Synchronous rectifier drive and soft switching circuit
AssigneeTexas Instruments Incorporated
InventorIsaac Cohen
Life of this patent
Estimating the term…
Abstract
A circuit includes a synchronous rectifier that receives an alternating current (AC) voltage from a transformer secondary and provides a rectified direct current (DC) output voltage in response to a control input signal. A secondary rectifier switching circuit generates the control input signal. A current replica circuit generates a control voltage that replicates a current in the transformer secondary. The control voltage is employed to control switching of the secondary rectifier switching circuit based on the current in the transformer secondary. An offset circuit forces the control voltage in a predetermined direction to mitigate voltage error accumulations in the current replica circuit. A clamp circuit limits the control voltage to a predetermined voltage value.
Claims20
A circuit comprising:
- an output voltage terminal;
- a switch having a control terminal, a first terminal, and a second terminal coupled to the output voltage terminal;
- a voltage-to-current (VI) converter having a voltage input terminal coupled to the first terminal, and a current output terminal;
- a capacitor coupled to the current output terminal;
- and
- a secondary switching circuit having a control input terminal coupled to the capacitor and the current output terminal, and a control output terminal coupled to the control terminal of the switch.
A circuit comprising:
- an output voltage terminal;
- a transistor having a control terminal, a first terminal, and a second terminal coupled to the output voltage terminal;
- a voltage-to-current (VI) converter having a voltage input terminal coupled to the first terminal, and a current output terminal;
- a capacitor coupled between the current output terminal and a ground terminal;
- a reset comparator having a non-inverting input coupled to the ground terminal, an inverting input coupled to the capacitor and the current output terminal of the VI converter, and a reset output;
- and
- a flip-flop having a reset input coupled to the reset output of the reset comparator, and a non-inverting output coupled to the control terminal of the transistor.
A circuit comprising:
- input and output terminals;
- a transforming having a primary winding and a secondary winding;
- a primary rectifier coupled between the input terminal and the primary winding;
- and the primary rectifier configured to conduct a first current;
- a secondary rectifier coupled between the secondary winding and the output terminal, the secondary rectifier configured to rectify a secondary voltage across the secondary winding;
- a current detection circuit coupled to the secondary rectifier, the current detection circuit configured to generate a second current approximating the first current and based on the secondary voltage;
- and
- a control circuit configured to regulate the secondary rectifier at a frequency based on the second current.
Dependencies are inferred from the claim text.