Adaptive LCD power supply circuit

• US 6,873,322 B2
• Filed: 06/07/2002
• Issued: 03/29/2005
• Est. Priority Date: 06/07/2002
• Status: Expired due to Fees

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Hartular, Alexandru
• Primary Examiner(s): Mengistu, Amare
• Assistant Examiner(s): Sheng, Tom
• Application Number:
  US10/164,666
• Publication Number:
  US 20030227452A1
• Time in Patent Office: 1,026 Days
• Field of Search: 345211-213, 307/31
• US Class Current: 345/212
• CPC Class Codes: G09G 2330/02 Details of power systems and of start or stop of display operation
• CPC Class Codes: H02J 7/0063 with circuits adapted for supplying loads from the battery
• CPC Class Codes: H02J 7/007 Regulation of charging or discharging current or voltage
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]

Abstract

An adaptive LCD power supply circuit for adjusting at least one supply parameter in response to at least one load parameter of an associated load includes a feedback path configured to sense at least one load parameter and provide a control signal representative of at least one load parameter, and a regulating circuit configured to accept the control signal and regulate at least one supply parameter based on the control signal. The feedback path may include a first path to provide a first signal representative of a load condition of a first module, and a second path to provide a second signal representative of a load condition of a second load module, and a minimum decision circuit to output a third signal equal to the lesser of the first and second signals. An electronic device including an adaptive LCD power supply circuit is also provided.

Claims

1. A power supply circuit for adjusting at least one supply parameter in response to at least one load parameter of at least one associated load comprising:

a feedback path configured to sense said at least one load parameter and provide a control signal based on said at least one load parameter; and

a regulating circuit configured to accent said control signal and regulate said at least one supply parameter based on said control signal, wherein said feedback path comprises a first path providing a first signal representative of a first load condition of a first load module and a second path providing a second signal representative of a second load condition of a second load module, wherein said control signal is based on a comparison of said first signal and said second signal, and wherein said feedback path further comprises a minimum decision circuit configured to accept said first signal and said second signal and output a third signal equal to the lesser of said first signal and said second signal, wherein said control signal is based on said third signal.

2. The circuit of claim 1, wherein said feedback path further comprises an error amplifier configured to accept said third signal and a voltage reference signal from a voltage reference source and provide said control signal to said regulating circuit based on the difference between said third signal and said voltage reference signal.

3. The circuit of claim 1, wherein said first path comprises a light source and a current source, and wherein said first signal is representative of said at least one supply parameter output from said regulating circuit when said light source is disabled, and wherein said first signal is representative of a voltage drop across said current source when said light source is enabled.

4. The circuit of claim 3, wherein said first path further comprises a switch coupled to said light source and said current source, wherein said switch is configured to enable said light source when said switch is closed and disable said light source when said switch is open.

5. The circuit of claim 3, wherein said second path comprises a sensor configured to sense said second load condition of said second load module, and wherein said second signal is representative of a voltage drop across said sensor, said adaptive LCD power supply circuit configured to adjust said second signal such that said voltage drop across said sensor is equal to said reference voltage signal when said second signal is less than said first signal, and said adaptive LCD power supply circuit configured to adjust said first signal such that said voltage drop across said current source is equal to said reference voltage signal when said first signal is less than said second signal.

6. The circuit of claim 5, wherein said sensor is a transistor having a first electrode and a second electrode, and wherein said second signal is representative of a voltage across said first and second electrode.

7. The circuit of claim 6, wherein said transistor is a P-type MOSFET transistor, said first electrode is a source electrode and said second electrode is a drain electrode.

8. An electronic device comprising:

a liquid crystal display (LCD) panel circuit; and

an adaptive LCD power supply circuit for adjusting at least one supply parameter in response to at least one load parameter of at least one associated load, wherein one of said at least one associated load is an LCD panel circuit, said adaptive LCD power supply circuit comprising;

a feedback path configured to sense said at least one load parameter and provide a control signal based on said at least one load parameter; and

a regulating circuit configured to accept said control signal and regulate said at least one supply parameter based on said control signal, wherein said feedback path comprises a first path providing a first signal representative of first load condition of a first load module and a second path providing a second signal representative of a second load condition of said LCD panel circuit, wherein said control signal is based on a comparison of said first signal and said second signal, and wherein said feedback path further comprises a minimum decision circuit configured to accept said first signal and said second signal and output a third signal equal to the lesser of said first signal and said second signal, wherein said control signal is based on said third signal.

