Synchronous rectifier having precise on/off switching times

An offset regulating loop for a synchronous rectifier, the offset regulating loop comprising:

• a comparator having an offset control input, the comparator adapted to sense a current flowing through an energy storage element of the synchronous rectifier, wherein the comparator is configured to provide a signal for opening a controlled switch in a current recirculation loop for the energy storage element at a selected time before current in the current recirculation loop falls to a zero value;
• a timing detector adapted to receive an output signal from the comparator;
• at least one current source configured to receive a control signal from the timing detector;
• and
• an integrator configured to receive current from the at least one current source and provide an integrated signal to the offset control input of the comparator,
• wherein the timing detector is adapted to provide a first control signal to a first current source of the at least one current source for a first time interval before current flowing through the energy storage element falls to a zero value, and the timing detector is adapted to provide a second control signal to a second current source of the at least one current source for a second time interval after current flowing through the energy storage element falls to a zero value, and
• wherein the integrated signal adjusts an offset of the comparator in a manner to maintain the first and second time intervals at approximately equal values.

A synchronous rectifier comprising:

• an energy storage element having a first terminal;
• and
• an offset regulating loop comprising:
• a comparator having an offset control input, the comparator adapted to sense a current flowing through the energy storage element, wherein the comparator is configured to provide a signal for opening a controlled switch in a current recirculation loop for the energy storage element at a selected time before current in the current recirculation loop falls to a zero value;
• a timing detector adapted to receive an output signal from the comparator;
• at least one current source configured to receive a control signal from the timing detector;
• and
• an integrator configured to receive current from the at least one current source and provide an integrated signal to the offset control input of the comparator,
• wherein the timing detector is adapted to provide a first control signal to a first current source of the at least one current source for a first time interval before current flowing through the energy storage element falls to a zero value, and the timing detector is adapted to provide a second control signal to a second current source of the at least one current source for a second time interval after current flowing through the energy storage element falls to a zero value;
• and
• wherein the integrated signal adjusts an offset of the comparator in a manner to maintain the first and second time intervals at approximately equal values.

A method for controlling switching of a synchronous rectifier comprising an energy storage element, comprising:

• coupling a first terminal of the energy storage element to a power supply input in a first time interval;
• coupling the first terminal of the energy storage element to a reference line in a second time interval;
• detecting a current flowing in the energy storage element using a comparator having an offset control input;
• decoupling the first terminal of the energy storage element from the reference line at a selected time before the current falls to a zero value responsive to detecting a selected current value in the energy storage element;
• receiving, by a timing detector, an output signal from the comparator;
• providing a first control signal from the timing detector to a first current source for a first time interval before current flowing through the energy storage element falls to a zero value;
• providing a second control signal from the timing detector to a second current source for a second time interval after current flowing through the energy storage element falls to a zero value;
• integrating current from the first and second current source to produce an integrated signal;
• and
• providing the integrated signal to the offset control input of the comparator,
• wherein the integrated signal adjusts the offset of the comparator in a manner to maintain the first and second time intervals at approximately equal values.

A synchronous rectifier comprising:

• an energy storage element having a first terminal;
• and
• an offset regulating loop comprising:
• means to detect current flowing in an energy storage element of the synchronous rectifier;
• and
• means to open a controlled switch in a current recirculation loop for the energy storage element at a selected time before current in the current recirculation loop falls to a zero value, the means to open being responsive to the means to detect current flowing in the energy storage element,
• wherein the means to detect comprises a comparator having an offset control input;
• wherein the means to open comprises a first and a second current source, wherein the first current source is configured to provide a first current to an integrator for a first time interval before the current flowing in the energy storage element falls to a zero value, and the second current source is configured to provide a second current of opposite polarity to the first current to the integrator for a second time interval after the current flowing in the energy storage element falls to a zero value;
• wherein the integrator is configured to provide an integrated signal to the offset control input of the comparator;
• and
• wherein the integrated signal adjusts an offset of the comparator in a manner to maintain the first and second time intervals at approximately equal values.