Apparatus and method for detecting a change in output voltage of an isolated power converter

Abstract

A power converter controller includes a drive circuit coupled to control switching of a power switch to control a transfer of energy from an input of the power converter to an output of the power converter. A voltage sensor is coupled to the drive circuit to receive a feedback signal. The voltage sensor includes pulse sampler circuitry coupled to sample a first voltage representative of one of the peaks other than a first peak of ringing of the feedback signal in a first enabled switching cycle, sample a second voltage representative of the same peak of ringing of the feedback signal in a subsequent enabled switching cycle, and compare the sample of the first voltage with the sample of the second voltage and output a change signal based on the comparison. The drive circuit is further coupled to control switching of the power switch in response to the change signal.

What is claimed is: 
     
         1 . A power converter controller, comprising:
 a drive circuit coupled to control switching of a power switch coupled to an energy transfer element and to an input of the power converter to control a transfer of energy from the input of the power converter to an output of the power converter; and   a voltage sensor coupled to the drive circuit, the voltage sensor coupled to receive a feedback signal representative of the output of the power converter, the voltage sensor including a pulse sampler circuitry, wherein the pulse sampler circuitry is coupled to sample a first voltage representative of one of the peaks other than a first peak of ringing of the feedback signal in a first enabled switching cycle, wherein the pulse sampler circuitry is further coupled to sample a second voltage representative of the same peak of ringing of the feedback signal in a subsequent enabled switching cycle, wherein the pulse sampler circuitry is further coupled to compare the sample of the first voltage with the sample of the second voltage and output a change signal based on the comparison, and wherein the drive circuit is further coupled to control switching of the power switch in response to the change signal.   
     
     
         2 . The power converter controller of  claim 1  wherein the voltage sensor further includes a sample signal generator, wherein the sample signal generator is coupled to receive first and second control signals from the drive circuit to initiate first and second samplings of the feedback signal in the first and the subsequent enabled switching cycle, respectively, wherein the pulse sampler circuitry is coupled to sample the first voltage and the second voltage in response to the sample signal generator. 
     
     
         3 . The power converter controller of  claim 1  wherein the feedback signal is a reflected signal representative of the output of the power converter during an off state of the power switch. 
     
     
         4 . The power converter controller of  claim 1  wherein the feedback signal is coupled to be received from a bias winding that is magnetically coupled to an output winding of the energy transfer element. 
     
     
         5 . The power converter controller of  claim 1  wherein the ringing of the feedback signal is a positive ringing signal. 
     
     
         6 . The power converter controller of  claim 1  wherein the pulse sampler circuitry includes first and second capacitors coupled to store the sample of the first voltage and the sample of the second voltage, respectively. 
     
     
         7 . The power converter controller of  claim 6  wherein the pulse sampler circuitry includes a reset circuit coupled to reset the second capacitor after a predetermined time delay. 
     
     
         8 . The power converter controller of  claim 1  wherein the drive circuit is coupled to generate a switching signal responsive to the change signal and coupled to be received by the power switch to control the transfer of energy from the input of the power converter to the output of the power converter. 
     
     
         9 . A power converter, comprising:
 an energy transfer element coupled between an input of the power converter and an output of the power converter;   a power switch coupled to the energy transfer element and the input of the power converter;   a controller including a drive circuit coupled to generate a switching signal coupled to be received by the power switch to control a transfer of energy from the input of the power converter to the output of the power converter; and   a voltage sensor included in the controller and coupled to the drive circuit, the voltage sensor coupled to receive a feedback signal representative of the output of the power converter, the voltage sensor including a pulse sampler circuitry, wherein the pulse sampler circuitry is coupled to sample a first voltage representative of one of the peaks other than a first peak of ringing of the feedback signal in a first enabled switching cycle, wherein the pulse sampler circuitry is further coupled to sample a second voltage representative of the same peak of ringing of the feedback signal in a subsequent enabled switching cycle, and wherein the pulse sampler circuitry is further coupled to compare the sample of the first voltage with the sample of the second voltage and output a change signal to the drive circuit based on the comparison.   
     
     
         10 . The power converter of  claim 9  wherein the voltage sensor further includes a compare circuit coupled to compare the sample of the first voltage and the sample of the second voltage, the compare circuit coupled to output the change signal to the drive circuit in response to the comparison. 
     
     
         11 . The power converter of  claim 9  wherein the voltage sensor further includes a sample signal generator, wherein the sample signal generator is coupled to receive first and second control signals from the drive circuit to initiate first and second samplings of the feedback signal in the first and the subsequent enabled switching cycle, respectively, wherein the pulse sampler circuitry is coupled to sample the first voltage and the second voltage in response to the sample signal generator. 
     
     
         12 . The power converter controller of  claim 9  wherein the feedback signal is a reflected signal representative of the output of the power converter during an off state of the power switch. 
     
     
         13 . The power converter controller of  claim 9  wherein the feedback signal is coupled to be received from a bias winding that is magnetically coupled to an output winding of the energy transfer element. 
     
     
         14 . The power converter controller of  claim 9  wherein the ringing of the feedback signal is a positive ringing signal. 
     
     
         15 . The power converter controller of  claim 9  wherein the pulse sampler circuitry includes first and second capacitors coupled to store the first and second sample voltages, respectively. 
     
     
         16 . The power converter controller of  claim 15  wherein the pulse sampler circuitry includes a reset circuit coupled to reset the second capacitor after a predetermined time delay.