9. The device of claim 8, wherein said first path comprises a light source and a current source, and wherein said first signal is representative of said at least one supply parameter output from said regulating circuit when said light source is disabled, and wherein said first signal is representative of a voltage drop across said current source when said light source is enabled.

10. The device of claim 9, wherein said first path further comprises a switch coupled to said light source and said current source, wherein said switch is configured to enable said light source when said switch is closed and disable said light source when said switch is open.

11. The device of claim 9, wherein said second path comprises a sensor configured to sense said second load condition of said LCD panel circuit, and wherein said second signal is representative of a voltage drop across said sensor, said adaptive LCD power supply circuit adjusting said second signal such that said voltage drop across said sensor is equal to said reference voltage signal when said second signal is less than said first signal, and said adaptive LCD power supply circuit adjusting said first signal such that said voltage drop across said current source is equal to said reference voltage signal when said first signal is less than said second signal.

12. The device of claim 11, wherein said sensor is a transistor having a first electrode and a second electrode, and wherein said second signal is representative of a voltage across said first and second electrode.

13. The device of claim 12, wherein said transistor is a P-type MOSFET transistor, said first electrode is a source electrode and said second electrode is a drain electrode.

14. An adaptive liquid crystal display (LCD) power supply circuit for adjusting at least one supply parameter in response to a load condition from one of a plurality of load modules, said adaptive LCD power supply circuit comprising:

a first path providing a first signal representative of a load condition of a first load module;

a second path providing a second signal representative of a load condition of a second load module;

a minimum decision circuit configured to accept said first signal and said second signal and output a third signal equal to the lesser of said first signal and said second signal; and

a regulating circuit configured to accept a control signal based on said third signal and regulate said at least one supply parameter based on said control signal.

15. The circuit of claim 14, wherein said at least one supply parameter is DC voltage and said regulating circuit is a DC-DC converter.

16. The circuit of claim 14, further comprising an error amplifier configured to accept said third signal and a voltage reference signal from a voltage reference source, wherein said error amplifier is further configured to provide said control signal based on the difference between said third signal and said voltage reference signal.

17. The circuit of claim 14, wherein said first load module is a light source providing backlight for an LCD and said second load module is an LCD panel circuit.

18. The circuit of claim 17, wherein said first path comprises said light source, a current source configured to provide current to said light source, and a switch coupled between said light source and said current source, wherein the position of the switch enables current from said current source to enable or disable said light source.

19. The circuit of claim 18, wherein said first signal is representative of said at least one supply parameter output from said regulating circuit when said switch is open and said light source is disabled, and wherein said first signal is representative of a voltage drop across said current source when said switch is closed and said light source is enabled.

20. The circuit of claim 18, wherein said second path comprises a sensor configured to sense said load condition of said LCD panel circuit, and wherein said second signal is representative of a voltage drop across said sensor, said adaptive LCD power supply circuit is configured to adjust said second signal such that said voltage drop across sensor is equal to said reference voltage signal when said second signal is less than said first signal, and said adaptive LCD power supply circuit is configured to adjust said first signal such that said voltage drop across said current source is equal to said reference voltage signal when said first signal is less than said second signal.

21. The circuit of claim 20, wherein said sensor is a transistor having a first electrode and a second electrode wherein a voltage across said first and second electrode is representative of said load condition of said second load module.

22. The circuit of claim 21, wherein said transistor is a P-type MOSFET transistor, said first electrode is a source electrode, and said second electrode is a drain electrode.

23. The circuit of claim 14, wherein said second path comprises a sensor configured to sense said load condition of said second load module.

24. A method of adjusting at least one supply parameter comprising the steps of:

sensing at least one load parameter from a first load module and providing a first signal representative of said at least one load parameter from said first load module;

sensing at least one load parameter from a second load module and providing a second signal representative of said at least one load parameter from said second load module;

comparing said first signal and said second signal and providing a third signal equal to the lesser of said first signal and said second signal; and

adjusting said at least one supply parameter based on said third signal.

25. The method of claim 24, further comprising the steps of:

providing a reference signal; and

comparing said reference signal with said third signal and providing a control signal for adjusting said at least one supply parameter based on said control signal until said third signal equals said reference signal.

26. The method of claim 25, further comprising the step of:

increasing said at least one supply parameter when said third signal is less than said reference signal.

27. The method of claim 25, further comprising the step of:

decreasing said at least one supply parameter when said third signal is greater than said reference signal.