Resonant switching converter having operating modes above and below resonant frequency

• US 7,660,133 B1
• Filed: 11/04/2008
• Issued: 02/09/2010
• Est. Priority Date: 11/04/2008
• Status: Active Grant

• Current Assignee: Champion Microelectronic Corporation
• Original Assignee: Champion Microelectronic Corporation
• Inventors: Hwang, Jeffrey, Chee, Alland
• Primary Examiner(s): Riley; Shawn
• Application Number:
  US12/290,853
• Time in Patent Office: 462 Days
• Field of Search: 363/16, 363/131, 363/15, 363/13
• US Class Current: 363/16
• CPC Class Codes: H02M 1/0058 by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero using an auxiliary actively switched resonant commutation circuit connected to an intermediate DC voltage or between two push-pull branches of an inverter bridge H02M7/4811; in resonant inverters H02M7/4815; in inverters operating from a resonant DC source H02M7/4826
• CPC Class Codes: H02M 3/33592 having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
• 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 resonant switching converter comprises a resonant tank having a resonant frequency; a synchronous rectifier coupled to the resonant tank, the synchronous rectifier drawing power from the resonant tank for forming an output voltage; and a controller coupled to the synchronous rectifier for controlling switching of the synchronous rectifier using frequency modulation. The controller operates in a first mode in which the switching of the synchronous rectifier is performed above the resonant frequency of the resonant tank. The first mode employs a duty cycle for the synchronous rectifier. In addition, the controller operates in a second mode in which the switching of the synchronous rectifier is performed below the resonant frequency and the duty cycle of the synchronous rectifier in the second mode is reduced from that of the first mode.

Claims

1. A resonant switching converter comprising:

a resonant tank having a resonant frequency;

a synchronous rectifier coupled to the resonant tank, the synchronous rectifier drawing power from the resonant tank for forming an output voltage; and

a controller coupled to the synchronous rectifier for controlling switching of the synchronous rectifier using frequency modulation, wherein the controller operates in a first mode in which the switching of the synchronous rectifier is performed above the resonant frequency of the resonant tank, the first mode employing a duty cycle for the synchronous rectifier, and wherein the controller operates in a second mode in which the switching of the synchronous rectifier is performed below the resonant frequency and the duty cycle of the synchronous rectifier in the second mode is reduced from that of the first mode.

2. The resonant switching converter according to claim 1, further comprising a switching inverter coupled to the resonant tank for charging the resonant tank with energy wherein the controller controls switching of the switching inverter.

3. The resonant switching converter according to claim 2, wherein switching of the switching inverter is performed at the same frequency as the switching of the synchronous rectifier using frequency modulation and wherein a duty cycle for the switching inverter is the same in both the first mode and the second mode.

4. The resonant switching converter according to claim 3, wherein the duty cycle for the switching inverter is fifty percent in both the first mode and the second mode and wherein the duty cycle for the synchronous rectifier in the first mode is fifty percent.

5. The resonant switching converter according to claim 2, wherein the controller operates in a third mode in which the duty cycle of the synchronous rectifier and the duty cycle of the synchronous rectifier are reduced from that of the first mode and wherein the third mode is entered in response to a light load condition.

6. The resonant switching converter according to claim 5, wherein the light load condition is indicated when the switching frequency exceeds a specified level.

7. The resonant switching converter according to claim 2, wherein upon start-up of the resonant switching converter operation of the switching inverter is commenced immediately and operation of the switching rectifier is commenced only after a delay.

8. The resonant switching converter according to claim 1, wherein the resonant tank comprises an inductor and a capacitor coupled in series to form a series resonant converter.

9. The resonant switching converter according to claim 1, wherein the on-time for switching of the synchronous rectifier in the second mode is constant.

10. The resonant switching converter according to claim 9, wherein the on-time for switching of the synchronous rectifier in the second mode is equivalent to half of the period of the resonant frequency.

11. The resonant switching converter according to claim 1, wherein the on-time for switching of the synchronous rectifier in the second mode is less than half of the period of the resonant frequency.

12. The resonant switching converter according to claim 1, wherein a frequency of switching in the synchronous rectifier is modulated according to a monitored level of the output voltage, thereby, regulating the output voltage in a feedback loop.

13. The resonant switching converter according to claim 1, wherein the duty cycle of the synchronous rectifier is controlled by monitoring current levels in switches of the synchronous rectifier.

14. The resonant switching converter according to claim 1, further comprising a transformer having a primary winding and a secondary winding, the primary winding being coupled to the resonant tank and the secondary winding being coupled to the synchronous rectifier.

15. The resonant switching converter according to claim 1 wherein an output current is monitored and the controller controls switching to reduce the output current when it exceeds a specified level, wherein the specified level is set to a first level upon start-up of the resonant switching converter and, after a delay, the specified level is set to a second level, lower than the first level.

16. The resonant switching converter according to claim 1 wherein switching is controlled in a feedback loop based upon a level of an error signal, the error signal being representative of a difference between the output voltage and a desired level of the output voltage.

17. The resonant switching converter according to claim 16, wherein upon start-up of the resonant switching converter, the error signal is first set to a specified level and then allowed to assume a level that is representative of the difference between the output voltage and the desired level of the output voltage.

18. A controller for a resonant switching converter comprising;

means for generating switching signals for operating a synchronous rectifier to draw power from a resonant tank for forming an output voltage; and

means for controlling the switching signals using frequency modulation, wherein the means for controlling operates the synchronous rectifier in a first mode in which the switching of the synchronous rectifier is performed above the resonant frequency of the resonant tank, the first mode employing a duty cycle for the synchronous rectifier, and wherein the means for controlling operates the synchronous rectifier in a second mode in which the switching of the synchronous rectifier is performed below the resonant frequency and wherein the duty cycle of the synchronous rectifier in the second mode is reduced from that of the first mode.

19. The resonant switching converter according to claim 18, wherein the means for generating further generates switching signals for operating a switching inverter coupled to the resonant tank for charging the resonant tank with energy.

20. A method of controlling a resonant switching converter comprising:

operating a synchronous rectifier to draw power from a resonant tank for forming an output voltage; and

controlling switching of the synchronous rectifier using frequency modulation, wherein said controlling comprises operating the synchronous rectifier in a first mode in which the switching of the synchronous rectifier is performed above the resonant frequency of the resonant tank, the first mode employing a duty cycle for the synchronous rectifier, and wherein said controlling comprises operating the synchronous rectifier in a second mode in which the switching of the synchronous rectifier is performed below the resonant frequency and wherein the duty cycle of the synchronous rectifier in the second mode is reduced from that of the first mode.