Method and apparatus for a power supply controller responsive to a feedforward signal

Abstract

An example power converter includes an energy transfer element, a switch, a feedback circuit, a feedforward circuit, and an integrated circuit controller. The integrated circuit controller includes a gain selector circuit and a switch duty cycle controller. The gain selector circuit selects a gain multiplier according to a value of a feedforward signal generated by the feedforward circuit and applies the gain multiplier to the feedforward signal to generate a duty cycle adjust signal. The switch duty cycle controller generates a drive signal to control the switch in response to a feedback signal generated by the feedback circuit. A duty cycle of the drive signal is varied in response to the duty cycle adjust signal such that the duty cycle varies according to a plurality of linear functions over a range of values of the feedforward signal.

What is claimed is: 
     
         1 . A power converter, comprising:
 an energy transfer element to be coupled to receive a direct-current (DC) input voltage;   a switch coupled to the energy transfer element to control a transfer of energy through the energy transfer element;   a feedback circuit coupled to generate a feedback signal that is representative of an output of the power converter;   a feedforward circuit coupled to generate a feedforward signal that is representative of the DC input voltage; and   an integrated circuit controller coupled to generate a drive signal to control switching of the switch to regulate the output of the power converter, wherein the integrated circuit controller includes:
 a gain selector circuit coupled to select a gain multiplier according to a value of the feedforward signal and to apply the gain multiplier to the feedforward signal to generate a duty cycle adjust signal; and 
 a switch duty cycle controller coupled to generate the drive signal in response to the feedback signal, wherein a duty cycle of the drive signal is varied in response to the duty cycle adjust signal such that the duty cycle varies according to a plurality of linear functions over a range of values of the feedforward signal. 
   
     
     
         2 . The power converter of  claim 1 , wherein the feedforward circuit is coupled directly to receive the dc input voltage of the power converter to generate the feedforward signal. 
     
     
         3 . The power converter of  claim 1 , wherein the energy transfer element is a transformer having an input winding, an output winding, and a forward winding, wherein a voltage appearing across the forward winding during an on time of the switch is directly proportional to the dc input voltage and wherein the feedforward circuit is coupled to the forward winding to generate the feedforward signal. 
     
     
         4 . The power converter of  claim 1 , wherein the switch is included in the integrated circuit controller. 
     
     
         5 . The power converter of  claim 1 , wherein the plurality of linear functions includes a first linear function, a second linear function and a third linear function, wherein the duty cycle of the drive signal is adjusted in response to the first linear function when the feedforward signal is below a first threshold value, wherein the duty cycle of the drive signal is adjusted in response to the second linear function when the feedforward signal is between the first threshold value and a second threshold value, and wherein the duty cycle of the drive signal is a adjusted in response to the third linear function when the feedforward signal is between the second threshold value and a third threshold value. 
     
     
         6 . The power converter of  claim 5 , wherein a slope of the first linear function is substantially zero, and wherein a slope of the second linear function is non-zero. 
     
     
         7 . The power converter of  claim 6 , wherein the slope of the second linear function is a linear reduction of the duty cycle as the feedforward signal increases. 
     
     
         8 . The power converter of  claim 1 , further comprising a bulk capacitor coupled to an input of the power converter, wherein the dc input voltage is a voltage across the bulk capacitor. 
     
     
         9 . An integrated circuit controller for use in a power converter, the integrated circuit controller comprising:
 a gain selector circuit coupled to select a gain multiplier according to a value of a feedforward signal that is representative of a direct-current (DC) input voltage of the power converter, wherein the gain selector circuit is further coupled to apply the gain multiplier to the feedforward signal to generate a duty cycle adjust signal; and   a switch duty cycle controller coupled to generate a drive signal to control switching of a switch to regulate an output of the power converter in response to a feedback signal, wherein a duty cycle of the drive signal is varied in response to the duty cycle adjust signal such that the duty cycle varies according to a plurality of linear functions over a range of values of the feedforward signal.   
     
     
         10 . The integrated circuit controller of  claim 9 , wherein the switch is included in the integrated circuit controller. 
     
     
         11 . The integrated circuit controller of  claim 9 , wherein the plurality of linear functions includes a first linear function, a second linear function and a third linear function, wherein the duty cycle of the drive signal is adjusted in response to the first linear function when the feedforward signal is below a first threshold value, wherein the duty cycle of the drive signal is adjusted in response to the second linear function when the feedforward signal is between the first threshold value and a second threshold value, and wherein the duty cycle of the drive signal is a adjusted in response to the third linear function when the feedforward signal is between the second threshold value and a third threshold value. 
     
     
         12 . The integrated circuit controller of  claim 11 , wherein a slope of the first linear function is substantially zero, and wherein a slope of the second linear function is non-zero. 
     
     
         13 . The integrated circuit controller of  claim 12 , wherein the slope of the second linear function is a linear reduction of the duty cycle as the feedforward signal increases. 
     
     
         14 . An integrated circuit controller for use in a power converter, the integrated circuit controller comprising:
 a gain selector circuit coupled to select a gain multiplier according to a value of a feedforward signal that is representative of a direct-current (DC) input voltage of the power converter, wherein the gain selector circuit is further coupled to apply the gain multiplier to the feedforward signal to generate a duty cycle adjust signal; and   a switch duty cycle controller coupled to generate a drive signal to control switching of a switch to regulate an output of the power converter in response to a feedback signal and in response to the duty cycle adjust signal, wherein a maximum duty cycle of the drive signal and a duty cycle are varied in response to the duty cycle adjust signal, such that the maximum duty cycle varies according to a plurality of linear functions over a range of values of the feedforward signal and the duty cycle for a fixed value of the feedback signal varies according to the plurality of linear functions over the range of values of the feedforward signal.   
     
     
         15 . The integrated circuit controller of  claim 14 , wherein the switch is included in the integrated circuit controller. 
     
     
         16 . The integrated circuit controller of  claim 14 , wherein the plurality of linear functions includes a first linear function, a second linear function and a third linear function, wherein the duty cycle for the fixed value of the feedback signal and the maximum duty cycle of the drive signal are adjusted in response to the first linear function when the feedforward signal is below a first threshold value, wherein the duty cycle for the fixed value of the feedback signal and the maximum duty cycle of the drive signal are adjusted in response to the second linear function when the feedforward signal is between the first threshold value and a second threshold value, and wherein the duty cycle for the fixed value of the feedback signal and the maximum duty cycle of the drive signal are adjusted in response to the third linear function when the feedforward signal is between the second threshold value and a third threshold value. 
     
     
         17 . The integrated circuit controller of  claim 14 , wherein a slope of the first linear function is substantially zero, and wherein a slope of the second linear function is non-zero.