SWEEPING FREQUENCY LLC RESONANT POWER REGULATOR

• US 20110305044A1
• Filed: 01/07/2009
• Published: 12/15/2011
• Est. Priority Date: 01/07/2009
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Huang, Fuen
• Granted Patent: US 8,717,782 B2
• Time in Patent Office: Days
• US Class Current: 363/21.02
• CPC Class Codes: H02M 7/53806 in a push-pull configuration of the parallel type
• 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 LLC resonant power regulator system (10) includes a transformer (22) comprising a primary inductor (20) and a secondary inductor (26) and an input resonant tank (18) comprising an input resonant capacitor, an input leakage inductor, and the primary inductor (20) connected in series. The system also includes an input stage (14) comprising a plurality of switches (16) that are controlled in response to a respective plurality of switching signals sweeping frequency to supply an input resonant current to the input resonant tank (18). Each of the respective plurality of switching signals can have a fixed duty cycle and a sweeping frequency. The system (10) further comprises an output resonant tank (24) comprising an output resonant capacitor, an output leakage inductor, and the secondary inductor (26) connected in series. The output resonant tank (24) can be configured to generate an oscillating output resonant current at an output.

Claims

1. An LLC resonant power regulator system comprising:

a transformer comprising a primary inductor and a secondary inductor;

an input resonant tank comprising an input resonant capacitor, an input leakage inductor, and the primary inductor connected in series;

an input stage comprising a plurality of switches that are controlled in response to a respective plurality of switching signals sweeping frequency to supply an input resonant current to the input resonant tank, each of the respective plurality of switching signals having a fixed duty cycle and a sweeping frequency; and

an output resonant tank comprising an output resonant capacitor, an output leakage inductor, and the secondary inductor connected in series, the output resonant tank being configured to generate an oscillating output resonant current at an output.

2. The system of claim 1, further comprising a feedback controller configured to provide a feedback signal depending on a difference between the output resonant current and a predetermined reference.

3. The system of claim 2, further comprising a switch control stage configured to provide the plurality of switching signals and to regulate the sweeping frequency of the plurality of switching signals within a sweeping frequency range in response to the feedback signal, the sweeping frequency range being between a first frequency and a second frequency that is greater than the first frequency.

4. The system of claim 3, wherein the input resonant tank has a first resonant frequency that is set according to the input resonant capacitor and the input leakage inductor and has a second resonant frequency that is set according to the input resonant capacitor, the input leakage inductor, and the primary inductor, and

wherein the switch control stage is further configured to set the first frequency of the sweeping frequency range to be greater than at least one of the first resonant frequency and the second resonant frequency to maintain zero voltage switching (ZVS) control of the plurality of switches.

5. The system of claim 3, wherein the switch control stage is configured to set the fixed duty-cycle for each of the plurality of switching signals at approximately 50%.

6. The system of claim 1, wherein the plurality of switches comprises a first switch and a second switch that are arranged as a half-bridge between an input voltage and a second voltage, the half-bridge comprising an interconnecting node that is coupled to the input resonant tank.

7. The system of claim 6, wherein the first switch is controlled by a first switching signal and the second switch is controlled by a second switching signal, the first and second switching signals each having an approximately 50% duty-cycle and being approximately 180°

out-of-phase relative to each other.

8. The system of claim 1, further comprising a plurality of output stages, each of the plurality of output stages comprising resonant circuitry that includes an output stage resonant tank, the sweeping frequency being controlled to regulate the output resonant current in each respective output stage resonant tank.

9. The system of claim 8, wherein the transformer is configured to generate an intermediate current at the secondary inductor thereof in response to the input resonant current through the primary inductor thereof, and wherein each of the plurality of output stages further comprises:

an output stage transformer comprising an output primary inductor inductively coupled with an output secondary inductor, the output primary inductor conducting the intermediate current therethrough to induce a corresponding output stage resonant current through the output secondary inductor; and

the resonant circuitry comprising the output secondary inductor of the output stage transformer, the output leakage inductor of the output stage transformer, and at least one output resonant capacitor connected in series with a respective load, the corresponding output resonant current oscillating through the resonant circuitry to the respective load connected in series with the at least one resonant capacitor.

