Adaptive rectifier Architecture and method for switching regulators

• US 20080298106A1
• Filed: 05/16/2008
• Published: 12/04/2008
• Est. Priority Date: 05/30/2007
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Tateishi, Tetsuo
• Granted Patent: US 8,278,889 B2
• Time in Patent Office: Days
• US Class Current: 363/127
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/0012 Control circuits using digital or numerical techniques in DC/DC converters H02M3/157, H02M3/33515; in DC-AC converters H02M7/53873
• 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

An adjustable compensation offset voltage is applied to a comparator to vary turn-off timing of a synchronous rectifier. A comparator output indicates when current through an inductor coupled to the synchronous rectifier should be approaching zero. If the synchronous rectifier is turned off before the current through the inductor reaches zero, the compensation offset voltage is adjusted to delay the synchronous rectifier turn-off for the next switching cycle. If the synchronous rectifier is turned off after the current through the inductor reaches zero, the compensation offset voltage is adjusted to advance the synchronous rectifier turn-off for the next switching cycle. An up/down counter, in conjunction with a digital to analog converter, may be used to provide the adjustment to the compensation offset voltage. The adjustable compensation offset voltage improves the accuracy of synchronous rectifier turn-off in relation to a zero inductor current, thereby improving power converter efficiency.

Claims

1. A control system for turning off a synchronous rectifier in an inductor-based power converter, comprising:

a comparator having an input coupled to an inductor in the power converter to obtain an indication of inductor current, and having an output coupled to the synchronous rectifier to switch off the synchronous rectifier;

an adjustable compensation offset voltage source coupled to an input of the comparator; and

a compensation offset voltage source controller coupled to the output of the comparator and to the compensation offset voltage source and being operable to adjust an output value of the compensation offset voltage source in accordance with a timing relationship between a transition of the output of the comparator and the indication of inductor current being a predetermined value.

2. The system according to claim 1, further comprising an up/down counter provided as the compensation offset voltage source.

3. The system according to claim 1, wherein the predetermined value represents an indication of zero inductor current.

4. The system according to claim 1, wherein the predetermined value is a positive voltage value.

5. The system according to claim 1, further comprising a MOSFET as the synchronous rectifier.

6. The system according to claim 1, further comprising a delay element coupled to the synchronous rectifier and the compensation offset voltage source to provide a delay in obtaining the indication of inductor current.

7. The system according to claim 1, further comprising a digital to analog converter (DAC) coupled to the compensation offset voltage source controller and the compensation offset voltage source to convert a control signal from the compensation offset voltage source controller to the compensation offset voltage source.

8. The system according to claim 1, wherein the compensation offset voltage source controller is further operable to adjust the compensation offset voltage source to have a greater output value if the transition of the output comparator is subsequent to the indication of inductor current being a predetermined value, and is further operable to adjust the output value of the compensation offset voltage source to have a lesser value if the transition of the output of the comparator is prior to the indication of the inductor current being a predetermined value.

9. The system according to claim 1, further comprising a sense resistor coupled to the inputs of the comparator.

10. The system according to claim 1, wherein the inputs to the comparator are arranged to be across the synchronous rectifier.

11. A method for controlling a synchronous rectifier in an inductor-based power converter, the method comprising:

turning the synchronous rectifier off;

obtaining an indication of a value of current in an inductor in the power converter;

comparing the indication to a compensation offset voltage; and

modifying the compensation offset voltage in accordance with a synchronous rectifier turn-off timing in relation to a predetermined value of the indication.

12. The system according to claim 11, further comprising modifying the compensation offset voltage using an up/down counter.

13. The system according to claim 11, wherein the predetermined value represents zero inductor current.

14. The system according to claim 11, wherein the predetermined value is a positive voltage value.

15. The system according to claim 11, further comprising implementing the synchronous rectifier as a MOSFET.

16. The system according to claim 11, further comprising delaying the obtaining of the indication.

17. The system according to claim 12, further comprising converting an output of the up/down counter to an analog signal to provide the compensation offset voltage.

18. The system according to claim 11, further comprising adjusting the compensation offset voltage to have a greater output value if the synchronous rectifier turn-off is subsequent to the indication of the value of current in the inductor becoming the predetermined value, and adjusting the compensation offset voltage to have a lesser value if the synchronous rectifier turn-off is prior to the value of current in the inductor becoming the predetermined value.

19. The system according to claim 11, further comprising using a sense resistor for the obtaining the indication of the value of current in the inductor.

20. The system according to claim 11, further comprising using the synchronous rectifier for the obtaining the indication of the value of current in the inductor.