Method and apparatus for on/off control of a power converter

Abstract

A power converter includes an energy transfer element coupled between a power converter input and a power converter output. A power switch is coupled to the energy transfer element and the power converter input. A feedback sampling circuit is coupled to receive a feedback signal representative of the power converter output to generate at least one feedback signal sample during each switching cycle. A switch conduction scheduling circuit is coupled to set a number of enabled cycles and a number of disabled cycles of the power switch in a plurality of future switching cycles in response to the feedback signal samples for each present switching cycle and one or more past switching cycles. A switch conduction control circuit is coupled to enable or disable conduction of the power switch during a switching cycle to control an amount of energy transferred from the power converter input to the power converter output.

What is claimed is: 
     
         1 . A power converter, comprising:
 an energy transfer element coupled between a power converter input and a power converter output;   a power switch coupled to the energy transfer element and the power converter input;   a feedback sampling circuit coupled to receive a feedback signal representative of the power converter output to generate at least one feedback signal sample during each switching cycle;   a switch conduction scheduling circuit coupled to set a number of enabled cycles and a number of disabled cycles of the power switch in a plurality of future switching cycles in response to the feedback signal samples for each present switching cycle and one or more past switching cycles; and   a switch conduction control circuit coupled to enable or disable conduction of the power switch during a switching cycle to control an amount of energy transferred from the power converter input to the power converter output.   
     
     
         2 . The power converter of  claim 1  wherein the switch conduction scheduling circuit is coupled to increase the number of disabled cycles of the power switch in the plurality of future switching cycles in response to a decrease in a load coupled to power converter output. 
     
     
         3 . The power converter of  claim 1  wherein the switch conduction scheduling circuit is coupled to decrease the number of disabled cycles of the power switch in the plurality of future switching cycles in response to an increase in a load coupled to power converter output. 
     
     
         4 . The power converter of  claim 1  wherein the switch conduction scheduling circuit comprises a state machine coupled to set the number of enabled cycles and the number of disabled cycles of the power switch in the plurality of future switching cycles in response to the feedback signal samples for each present switching cycle and the one or more past switching cycles. 
     
     
         5 . The power converter of  claim 1  further comprising a current sense circuit coupled to the power switch to sense a current through the power switch. 
     
     
         6 . The power converter of  claim 5  wherein the current sense circuit is coupled to terminate conduction of power switch in response to the current through the power switch. 
     
     
         7 . The power converter of  claim 6  wherein the switch conduction scheduling circuit is coupled to adjust a current limit of the power switch in response to the feedback signal samples for each present switching cycle and one or more past switching cycles. 
     
     
         8 . The power converter of  claim 7  wherein the switch conduction scheduling circuit is coupled to decrease the current limit of the power switch in response to a decrease in a load coupled to power converter output. 
     
     
         9 . The power converter of  claim 7  wherein the switch conduction scheduling circuit is coupled to increase the current limit of the power switch in response to an increase in a load coupled to power converter output. 
     
     
         10 . The power converter of  claim 1  wherein the feedback sampling circuit includes a sampling signal generator coupled to generate a delay time from an end of a conduction of the power switch before the feedback signal samples are sampled.