ADAPTIVE ALGORITHM FOR CAMERA FLASH LED POWER CONTROL VS. BATTERY IMPEDANCE, STATE OF DISCHARGE (SOD), AGING, TEMPERATURE EFFECTS

• US 20090121644A1
• Filed: 10/29/2008
• Published: 05/14/2009
• Est. Priority Date: 11/14/2007
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments Deutschland Gesellschaft Mit Beschrã¤Nkter Haftung (Texas Instruments, Inc.)
• Inventors: Sandner, Harald, Vaucourt, Christophe, Schmeller, Hans, Kiml, Helmut, Rommel, Martin
• Granted Patent: US 7,990,074 B2
• Time in Patent Office: Days
• US Class Current: 315/241.P
• CPC Class Codes: H05B 45/00 Circuit arrangements for operating light-emitting diodes [LED]
• CPC Class Codes: H05B 45/30 Driver circuits
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/395 Linear regulators
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A method for driving a light-emitting semiconductor is provided. A supply voltage is converted into a secondary output voltage for supplying the light-emitting semiconductor with an output voltage. A level for the supply voltage at the beginning of a high current phase of the light-emitting semiconductor is sensed. A threshold voltage level for the supply voltage level is determined based on the sensed level. The high current phase with the light-emitting semiconductor is stated. The sensed level is continuously compared with the threshold voltage level, and an output current through the light-emitting semiconductor is controlled such that the sensed level does not drop below the threshold voltage level.

Claims

1. A method for driving a light-emitting semiconductor, the method comprising:

converting a supply voltage into a secondary output voltage for supplying the light-emitting semiconductor with an output voltage;

sensing a level for the supply voltage at the beginning of a high current phase of the light-emitting semiconductor;

determining a threshold voltage level for the supply voltage level based on the sensed level;

starting the high current phase with the light-emitting semiconductor;

continuously comparing the sensed level with the threshold voltage level; and

controlling an output current through the light-emitting semiconductor such that the sensed level does not drop below the threshold voltage level.

2. The method of claim 1, wherein the method further comprises the steps of:

increasing the output current through the light-emitting semiconductor during the high current phase; and

maintaining a magnitude of the output current once the sensed level is generally equal to the threshold voltage level.

3. The method of claim 1, wherein the step of determining further comprises the step of determining the threshold voltage level based on the sensed level and an allowable droop of the supply voltage at the end of the high current phase.

4. The method of claim 1, wherein the method further comprises the steps of:

generating a flash by the light-emitting semiconductor during the high current phase; and

determining the threshold voltage level within one microsecond from the beginning of the flash.

13. The apparatus of claim 1, wherein the apparatus further comprises the steps of:

means for increasing the output current through the light-emitting semiconductor during the high current phase; and

means for maintaining a magnitude of the output current once the sensed level is generally equal to the threshold voltage level.

14. The apparatus of claim 1, wherein the means for determining further comprises means for determining the threshold voltage level based on the sensed level and an allowable droop of the supply voltage at the end of the high current phase.

15. The apparatus of claim 1, wherein the apparatus further comprises:

means for generating a flash by the light-emitting semiconductor during the high current phase; and

means for determining the threshold voltage level within one microsecond from the beginning of the flash.

5. An apparatus comprising:

a plurality of light emitters;

a driver that receives a supply voltage and outputs a secondary voltage to a plurality of outputs paths, wherein each output path includes at least one light emitter;

a current regulator coupled to each output path, wherein the current regulator is adapted to determine a current through each output path; and

a controller that is coupled to the driver, the current regulator, and the output paths, wherein the controller includes;

a comparator that compares the supply voltage to a threshold voltage during a high current phase; and

control logic that determines the threshold voltage level at the beginning of the high current phase and that controls an output current through the light-emitter during the high current phase such that the supply voltage does not fall below the threshold voltage level.

6. The apparatus of claim 5, wherein the controller is adapted to continuously increase the output current during the high current phase and to maintain the output current at a generally constant level once the supply voltage is generally equal to the threshold voltage level.

7. The apparatus of claim 6, wherein the plurality of light emitters are LEDs.

8. The apparatus of claim 6, wherein a capacitor is coupled to each output path.

9. The apparatus of claim 6, wherein the controller further comprises:

a sensor that senses a current level for each output path and that compares each sensed current level to a reference level; and

adjusters that provide control signals to the current regulator.

10. The apparatus of claim 9, wherein the adjusters further comprise a plurality of digital to analog converters (DACs).

11. The apparatus of claim 7, wherein the sensor further comprises:

a multiplexer that receives a sense signal from each output path; and

a comparator that compares the output of the multiplexer to the reference level.

12. An apparatus for driving a light-emitting semiconductor, the method comprising:

means for converting a supply voltage into a secondary output voltage for supplying the light-emitting semiconductor with an output voltage;

means for sensing a level for the supply voltage at the beginning of a high current phase of the light-emitting semiconductor;

means for determining a threshold voltage level for the supply voltage level based on the sensed level;

means for starting the high current phase with the light-emitting semiconductor;

means for continuously comparing the sensed level with the threshold voltage level; and

means for controlling an output current through the light-emitting semiconductor such that the sensed level does not drop below the threshold voltage level.