Simple control circuit for synchronous rectifiers used in zvs phase shifted full bridge converter

A switching power converter, comprising:

• an input voltage source;
• a transformer having a primary winding and a secondary winding;
• a switching circuit connected to the primary winding of the transformer for providing bidirectional current flow there through, the switching circuit having a first pair and a second pair of diagonal switching devices;
• a rectifying circuit, having two synchronous rectifiers, connected to the secondary winding of the transformer for providing an output voltage of the converter;
• a primary control circuit connected to the switching circuit and operable to generate drive signals for the switching device, such that each pair of diagonal switching devices conduct alternately with a dead time period therebetween and the dead time period is initiated when one of the conducting diagonal switching devices is driven to an off state;
• and
• a secondary control circuit connected to the rectifying circuit and operable to drive the two synchronous rectifiers to an on state during the dead time period, such that one of the conducting diagonal switching devices is driven to an off state prior to the second of the two synchronous rectifiers being driven to an on state.

A switching power converter, comprising:

• an input voltage source;
• a switching circuit having a first switching device and a second switching device connected in series to form a first switching leg, and a third switching device and a fourth switching device connected in series to form a second switching leg, each of the switching legs connected in parallel with the input voltage source;
• a transformer having a primary winding and a secondary winding, one end of the primary winding being connected to a junction point between the first switching device and the second switching device and the other end of the primary winding being connected to a junction point between the third switching device and the fourth switching device;
• a rectifying circuit, having two synchronous rectifiers, connected to the secondary winding of the transformer for providing an output voltage of the converter;
• a primary control circuit connected to the switching circuit, the primary control circuit operable to supply substantially complementary control signals to the switching devices in one of the switching legs and relatively phase shifted substantially complementary control signals to the switching devices in the other switching legs, so that diagonal switching devices conduct alternately with a dead time period therebetween and the dead time period is initiated when one of the conducting diagonal switching devices is driven to an off state;
• and
• a secondary control circuit connected to the rectifying circuit, the secondary control circuit operable to drive the two synchronous rectifiers to an on state during the dead time period, such that said one of the conducting diagonal switching devices is driven to an off state by the primary control circuit prior to the second of the two synchronous rectifiers being driven to an on state.

A switching power converter, comprising:

• an input voltage source;
• a switching circuit having a first switching device and a second switching device connected in series to form a first switching leg, and a third switching device and a fourth switching device connected in series to form a second switching leg, each of the switching legs connected in parallel with the input voltage source;
• a transformer having a primary winding and a secondary winding, one end of the primary winding being connected to a junction point between the first switching device and the second switching device and the other end of the primary winding being connected to a junction point between the third switching device and the fourth switching device;
• a rectifying circuit, having two synchronous rectifiers, connected to the secondary winding of the transformer for providing an output voltage of the converter;
• a primary control circuit connected to the switching circuit and operable to generate a drive signal for each of the switching devices;
• and
• a secondary control circuit having a first logic OR gate and a second logic OR gate, the first OR gate receives the drive signals used to control the first and fourth switching devices and outputs a drive signal to one of the two synchronous rectifiers, and the second OR gate receives the drive signals used to control the second and third switching devices and outputs a drive signal to the other of the two synchronous rectifiers.