SYNCHRONOUS RECTIFIER HAVING PRECISE ON/OFF SWITCHING TIME

• US 20080211473A1
• Filed: 12/20/2007
• Published: 09/04/2008
• Est. Priority Date: 12/22/2006
• Status: Active Grant

• Current Assignee: STMicroelectronics International N.V. (STMicroelectronics NV)
• Original Assignee: Stmicroelectronics Design And Application S.R.O. (STMicroelectronics NV)
• Inventors: Burda, David, Picq, Julien, Janik, Bohumil, Hukel, Miroslav, Tlasksl, Ondrej
• Granted Patent: US 8,013,586 B2
• Time in Patent Office: Days
• US Class Current: 323/283
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/38 Means for preventing simultaneous conduction of switches
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A synchronous rectifier, including an energy storage element having a terminal; a power supply input, connected to the terminal of the storage element in a first time interval; a reference line connected to the terminal of the storage element in a second time interval; and a zero comparator, coupled to the terminal of the storage element to detect a current flowing in the energy storage element and disconnect the terminal of the storage element from the reference line upon detecting a zero current, the zero comparator having an offset and a propagation time; the zero comparator further having an offset control input and an output. An offset regulating loop is coupled between the output of the zero comparator and the offset control input and regulates the offset of the zero comparator to compensate the propagation time.

Claims

1. A synchronous rectifier, comprising:

an energy storage element having a terminal;

a power supply input, connected to the terminal of the storage element in a first time interval;

a reference line connected to the terminal of the storage element in a second time interval;

a zero comparator, coupled to the terminal of the storage element to detect a current flowing in the energy storage element and to disconnect the terminal of the storage element from the reference line upon detecting a zero current, the zero comparator having an offset and a propagation time;

the zero comparator further having an offset control input and an output; and

an offset regulating loop coupled between the output of the zero comparator and the offset control input and regulating the offset of the zero comparator to compensate the propagation time.

2. The synchronous rectifier according to claim 1, further comprising a controlled switch coupled between the terminal of the storage element and the reference line, the controlled switch having a control input;

the zero comparator being connected to the control input of said controlled switch for switching off the controlled switch upon detecting the zero current.

3. The synchronous rectifier according to claim 2, wherein the offset regulating loop comprises a timing detector having a first input connected to the output of the zero detector, a second input connected the control input of the controlled switch, and an output, a charge pump circuit coupled between the output of the timing detector and the offset control input of the zero comparator and a filter connected to the offset control input of the zero comparator.

4. The synchronous rectifier according to claim 2, comprising a unidirectional freewheeling element, connected between the terminal of the storage element and the reference line.

5. The synchronous rectifier according to claim 2, wherein the controlled switch is an NMOS transistor.

6. The synchronous rectifier according to claim 1, forming a Switched Mode Power Supply circuit.

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

connecting a terminal of the energy storage element to a power supply input in a first time interval;

connecting the 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 zero comparator having an offset and a propagation time;

disconnecting the terminal of the energy storage element from the reference line upon detecting a zero current in the energy storage element;

regulating the offset of the zero comparator to compensate the propagation time.

8. The method of claim 7, wherein regulating comprises generating a compensating current correlated to a timing error between a zero current detecting time and an equilibrium time;

and filtering the compensating current.

9. The method of claim 7, wherein connecting the terminal of the energy storage element to a reference line comprises switching on a controlled switch;

detecting a current comprises detecting a voltage drop across the controlled switch; and

disconnecting the terminal comprises switching off the controlled switch and connecting the energy storage element to a freewheeling unipolar switch, thereby the voltage drop falls below the offset voltage.

10. The method of claim 9, wherein detecting a current comprises generating a zero signal having a first switching edge when the voltage drop first exceeds an offset voltage;

the step of disconnecting the terminal further comprises generating a second switching edge of the zero signal upon detecting the voltage drop falling below the offset voltage; and

the step of generating a compensating current comprises generating a third switching edge of the zero signal when the voltage drop again exceeds the offset voltage.

11. The method of claim 9, further comprising activating a first current source of a charge pump upon detecting the second switching edge;

deactivating the first current source and activating a second current source upon detecting the third switching edge;

deactivating the second current source after a fixed delay from activating the first current source.