, and to the output voltage sense signal, wherein the constant current control circuit includes:
 an integrator coupled to the first input to receive the input current sense signal, wherein the integrator is coupled to generate a charge signal representative of a total charge received from an input of the power supply during a switching period of the switch by integrating the input current sense signal; 
 an arithmetic operator circuit coupled to generate a product signal that is proportional to the input voltage sense signal multiplied by the charge signal; and 
 a comparator coupled to the third input to receive the output voltage sense signal and to the arithmetic operator circuit to receive the product signal, wherein the comparator is further coupled to compare the output voltage sense signal with the product signal and to determine a logic state of the first control signal in response, thereto; and 
 
 a logic circuit coupled to generate the drive signal in response to the first control signal. 
   
     
     
         22 . The power supply of  claim 21 , wherein the controller further comprises a constant voltage control circuit to generate a second control signal in response to the output voltage sense signal, the second control signal controlling switching of the switch to regulate an output voltage of the power supply. 
     
     
         23 . The power supply of  claim 22 , wherein the logic circuit is coupled to receive the second control signal to control switching of the switch to regulate the output voltage of the power supply when the output current is less than a threshold current and wherein the logic circuit is coupled to receive the first control signal to control switching of the switch to regulate the output current of the power supply when the output voltage is less than a threshold voltage. 
     
     
         24 . The power supply of  claim 23 , wherein the output voltage is regulated to the threshold voltage when regulating the output voltage and wherein the output current is regulated to the threshold current when regulating the output current.