System and method for a primary feedback switched mode power supply

Abstract

A primary side controlled power converter having a voltage sensing means coupled to a transformer of the power converter and configured to provide a voltage feedback waveform representative of an output of the transformer is provided. A primary switching circuit operates to control energy storage of a primary side of the transformer. The primary switching circuit is operable during an on time and inoperable during an off time. The on and off time is switched at a system frequency. A feedback amplifier generates an error signal indicative of a difference between the voltage feedback waveform and a reference voltage. A sample and hold circuit samples the error signal at a periodic frequency during the off time. An error signal amplifier is configured to provide the sampled value to the primary switching circuit wherein the primary switching circuit controls the transformer and thereby regulates an output of the power converter.

1 - 36 . (canceled) 
   
   
       37 . A power converter comprising:
 a switching circuit that controls a current flowing through a primary winding of a transformer based on a sampled error signal, wherein the current flows through the primary winding during an on time and does not flow through the primary winding during an off time, wherein the switching circuit regulates an output voltage of the power converter by adjusting the on time and the on time plus the off time, and wherein energy is transferred from the primary winding to the secondary winding during the off time.   
   
   
       38 . The power converter of  claim 37 , wherein the switching circuit includes a power switch that conducts the current flowing through the primary winding to a ground terminal during the on time. 
   
   
       39 . The power converter of claim  388 , wherein the power switch is a field-effect transistor. 
   
   
       40 . The power converter of claim  388 , wherein the power switch is coupled to an emitter of a bipolar transistor. 
   
   
       41 . The power converter of  claim 37 , further comprising:
 a load regulation compensation circuit that reduces variation in the output voltage of the power converter as an output load current increases.   
   
   
       42 . The power converter of claim  411 , wherein the load regulation compensation circuit compensates for a series resistance at an output of the power converter. 
   
   
       43 . The power converter of claim  411 , wherein the load regulation compensation circuit adjusts the difference between the feedback voltage and the reference voltage by an amount dependent on the current flowing through the primary winding. 
   
   
       44 . The power converter of  claim 37 , further comprising:
 a feedback sample-and-hold circuit that includes a plurality of capacitors, wherein the sampled error signal is derived from a voltage across one of the plurality of capacitors.   
   
   
       45 . An integrated circuit comprising:
 a feedback terminal on which a feedback voltage is present, wherein the feedback voltage depends on a voltage across a secondary winding of a transformer; and   means for controlling a current flowing through a primary winding of the transformer, wherein the current flows through the primary winding during an on time and does not flow through the primary winding during an off time, wherein the switching circuit regulates an output voltage of the power converter by adjusting the on time and the on time plus the off time, and wherein energy is transferred from the primary winding to a secondary winding of the transformer during the off time.   
   
   
       46 . The integrated circuit of  claim 45 , further comprising:
 a load regulation compensation circuit that adjusts the output voltage of the power converter to compensate for a series resistance at an output of the power converter.   
   
   
       47 . The integrated circuit of  claim 45 , wherein the feedback terminal is coupled to a resistor divider that is coupled to a winding of the transformer that is not the primary winding. 
   
   
       48 . A method for regulating an output voltage of a flyback converter, comprising:
 switching a current flowing through a primary winding of a transformer of the flyback converter, wherein the current flows-through the primary winding during an on time and does not flow through the primary winding during an off time;   generating a sampled error signal; and   regulating an output voltage of the flyback converter by adjusting the on time and the on time plus the off time based on the sampled error signal.   
   
   
       49 . The method of claim  4848 , wherein the current flowing through the primary winding during the on time passes through a ground terminal. 
   
   
       50 . The method of  claim 48 , wherein the error signal is held during the off time just prior to when a current flowing though a winding on a secondary side of the transformer discharges to zero. 
   
   
       51 . The method of  claim 48 , further comprising:
 compensating for an increase in an output load current so as to reduce variations in the output voltage of the flyback converter.   
   
   
       52 . The method of  claim 51 , wherein the compensating includes adjusting the difference between a feedback voltage and a reference voltage by an amount dependent on the current flowing through the primary winding. 
   
   
       53 . The method of  claim 48 , further comprising:
 reducing electromagnetic interference emissions by uttering the frequency at which the current flowing through the primary winding is switched.   
   
   
       54 . The method of  claim 48 , further comprising:
 adjusting the frequency at which the current flowing through the primary winding is switched proportionally to the output voltage.   
   
   
       55 . The method of  claim 48 , further comprising:
 adjusting the frequency at which the current flowing through the primary winding is switched proportionally to a feedback voltage when the feedback voltage is below a reference voltage.   
   
   
       56 . The method of  claim 48 , further comprising:
 reducing the frequency at which the current flowing through the primary winding is switched when the sampled error signal is indicative of a light load on the flyback converter.