Power converter and method of control thereof

Abstract

A flyback power converter includes a hybrid clamp circuit and a corresponding power management unit that substantially optimizes the performance of the flyback power converter in its entire line and load ranges. The clamp circuit, which is connected in parallel to a primary winding of the flyback transformer, includes a parallel combination of a capacitor and resistor that is connected in series with a parallel combination of a switch and a diode. By sensing the operating conditions, the power management circuit configures the clamp circuit either as a passive clamp or as an active clamp. In the passive-clamp configuration, the switch is kept turned off. In the active-clamp configuration, the switch operates with pulse-width modulation (PWM) which enables ZVS turn-on of the main switch.

We claim: 
     
       1. A flyback power converter receiving an input voltage and providing an output voltage and an output current to a load, comprising:
 a transformer having a primary winding and a secondary winding, the output voltage and the output current being provided to the load from the secondary winding; 
 a first switch coupled to the primary winding, the first switch coupling the input voltage across the primary winding when the first switch is turned on; 
 a clamp circuit comprising first and second parallel circuits coupled to each other in series, wherein the first parallel circuit comprises a second switch and a clamp diode, and wherein the second parallel circuit comprises a clamp capacitor and a clamp resistor, such that the clamp circuit to provide an active clamp or a passive clamp, according to whether the second switch is closed or open; 
 a controller configured to provide a first control signal for regulating the output voltage or the output current by periodically turning on and off the first switch and a second control signal for the second switch; and 
 a power management unit configured to provide an enable/disable signal for enabling or disabling switching of the second switch by the second control signal based on the flyback power converter's operating conditions, 
 wherein the clamp circuit is configured to: 
 if the flyback power converter's operating conditions specify an active clamp, the second switch is enabled by the second control signal and both the first switch and the second switch are modulated by the first control signal and the second control signal, respectively, to provide the active clamp, such that energy stored in a leakage inductance of the flyback power converter is at least partially recycled and used to achieve zero-voltage-switching (ZVS) for the first switch; and 
 if the flyback power converter's operating conditions specify a passive clamp, the second switch is disabled by the second control signal and the first switch is modulated by the first control signal, to provide the passive clamp, such that the energy stored in the leakage inductance of the flyback power converter is dissipated in the clamp resistor. 
 
     
     
       2. The flyback power converter of  claim 1 , wherein the power management unit keeps the second switch continuously off for a subset of the operating conditions. 
     
     
       3. The flyback power converter of  claim 1  wherein the operating conditions are determined based on at least one of the input voltage, a current through the first switch, the output voltage, the output current, and a switching frequency. 
     
     
       4. The flyback power converter of  claim 3 , further comprising a rectifier coupling the secondary winding to the load, wherein the operating conditions are further determined based on a current through the rectifier. 
     
     
       5. The flyback power converter of  claim 1 , wherein the flyback power converter operates in continuous-conduction mode, discontinuous-conduction mode, or at a boundary between the continuous-conduction mode and discontinuous-conduction mode. 
     
     
       6. The flyback power converter of  claim 1 , wherein the power management unit optimizes at least one of: converter efficiency, component stress, electro-magnetic-interference (EMI) performance, and transformer performance. 
     
     
       7. The flyback power converter of  claim 1 , wherein the power management unit selects the flyback power converter to operate in one of: a continuous-conduction mode, a discontinuous-conduction mode, or at a boundary between the continuous-conduction mode and discontinuous-conduction mode of operation based on the operating conditions. 
     
     
       8. The flyback power converter of  claim 1 , wherein the first switch and the second switch are not simultaneously turned on during operation. 
     
     
       9. The flyback power converter of  claim 1 , wherein the clamp circuit is coupled in parallel to the primary winding of the transformer. 
     
     
       10. The flyback power converter of  claim 1 , wherein the clamp circuit is coupled in parallel to the first switch. 
     
     
       11. The flyback power converter of  claim 1 , wherein the first switch is turned on at zero voltage or, when the input voltage is greater than N times the output voltage, at a voltage that substantially equals to a difference between the input voltage and N times the output voltage, N being the ratio of the number of primary-winding turns to the number of secondary-winding turns. 
     
     
       12. The flyback power converter of  claim 1 , wherein a body diode of the second switch serves as the clamp diode. 
     
     
       13. The flyback power converter of  claim 1 , further comprising a filter capacitor connected in parallel across the load, and wherein the filter capacitor and the load are coupled to the secondary winding of the transformer. 
     
     
       14. The flyback power converter of  claim 13 , wherein the filter capacitor and the load are coupled to the secondary winding of the transformer by a rectifier diode. 
     
     
       15. The flyback power converter of  claim 13 , wherein filter capacitor and the load are coupled to the secondary winding of the transformer by a third switch. 
     
     
       16. The flyback power converter of  claim 15 , wherein the third switch provides rectification. 
     
     
       17. The flyback power converter of  claim 1 , wherein the first switch turns on at a valley of a voltage across the first switch at a time when the second switch is disabled. 
     
     
       18. The flyback power converter of  claim 1 , wherein the second switch turns on at a peak of the voltage across the first switch. 
     
     
       19. The flyback power converter of  claim 1 , wherein at least one of the first and second switch comprises a GaN switch or a SiC switch. 
     
     
       20. The flyback power converter of  claim 1 , wherein the second switch comprises an enhancement mode GaN switch. 
     
     
       21. The flyback power converter of  claim 20 , wherein the GaN switch carries a reverse current by reverse conduction of the switch. 
     
