Power supply apparatus and method for a backlight system

1. A power supply system, comprising: a transformer having a primary winding on its primary side for coupling to a power source and one or more secondary windings on its secondary side; a first control circuit disposed on the primary side of the transformer for controlling a current flow in the primary winding, the first controller including a pulse-width modulation (PWM) control circuit configured to operate with 50% duty cycle at a frequency for maximum voltage gain for a given load condition; and a second control circuit disposed on the secondary side of the transformer, the second control circuit being configured to provide a regulated output voltage; wherein the first control circuit is configured to generate a control signal for controlling the current flow in the primary winding without using a feedback control signal from the secondary side of the transformer.

2. The power supply system of claim 1 , wherein the first control circuit comprises an LLC resonant circuit.

3. The power supply system of claim 2 , wherein the LLC resonant circuit comprises a leakage inductance provided by the transformer.

4. The power supply system of claim 1 , wherein the first control circuit comprises an asymmetric half bridge circuit.

5. The power supply system of claim 1 , wherein the first control circuit comprises a second transformer coupled between a pulse signal generator and two transistors.

6. The power supply system of claim 1 , wherein the first control circuit comprises an integrated circuit that is configured to provide a pulsed control signal.

7. A backlight system for providing backlight to a display device, the backlight system comprising:

a transformer having a primary winding on its primary side for coupling to a power source and one or more secondary windings on its secondary side;

a first control circuit disposed on the primary side of the transformer for controlling a current flow in the primary winding; and

a second control circuit disposed on the secondary side of the transformer, the second control circuit being configured to provide a regulated output voltage; and

a backlight apparatus that includes one or more light devices;

wherein the first control circuit is configured to generate a control signal for controlling the current flow in the primary winding without using a feedback control signal from the secondary side of the transformer;

wherein the second control circuit comprises a pulse width modulated (PWM) control circuit.

8. The backlight system of claim 7 , wherein the backlight apparatus comprises one or more light emitting diode (LED) devices.

9. The backlight system of claim 7 , wherein the first control circuit comprises an LLC resonant circuit.

10. The backlight system of claim 9 , wherein the LLC resonant circuit comprises a resonant inductor and a resonant capacitor.

11. The backlight system of claim 7 , wherein the second control circuit is configured to receive a feedback signal from the backlight apparatus.

12. The backlight system of claim 7 , wherein the second control circuit comprises a voltage boost circuit.

13. The backlight system of claim 7 , wherein the first control circuit comprises a first power switch and a second power switch having substantially the same duty cycle.

14. The backlight system of claim 7 , wherein the first control circuit comprises an asymmetric half bridge circuit.

15. The backlight system of claim 7 , wherein the first control circuit comprises a first power switch and a second power switch having complementary duty cycles, D and 1-D, respectively.

16. A power supply system, comprising: a transformer having a primary winding on its primary side for coupling to a power source and one or more secondary windings on its secondary side; a first control circuit disposed on the primary side of the transformer for controlling a current flow in the primary winding, the first controller including an LLC resonant circuit, the first controller including a pulse width modulated (PWM) control circuit configured to operate at a frequency for a peak voltage gain for a target load condition; and a second control circuit disposed on the secondary side of the transformer, the second control circuit being configured to provide a regulated output voltage; wherein the first control circuit is configured to generate a control signal for controlling the current flow in the primary winding without using a feedback control signal from the secondary side of the transformer.

17. The power supply system of claim 16 , wherein the first controller further comprises an LLC resonant circuit including a resonant inductor and a resonant capacitor.

18. The power supply system of claim 17 , wherein the first controller includes a pulse width modulated (PWM) control circuit configured to operate at a frequency that is lower than a first frequency fr 1 and higher than a second frequency fr 2 , wherein

f

r

⁢

⁢

1

=

1

2

⁢

π

·

L

r

·

C

r

⁢

⁢

and

f

r

⁢

⁢

2

=

1

2

⁢

π

·

(

L

r

+

L

m

)

·

C

r

wherein Cr is the capacitance of the resonant capacitor, Lr is the inductance of the resonant inductor, and Lm is a magnetizing inductance Lm of the transformer.

19. The power supply system of claim 16 , wherein the pulse width modulated (PWM) control circuit is configured to operate at a substantially 50% duty cycle.

20. The power supply system of claim 16 , wherein the second control circuit comprises a pulse width modulated (PWM) control circuit.