Transformer communication system

Abstract

A power converter includes a transformer coupled to transfer power from a primary side of the power converter to a secondary side of the power converter. The transformer includes a primary side winding coupled to receive power from a primary side input of the power converter and a secondary side winding coupled to provide power to a secondary side output of the power converter. A power switch is coupled to the transformer, and a power switch controller is coupled to control the switching of the power switch between an ON state and an OFF state. A communication circuit is coupled to communicate data between the primary side of the power converter and the secondary side of the power converter.

What is claimed is: 
     
         1 . A power converter comprising:
 a transformer coupled to transfer power from a primary side of the power converter to a secondary side of the power converter, the transformer including:
 a primary-side winding coupled to receive power from a primary side input of the power converter; and 
 a secondary-side winding coupled to provide power to a secondary-side output of the power converter; 
   a power switch coupled to the transformer;   a power switch controller coupled to control the switching of the power switch between an ON state and an OFF state; and   a communication circuit coupled to communicate data between the primary side of the power converter and the secondary side of the power converter.   
     
     
         2 . The power converter of  claim 1 , wherein communication circuit comprises:
 a communication switch coupled to the secondary-side winding,   a communication controller to control switching of the communication switch coupled to communicate data; and   a detector coupled to detect data communicated from the secondary-side winding.   
     
     
         3 . The power converter of  claim 1 , wherein time during which the power switch is in the OFF state includes an idle ring. 
     
     
         4 . The power converter of  claim 3 , wherein the idle ring is triggered by a transition from a non-zero secondary current to a substantially zero current at the secondary-side output. 
     
     
         5 . The power converter of  claim 4 , wherein the detector is coupled to detect a delay in the idle ring to detect said data. 
     
     
         6 . The power converter of  claim 3 , wherein the communication switch coupled to modulate the idle ring to communicate said data, wherein the modulation is an amplitude modulation, and wherein the detector is coupled to detect a change of amplitude of the idle ring to thereby detect said data. 
     
     
         7 . The power converter of  claim 6 , wherein the detector is coupled to an auxiliary winding on the primary side, wherein the auxiliary winding is coupled to receive the data communicated from the secondary-side. 
     
     
         8 . The power converter of  claim 6 , wherein the power converter further comprises an auxiliary power supply circuit coupled to the primary side input to the power converter, wherein the auxiliary power supply circuit is coupled to use the auxiliary winding to power the primary switch controller. 
     
     
         9 . The power converter of  claim 8 , wherein the power converter is coupled to interrupt operation with continuous conduction switching cycles when substantially zero current flows from the secondary-side winding to the secondary-side output. 
     
     
         10 . The power converter of  claim 9 , wherein the power converter is coupled to operate in discontinuous conduction mode when substantially zero current flows from the secondary-side winding to the secondary-side output in substantially all switching cycles. 
     
     
         11 . The power converter of  claim 1 , wherein the power converter is a forward converter. 
     
     
         12 . The power converter of  claim 1 , wherein the power converter is a switched mode power supply. 
     
     
         13 . A method for transferring information in a power converter, wherein the power converter comprises:
 a transformer coupled to transfer power from a primary side of the power converter to a secondary side of the power converter, wherein the transformer includes a primary side winding coupled to receive power from a primary side input of the power converter, and a secondary side winding coupled to provide power to a secondary side output of the power converter;   a power switch coupled to the transformer;   a power switch controller coupled to control switching of the power switch between an ON state and an OFF state; and   a communication circuit coupled to communicate data between the primary side and the secondary side of the power converter, wherein the communication circuit includes a communication switch coupled to the secondary side winding, a communication controller to control switching of the communication switch coupled to communicate data, and a detector coupled to detect data communicated from the secondary-side winding,   wherein the method comprises:
 switching the power switch with the power switch controller between the ON state and the OFF state to control the power transfer from the primary side to the secondary side of the power converter, wherein at least some switching cycles include an idle ring when a current from the secondary side winding to the secondary side output is substantially zero; 
 switching the communication switch with the communication controller to modulate the idle ring and communicate the data from the secondary side to the primary side of the power converter; 
 detecting the switching of the secondary-side communication switch with the detector; and 
 demodulating the detection of the switching. 
   
     
     
         14 . The method of  claim 13 , wherein said detecting the switching of the communication switch comprises detecting a delay in the idle ring with the detector. 
     
     
         15 . The method of  claim 13 , wherein said switching the communication switch with the communication controller to modulate the idle ring comprises amplitude modulating the idle ring, and wherein said detecting the switching of the secondary-side communication switch with the detector comprises detecting a change of amplitude of the idle ring with the detector. 
     
     
         16 . The method of  claim 13 , wherein during at least some switching cycles a time during which the primary-side power switch is in the OFF state includes a first portion during which current flows from the secondary-side winding to the secondary-side output and a second portion during which substantially zero current flows from the secondary-side winding to the secondary-side output, wherein said switching the power switch with the power switch controller between the ON state and the OFF state to control the power transfer from the primary side to the secondary side of the power converter comprises operating the power converter in a discontinuous conduction mode in which the second portion occurs in substantially all switching cycles. 
     
     
         17 . The method of  claim 16 , further comprising powering the power switch controller using an auxiliary winding of an auxiliary power supply circuit coupled to the primary-side input to the power converter, wherein the auxiliary power supply circuit is coupled to use the auxiliary winding to power the power switch controller. 
     
     
         18 . The method of  claim 13 , further comprising interrupting operation with continuous conduction switching cycles. 
     
     
         19 . The method of  claim 18 , further comprising interrupting operation in at least some switching cycles when substantially zero current flows from the secondary-side winding to the secondary-side output.