CIRCUITS AND METHODS FOR DRIVING LIGHT SOURCES

• US 20110133662A1
• Filed: 04/16/2010
• Published: 06/09/2011
• Est. Priority Date: 03/04/2010
• Status: Active Grant

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: YAN, Tiesheng, LI, Youling, LIN, Feng, SU, Xinhe, KUO, Ching-Chuan
• Granted Patent: US 8,339,063 B2
• Time in Patent Office: Days
• US Class Current: 315/224
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 47/10 Controlling the light source

Abstract

A driving circuit includes a first inductor coupled in series with a light source for providing power to the light source. A controller coupled to the first inductor can control a switch coupled to the first inductor, thereby controlling a current flowing through the first inductor. A current sensor coupled to the first inductor can provide a first signal indicative of the current flowing through the first inductor, regardless of whether the switch is on or off. The switch is controlled according to the first signal. A second inductor magnetically coupled to the first inductor is also electrically coupled to the first inductor via a common node between the switch and the first inductor for providing a reference ground for the controller. The reference ground is different from the ground of the driving circuit.

Claims

1. A driving circuit, comprising:

a first inductor coupled in series with a light emitting diode (LED) light source and for providing power to said LED light source;

a controller operable for controlling a switch coupled to said first inductor, thereby controlling a current flowing through said first inductor;

a current sensor coupled to said first inductor and operable for providing a first signal indicative of said current flowing through said first inductor, regardless of whether said switch is on or off, wherein said switch is controlled according to said first signal; and

a second inductor magnetically and electrically coupled to said first inductor and operable for sensing an electrical condition of said first inductor, wherein said first inductor and said second inductor are electrically coupled to a common node between said switch and said first inductor, wherein said common node provides a reference ground for said controller, and wherein said reference ground is different from the ground of said driving circuit.

2. The driving circuit of claim 1, further comprising:

a filter coupled to said current sensor and operable for providing a second signal indicative of an average current flowing through said first inductor; and

an error amplifier operable for generating an error signal based on said second signal and a reference signal indicative of a target current level,

wherein said switch is turned off if a voltage of said first signal increases above a voltage of said error signal.

3. The driving circuit of claim 2, wherein said error amplifier is operable for generating said error signal to adjust a current flowing through said LED light source to said target current level.

4. The driving circuit of claim 2, wherein said controller is operable for generating a pulse-width modulation signal to control said switch, and wherein a duty cycle of said pulse-width modulation signal is determined by said error signal.

5. The driving circuit of claim 1, wherein said controller has a ground terminal coupled to said common node, and wherein a conductance status of said switch is determined based on a difference between a gate voltage of said switch and a voltage at said common node.

6. The driving circuit of claim 1, wherein said switch is turned on if said current flowing through said first inductor decreases to a predetermined current level.

7. The driving circuit of claim 1, further comprising:

a filter coupled to said current sensor and operable for providing a second signal indicative of an average current flowing through said first inductor;

a signal generator operable for generating a sawtooth signal; and

an error amplifier operable for generating an error signal based on said second signal and a reference signal indicative of a target current level,

wherein said switch is turned off if a voltage of said sawtooth signal increases to a voltage of said error signal.

8. The driving circuit of claim 1, further comprising:

a reset signal generator operable for generating a reset signal,

wherein said switch is turned on in response to said reset signal.

9. The driving circuit of claim 8, wherein said reset signal comprises a pulse signal having a constant frequency.

10. The driving circuit of claim 8, wherein said reset signal comprises a pulse signal configured in such a way that a time period during which said switch is off is constant.

11. A controller for controlling power to a light emitting diode (LED) light source, said controller comprising:

a first sensing pin operable for sensing an instant current flowing through an energy storage element;

a second sensing pin operable for sensing an average current flowing through said energy storage element;

a third sensing pin operable for detecting whether said instant current decreases to a predetermined current level; and

a driving pin operable for providing a driving signal to a switch to control an average current flowing through said LED light source to a target current level, wherein said driving signal is generated based on signals through said first sensing pin, said second sensing pin, and said third sensing pin.

12. The controller of claim 11, further comprising:

an error amplifier operable for generating an error signal based on said target current level and said average current flowing through said energy storage element.

13. The controller of claim 12, further comprising:

a comparator coupled to said error amplifier and operable for comparing said error signal with a sense signal indicative of said instant current.

14. The controller of claim 13, further comprising:

a pulse-width modulation signal generator coupled to said comparator and operable for generating a pulse-width modulation signal based on an output of said comparator and a detection signal indicative of whether said instant current decreases to said predetermined current level.

15. The controller of claim 12, further comprising:

a comparator coupled to said error amplifier and operable for comparing said error signal with a sawtooth signal.

16. The controller of claim 15, further comprising:

a pulse-width modulation signal generator coupled to said comparator and operable for generating a pulse-width modulation signal based on an output of said comparator and a reset signal.

17. The controller of claim 16, wherein said reset signal comprises a pulse signal having a constant frequency.

18. The controller of claim 16, wherein said pulse-width modulation signal has a first state and a second state, and wherein said reset signal comprises a pulse signal configured in such a way that a time period during which said pulse-width modulation signal is in said second state is constant.