10. The system of claim 1, wherein the input resonant tank further comprises at least one additional inductor connected in series with the input resonant capacitor, the input leakage inductor, and the primary inductor.

11. The system of claim 1, further comprising a cold cathode fluorescent lamp (CCFL) connected at the output of the output resonant tank.

12. A method for providing AC power via an LLC resonant power regulator, the method comprising:

generating a plurality of switching signals having a substantially fixed 50% duty-cycle and a sweeping frequency;

controlling a plurality of switches in response to the respective plurality of switching signals to provide an input resonant current to an input resonant tank, the input resonant tank comprising an input resonant capacitor, an input leakage inductor, and a primary inductor of a transformer;

inducing an output resonant current through a secondary inductor of the transformer in response to the input resonant current, the output resonant current resonating through an output resonant tank that includes the secondary inductor of the transformer; and

conducting the output resonant current as an AC current through a load, the load being coupled in series with the output resonant tank.

13. The method of claim 12, further comprising:

sensing a magnitude of the output resonant current to provide a sensor signal indicative of a magnitude of the output resonant current;

comparing the sensor signal with a predetermined reference to provide a feedback signal; and

regulating a frequency of the plurality of switching signals to within a sweeping frequency range associated with the sweeping frequency in response to the feedback signal.

14. The method of claim 13, wherein regulating the frequency comprises:

setting the sweeping frequency range to be between a first frequency and a second frequency that is greater than the first frequency; and

setting the first frequency to be greater than at least one of a first resonant frequency that is based on the input resonant capacitor and the input leakage inductor and a second resonant frequency that is based on the input resonant capacitor, the input leakage inductor, and the primary inductor to deactivate the plurality of switches in a zero voltage switching (ZVS) manner.

15. The method of claim 12, wherein generating the plurality of switching signals comprises generating a first switching signal and a second switching signal, the first and second switching signals being approximately 180°

out-of-phase relative to each other, and wherein controlling the plurality of switches comprises;

controlling a first switch in response to the first switching signal; and

controlling a second switch in response to the second switching signal, the first and second switch being configured as a half-bridge between an input voltage and a second voltage, the half-bridge having an interconnecting node that is coupled to provide the input resonant current to the input resonant tank.

16. The method of claim 12, wherein inducing the output resonant current further comprises inducing an output resonant current through an output secondary inductor of each of a plurality of output stage transformers in response to the input resonant current, the output resonant current resonating through each of a respective plurality of output resonant circuits, each of which includes the respective output secondary inductor.

17. The method of claim 16, wherein conducting the output resonant current comprises conducting the output resonant current as an AC current through each of a plurality of loads connected with each of the plurality output resonant circuits, each of the plurality of loads being coupled in series with a respective resonant capacitor that is coupled with the respective output secondary inductor of a respective one of the plurality of output resonant circuits.

18. The method of claim 16, wherein inducing the output resonant current further comprises:

generating an intermediate current at the secondary inductor of the transformer in response to the input resonant current;

providing the intermediate current to each of a plurality of output primary inductors associated with the respective plurality of output stage transformers; and

inducing the output resonant current through the output secondary inductor of each of the plurality of output stage transformers in response to the intermediate current.

19. An LLC resonant power regulator system comprising:

means for generating a plurality of switching signals having a substantially fixed duty-cycle and a sweeping frequency having a predefined range;

means for alternately coupling a control node between an input voltage and a reference voltage in response to the plurality of switching signals;

means for resonating an input resonant current in response to voltage changes at the control node, the means for resonating having a first resonant frequency and a second resonant frequency that are defined by circuit component characteristics of the means for resonating;

means for inducing an output resonant current in an output stage in response to the input resonant current, the output resonant current oscillating through a load;

means for sensing a magnitude of the output resonant current; and

means for regulating a frequency of the plurality of switching signals to within the sweeping frequency predefined range based on the magnitude of the output resonant current relative to a predetermined reference magnitude.

20. The system of claim 19, wherein the means for inducing an output resonant current comprises plural means for inducing, each of the plural means for inducing causing a respective plurality of output resonant currents to be induced in a respective plurality of output stages, the plurality of output resonant currents oscillating through at least one load that is connected with each of the plurality of output stages.