Control of asymmetric parallel synchronous rectifiers in power converter topologies

A power converter, comprising:

• an input power source;
• a synchronous rectifier comprising a plurality of actively controlled switches coupled in parallel and configured to rectify current delivered from the input power source to a load;
• and
• a controller operable to issue a first control signal for driving a first one of the actively controlled switches and issue a second control signal for driving a second one of the actively controlled switches, the first control signal being a different control signal than the second control signal so that the first actively controlled switch is controllable separately from the second actively controlled switch,
• wherein the first actively controlled switch has a higher current-carrying capacity than the second actively controlled switch,
• wherein each actively controlled switch comprises one or more transistors in parallel,
• wherein the second actively controlled switch comprises fewer transistors in parallel than the first actively controlled switch, so that the first actively controlled switch has a higher current rating than the second actively controlled switch.

A power converter, comprising:

• an input power source;
• a synchronous rectifier comprising a plurality of actively controlled switches coupled in parallel and configured to rectify current delivered from the input power source to a load;
• and
• a controller operable to issue a first control signal for driving a first one of the actively controlled switches and issue a second control signal for driving a second one of the actively controlled switches, the first control signal being a different control signal than the second control signal so that the first actively controlled switch is controllable separately from the second actively controlled switch,
• wherein the first actively controlled switch has a higher current-carrying capacity than the second actively controlled switch,
• wherein the power converter is a buck converter comprising a high-side switch configured to couple the input power source to the load through an inductor when the high-side switch is on,
• wherein the synchronous rectifier is configured as a low-side switch of the buck converter for coupling the load to ground through the inductor when the low-side switch is on,
• wherein each switching cycle of the buck converter has an energy transfer period during which the high-side switch is on and the low-side switch is off, and a freewheeling period during which the high-side switch is off and the low-side switch is on,
• wherein during each freewheeling period, the controller is operable to activate the first control signal for the entire freewheeling period and activate the second control signal for only part of the freewheeling period.

A power converter, comprising:

• an input power source;
• a synchronous rectifier comprising a plurality of actively controlled switches coupled in parallel and configured to rectify current delivered from the input power source to a load;
• a transformer for isolating the input power source from the load;
• and
• a controller operable to issue a first control signal for driving a first one of the actively controlled switches and issue a second control signal for driving a second one of the actively controlled switches, the first control signal being a different control signal than the second control signal so that the first actively controlled switch is controllable separately from the second actively controlled switch,
• wherein the first actively controlled switch has a higher current-carrying capacity than the second actively controlled switch,
• wherein the synchronous rectifier is coupled to a winding of the transformer,
• wherein the power converter is a resonant converter,
• wherein each switching cycle of the synchronous rectifier has a variable switching frequency determined by the controller based on changes at the input power source and changes at the load,
• wherein the controller is operable to decrease the variable switching frequency of the synchronous rectifier during full power conditions at the load,
• wherein the controller is operable to activate the first control signal for half the switching cycle during the full power conditions at the load,
• wherein the controller is operable to activate the second control signal for less than half the switching cycle during the full power conditions at the load.