Highly efficient driving of photoflash diodes using low and fixed voltage drop-out current sink

1. A driving circuit comprising:

a first diode;

a first current regulator coupled to said first diode operable for controlling a current through said first diode and for providing a voltage signal;

a feedback circuit operable for receiving a first feedback signal indicative of an electrical condition of said first current regulator;

a DC-DC converter coupled to an external power source and said feedback circuit for powering said first diode so as to control said electrical condition of said first current regulator to a predetermined; and

a bias controller operable for receiving a specified current signal and said voltage signal and for driving said first current regulator according to said specified current signal and said voltage signal.

2. The driving circuit of claim 1 , wherein said first diode comprises a photoflash diode.

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

an error amplifier for comparing said first feedback signal and a predetermined signal indicative of said predetermined value so as to determine power supplied to said first diode.

4. The driving circuit of claim 3 , wherein said error amplifier comprises:

a comparator for comparing said first feedback signal and said predetermined signal and for outputting an amplified error signal to determine said power supplied to said first diode;

a switch network for disenabling said comparator and for outputting a fixed signal when said amplified error signal is larger than said fixed signal.

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

a second diode;

a second current regulator coupled to said second diode for controlling a current through said second diode; and

a selecting circuit coupled to said first current regulator and said second current regulator and for generating a second feedback signal selectively indicative of said electrical condition of said first current regulator and an electrical condition of said second current regulator.

6. The driving circuit of claim 5 , wherein said second feedback signal is indicative of a lower voltage from voltages at said first current regulator and said second current regulator.

7. The driving circuit of claim 1 , wherein said current regulator is comprises a current sink.

8. The driving circuit of claim 1 , wherein said bias controller further comprises:

a first MOSFET, wherein a gate of said first MOSFET is coupled to a gate of said current regulator and is driven in a linear region; and

a second MOSFET, wherein a gate of said second MOSFET is coupled to said first feedback signal.

9. A method for driving a diode comprising:

controlling a current through said diode by a current regulator;

providing a voltage signal from said current regulator to a bias controller;

providing a specified current signal to said bias controller;

driving said current regulator by said bias controller according to said voltage signal from said current regulator and according to said specified current signal;

generating a feedback signal indicative of an electrical condition of said current regulator; and

supplying power to said diode according to said feedback signal so as to force said electrical condition of said current regulator to a predetermined value.

10. The method of claim 9 , wherein said diode comprises a photoflash diode.

11. The method of claim 9 , further comprising:

comparing said feedback signal and a predetermined signal indicative of said predetermined value so as to determine said power supplied to said diode.

12. A method for driving a plurality of diodes comprising:

controlling a plurality of currents through said diodes by a plurality of current regulators, respectively;

providing a plurality of voltage signals from said plurality of current regulators to a bias controller;

providing a plurality of specified current signals to said bias controller;

driving said plurality of current regulators by said bias controller according to said plurality of voltage signals from said current regulators and according to said plurality of specified current signals;

generating a feedback signal indicative of a plurality of electrical conditions of said current regulators; and

supplying power to said plurality of diodes according to said feedback signal so as to force said plurality of electrical conditions of said plurality of current regulators to a predetermined value.

13. The method of claim 12 , wherein said diode comprises a photoflash diode.

14. The method of claim 12 , wherein generating a feedback signal further comprises:

selecting a lowest voltage signal from said plurality of voltage signals generated at said current regulators; and

generating said feedback signal indicative of said lowest voltage signal.

15. The method of claim 14 , wherein said current regulator comprises a current sink.

16. The method of claim 12 , further comprising:

comparing said feedback signal and a predetermined signal indicative of said predetermined value so as to determine said power supplied to said plurality of diodes.

17. A driving circuit for driving a plurality of diodes comprising:

a plurality of current regulators coupled to said plurality of diodes for controlling a plurality of currents through said plurality of diodes, respectively;

a selecting circuit coupled to said plurality of current regulators for selecting a lowest voltage from a plurality of drop-out voltages of said plurality of current regulators;

a feedback circuit for generating a feedback signal indicative of said lowest voltage; and

a DC-DC converter coupled to an external power source and said feedback circuit for supplying power to said plurality of diodes so as to allow said plurality of drop-out voltages of said current regulators to be forced to a predetermined voltage.

18. The driving circuit of claim 17 , wherein said selecting circuit further comprises:

a plurality of transistors coupled in parallel, wherein a plurality of bases of said plurality of transistors are coupled to said plurality of current regulators, respectively, such that a voltage of a plurality of collectors in common is indicative of said lowest voltage.

19. The driving circuit of claim 17 , further comprising:

an error amplifier coupled to said DC-DC converter and said feedback circuit for comparing said feedback signal and a predetermined signal indicative of said predetermined voltage so as to generate an output signal indicative of a difference between said lowest voltage and said predetermined voltage for determining said power.

20. The driving circuit of claim 17 , further comprising:

a bias controller operable for receiving said plurality of drop-out voltages and a plurality of specified current signals and for driving said plurality of current regulators according to said plurality of drop-out voltages and said specified current signals.

21. The driving circuit of claim 17 , wherein at least one of said plurality of drop-out voltages is different from the remaining drop-out voltages.