Adaptive synchronous switching in a resonant converter

Abstract

An embodiment of a resonant converter includes having resonant circuitry having inductive and capacitive elements configured to create electrical resonance when an input voltage is applied and a synchronous rectifier coupled between at least a portion of the resonant circuitry and an output of the resonant converter. The synchronous rectifier includes a diode, and an electrical switch. Control circuitry is configured to operate the electrical switch such that the electrical switch is turned on when there is substantially no voltage across the diode and current flow in the diode is positive in a direction from anode to cathode.

1 . A resonant converter comprising:
 resonant circuitry having inductive and capacitive elements configured to create electrical resonance when an input voltage is applied;   a synchronous rectifier coupled between at least a portion of the resonant circuitry and an output of the resonant converter, the synchronous rectifier comprising:
 a diode, and 
 a first electrical switch; 
   first control circuitry configured to operate the first electrical switch such that the first electrical switch is turned on when there is substantially no voltage across the first diode and current flow in the first diode is positive in a direction from anode to cathode;   a second electrical switch, comprising the only electrical switch coupled between the input voltage and at least a portion of the resonant circuitry; and   second control circuitry configured to operate the second electrical switch such that the second electrical switch is turned on when there is substantially no voltage across the second electrical switch.   
     
     
         2 . The resonant converter of  claim 1  wherein the first electrical switch comprises a GaN transistor. 
     
     
         3 . The resonant converter of  claim 1  wherein the first control circuitry further comprises:
 a current transformer coupled to a current of at least a portion of the resonant circuitry; 
 an inverter amplifier coupled to the diode; and 
 an AND gate configured to perform a Boolean AND function using an output of the current transformer and an output of the inverter amplifier. 
 
     
     
         4 . The resonant converter of  claim 1 , wherein the resonant converter is a non-isolated resonant converter. 
     
     
         5 . The resonant converter of  claim 1 , wherein:
 the resonant converter is an isolated resonant converter having a transformer coupling an input stage with an output stage; and   the output stage comprises the synchronous rectifier.   
     
     
         6 . The resonant converter of  claim 1 , wherein:
 the output of the resonant converter has a positive rail and a negative rail; and   the synchronous rectifier is coupled in series between the resonant circuitry and the positive rail of the output of the resonant converter.   
     
     
         7 . The resonant converter of  claim 1 , wherein:
 the output of the resonant converter has a positive rail and a negative rail; and   the synchronous rectifier is coupled in series between the resonant circuitry and the negative rail of the output of the resonant converter.   
     
     
         8 . A resonant converter comprising:
 resonant circuitry having inductive and capacitive elements configured to create electrical resonance when an input voltage is applied;   a first synchronous rectifier and a second synchronous rectifier, wherein each of the first synchronous rectifier and the second synchronous rectifier comprise:
 a diode; and 
 an electrical switch in parallel with the diode; 
   first control circuitry configured to operate the first synchronous rectifier and the second synchronous rectifier such that, for each of the first synchronous rectifier and the second synchronous rectifier, the electrical switch is turned on when current flow in the diode is positive in a direction from anode to cathode; and   a resonant electrical switch, comprising the only electrical switch coupled between the input voltage and at least a portion of the resonant circuitry; and   second control circuitry configured to operate the resonant electrical switch such that the resonant electrical switch is turned on when there is substantially no voltage across the resonant electrical switch.   
     
     
         9 . The resonant converter of  claim 8  wherein the electrical switch of either or both of the first synchronous rectifier and the second synchronous rectifier comprises a GaN transistor. 
     
     
         10 . The resonant converter of  claim 8  further comprising a current transformer having:
 a primary winding configured to conduct a current of at least a portion of the resonant circuitry; 
 a first secondary winding configured to drive the electrical switch of the first synchronous rectifier; and 
 a second secondary winding, having an opposite polarity of the first secondary winding, configured to drive the electrical switch of the second synchronous rectifier. 
 
     
     
         11 . The resonant converter of  claim 10  wherein:
 the first secondary winding is configured to drive the electrical switch of the first synchronous rectifier via a first driver; and 
 the second secondary winding is configured to drive the electrical switch of the second synchronous rectifier via a second driver. 
 
     
     
         12 . The resonant converter of  claim 10  wherein the second secondary winding is further coupled to an output of the resonant converter. 
     
     
         13 . The resonant converter of  claim 8  wherein:
 an output of the resonant converter has a positive rail and a negative rail; and 
 the first synchronous rectifier is coupled in series between the resonant circuitry and the negative rail of the output of the resonant converter. 
 
     
     
         14 . The resonant converter of  claim 8  wherein:
 an output of the resonant converter has a positive rail and a negative rail; and 
 the first synchronous rectifier is coupled in series between the resonant circuitry and the positive rail of the output of the resonant converter.