     
       22. A flyback power converter receiving an input voltage and providing an output voltage and an output current to a load, comprising:
 a transformer having a primary winding and a secondary winding, the output voltage and the output current being provided to the load from the secondary winding;   a first switch coupled to the primary winding, the first switch coupling the input voltage across the primary winding when the first switch is turned on;   a clamp circuit comprising a second switch, a clamp capacitor, and a clamp resistor, the clamp resistor being connected with the clamp capacitor in parallel and being connected with the second switch in series; and   a control block comprising a controller and a power management unit and configured to provide a first control signal for regulating the output voltage or the output current by periodically turning on and off the first switch and a second control signal for the second switch for enabling or disabling switching of the second switch based on the flyback power converter's operating conditions,   wherein the clamp circuit is configured to:
 if the flyback power converter's operating conditions specify an active clamp, the second switch is enabled by the second control signal and both the first switch and the second switch are modulated by the first control signal and the second control signal, respectively, to provide the active clamp, such that energy stored in a leakage inductance of the flyback power converter is at least partially recycled and used to achieve zero-voltage-switching (ZVS) for the first switch; and 
 if the flyback power converter's operating conditions specify a passive clamp, the second switch is disabled by the second control signal and the first switch is modulated by the first control signal, to provide the passive clamp, such that the energy stored in the leakage inductance of the flyback power converter is dissipated in the clamp resistor.  
   
     
     
       23. The flyback power converter of  claim 22  wherein the operating conditions are determined based on at least one of the input voltage, a current through the first switch, the output voltage, the output current, and a switching frequency.  
     
     
       24. The flyback power converter of  claim 23 , further comprising a rectifier coupling the secondary winding to the load, wherein the operating conditions are further determined based on a current through the rectifier.  
     
     
       25. The flyback power converter of  claim 22 , wherein the control block optimizes at least one of: converter efficiency, component stress, electro-magnetic-interference (EMI) performance, and transformer performance.  
     
     
       26. The flyback power converter of  claim 22 , wherein the first switch and the second switch are not simultaneously turned on during operation.  
     
     
       27. The flyback power converter of  claim 22 , wherein the first switch is turned on at zero voltage or, when the input voltage is greater than N times the output voltage, at a voltage that substantially equals to a difference between the input voltage and N times the output voltage, N being the ratio of the number of primary-winding turns to the number of secondary-winding turns.  
     
     
       28. The flyback power converter of  claim 22 , wherein the first switch turns on at a valley of a voltage across the first switch at a time when the second switch is disabled.  
     
     
       29. The flyback power converter of  claim 22 , wherein the second switch turns on at a peak of the voltage across the first switch.  
     
     
       30. The flyback power converter of  claim 22 , wherein the second switch is selected from at least one of a MOSFET switch, a GaN switch, and a SiC switch.  
     
     
       31. A flyback power converter receiving an input voltage and providing an output voltage and an output current to a load, comprising:
 a transformer having a primary winding and a secondary winding, the output voltage and the output current being provided to the load from the secondary winding;   a first switch coupled to the primary winding, the first switch coupling the input voltage across the primary winding when the first switch is turned on;   a clamp circuit, coupled to the primary winding, comprising a second switch and a passive circuit with a resistor;   a controller configured to provide a first control signal for regulating the output voltage or the output current by periodically turning on and off the first switch and a second control signal for the second switch; and   a power management unit configured to provide an enable/disable signal for enabling or disabling switching of the second switch by the second control signal based on the flyback power converter's operating conditions, wherein the clamp circuit is configured to:
 if the flyback power converter's operating conditions specify an active clamp, the second switch is enabled by the second control signal and both the first switch and the second switch are modulated by the first control signal and the second control signal, respectively, to provide the active clamp, such that energy stored in a leakage inductance of the flyback power converter is at least partially recycled and used to achieve zero-voltage-switching (ZVS) for the first switch; and 
 if the flyback power converter's operating conditions specify a passive clamp, the second switch is disabled by the second control signal and the first switch is modulated by the first control signal, to provide the passive clamp, such that the energy stored in the leakage inductance of the flyback power converter is dissipated in the clamp resistor.  
   
     
     
       32. The flyback power converter of  claim 31  wherein the operating conditions are determined based on at least one of the input voltage, a current through the first switch, the output voltage, the output current, and a switching frequency.  
     
     
       33. The flyback power converter of  claim 32 , further comprising a rectifier coupling the secondary winding to the load, wherein the operating conditions are further determined based on a current through the rectifier.  
     
     
       34. The flyback power converter of  claim 31 , wherein the power management unit optimizes at least one of: converter efficiency, component stress, electro-magnetic-interference (EMI) performance, and transformer performance.  
     
     
       35. The flyback power converter of  claim 31 , wherein the first switch and the second switch are not simultaneously turned on during operation.  
     
     
       36. The flyback power converter of  claim 31 , wherein the first switch is turned on at zero voltage or, when the input voltage is greater than N times the output voltage, at a voltage that substantially equals to a difference between the input voltage and N times the output voltage, N being the ratio of the number of primary-winding turns to the number of secondary-winding turns.  
     
     
       37. The flyback power converter of  claim 31 , wherein the first switch turns on at a valley of a voltage across the first switch at a time when the second switch is disabled.  
     
     
       38. The flyback power converter of  claim 31 , wherein the second switch turns on at a peak of the voltage across the first switch.  
     
     
       39. The flyback power converter of  claim 31 , wherein the second switch is selected from at least one of a MOSFET switch, a GaN switch, and a SiC switch.  
     
     
       40. The flyback power converter of  claim 1 , wherein the power management unit provides information to the controller to specify a mode of operation.  
     
     
       41. The flyback power converter of  claim 22 , wherein the control block provides information to specify a mode of operation.  
     
     
       42. The flyback power converter of  claim 31 , wherein the power management unit provides information to the controller to specify a mode of operation.