System and method for driving LED

1. An integrated controller, comprising:

a filter configured to provide an output current signal;

a ramp generator configured to generate a reference ramp signal;

a first comparator coupled to the filter and to the ramp generator, wherein the first comparator is configured to compare the output current signal to the reference ramp signal and provide a first signal;

a second comparator coupled to the ramp generator, wherein the second comparator is configured to compare an output current set signal to the reference ramp signal and provide a second signal;

an error generator configured to provide an error signal based on a timing count between generation of the first and second signals;

a regulator configured to use the error signal to provide a control signal to control a dual phase cycle of a power converter at a constant frequency; and

a third comparator configured to compare the control signal with a sensed peak current level and to turn off a power switch when the sensed peak current level exceeds the control signal.

2. The integrated controller of claim 1 , further comprising:

an output current sensor configured to sense an output current level.

3. The integrated controller of claim 1 , further comprising:

a digital-to-analog converter coupled to the regulator and to the third comparator, wherein the digital-to-analog converter is configured to provide the control signal to the third comparator as an analog control voltage.

4. The integrated controller of claim 1 , further comprising:

a buffer coupled to the third comparator and configured to drive the power switch.

5. The integrated controller of claim 1 , further comprising:

an output voltage sensor configured to sense an output voltage level.

6. The integrated controller of claim 1 , wherein the filter comprises an RC circuit.

7. The integrated controller of claim 1 , wherein the reference ramp signal has a constant frequency.

8. A method of controlling a switching power converter for supplying power to one or more light emitting diodes (“LEDs”), the method comprising:

turning a power switch on to provide current through an inductor and the power switch;

measuring ampseconds of the inductor at an off time;

generating a periodical ramp signal at a constant frequency;

comparing the measured ampseconds with the periodical ramp signal and generating a first signal when the periodical ramp signal exceeds the measured ampseconds;

comparing a set reference signal with the periodical ramp signal and generating a second signal when the periodical ramp signal exceeds the set reference signal;

generating a signed digital error based on a difference between when the first signal or the second signal is generated;

using the signed digital error, generating a digital control signal;

converting the digital control signal into an analog peak current reference signal;

sensing a peak current through the power switch;

comparing the peak current to the peak current reference signal; and

turning the power switch off.

9. The method of claim 8 , further comprising:

regulating LED brightness by sensing an optical output of the LED;

generating an optical output signal; and

adjusting the set reference signal to maintain the optical output signal substantially constant.

10. The method of claim 8 , further comprising:

regulating contrast of an illuminated area by sensing optical ambient;

generating an optical ambient signal; and

adjusting the set reference signal proportionally to the optical ambient signal.

11. The method of claim 8 , further comprising:

regulating LED brightness over thermal effects by sensing an LED junction temperature;

generating a temperature signal; and

adjusting the reference signal using a look-up table comprising emission versus LED temperature performance.

12. The method of claim 8 , wherein the period of the ramp signal is greater than a time period starting when the switch is turned on and ending when the switch is turned off.

13. A method of controlling a switching power converter for supplying power to one or more light emitting diodes (“LEDs”), the method comprising:

turning a power switch on to provide current through an inductor and the power switch;

measuring voltseconds of the inductor at an off time;

generating a periodical ramp signal at a constant frequency;

comparing the measured voltseconds with the periodical ramp signal and generating a first signal when the periodical ramp signal exceeds the measured voltseconds;

comparing a set reference signal with the periodical ramp signal and generating a second signal when the periodical ramp signal exceeds the set reference signal;

generating a signed digital error based on a difference between when the first signal or the second signal is generated;

using the signed digital error, generating a digital control signal;

converting the digital control signal into an analog peak current reference signal;

sensing a peak current through the power switch;

comparing the peak current to the peak current reference signal; and

turning the power switch off.

14. The method of claim 13 , further comprising:

regulating LED brightness by sensing an optical output of the LED;

generating an optical output signal; and

adjusting the set reference signal to maintain the optical output signal substantially constant.

15. The method of claim 13 , further comprising:

regulating contrast of an illuminated area by sensing optical ambient;

generating an optical ambient signal; and

adjusting the set reference signal proportionally to the optical ambient signal.

16. The method of claim 13 , further comprising:

regulating LED brightness over thermal effects by sensing an LED junction temperature;

generating a temperature signal; and

adjusting the reference signal using a look-up table comprising emission versus LED temperature performance.

17. The method of claim 13 , wherein the period of the ramp signal is greater than a time period starting when the switch is turned on and ending when the switch is turned off.