LED controllers, drivers and lighting circuits
A controller for controlling a plurality of LED lighting strings is disclosed, the controller comprising, for each of the plurality of LED lighting strings: a frequency modulator configured to modulate a baseline frequency to generate a time-vary modulated frequency, wherein the frequency modulator is configured to modulate the baseline frequency by a jitter superposed on a regular repeating pattern which varies more slowly than the jitter, to result in the modulated frequency; and a modulated PWM signal generator configured to generate a modulated PWM signal having the modulated frequency and a predetermined duty cycle; wherein the regular repeating patterns for the PWM signals are spaced apart in phase. Associated drivers, LED lighting circuits and methods are also disclosed.
1. A controller for controlling a plurality of LED lighting strings,
the controller comprising, for each of the plurality of LED lighting strings:
a frequency modulator configured to modulate a baseline frequency to generate a time-varying modulated frequency,
wherein the frequency modulator is configured to modulate the baseline frequency by a jitter superposed on a regular repeating pattern which varies more slowly than the jitter, to result in the modulated frequency; and
a modulated PWM signal generator configured to generate a modulated PWM signal having the modulated frequency and a predetermined duty cycle;
wherein the regular repeating patterns for the PWM signals are spaced apart in phase.
2. A controller as claimed in claim 1 , wherein the jitter is random.
3. A controller as claimed in claim 1 , wherein each frequency modulator comprises:
a jitter module configured to adjust the respective baseline frequency by a random amount; and
an envelope shaper module configured to adjust the respective baseline frequency according to a regular repeating pattern, operable in combination with the jitter module.
4. A controller as claimed in claim 3 , wherein each envelope shaper is configured to adjust the respective baseline frequency by the same regular repeating pattern.
5. A controller as claimed in claim 1 , wherein each regular repeating pattern is the same one of a triangular and a saw-tooth pattern.
6. A controller as claimed in claim 1 , wherein the regular repeating pattern for different PWM signals are evenly spaced apart in phase.
7. A controller as claimed in claim 1 , further comprising a phase-lock circuit to lock the phases of the regular repeating pattern for different PWM signals.
8. A driver for driving a plurality of LEDs lighting strings, comprising a controller as claimed in claim 1 , and a plurality of power switches, each configured to be switched according to the respective modulated PWM signal.
9. A driver as claimed in claim 8 , further comprising a measuring unit, configured to determine a period of time when none of the modulated PWM signals are high, and to measure a characteristic of a one of the LED lighting strings within the period.
10. A driver as claimed in claim 9 , wherein the characteristic is temperature.
11. A lighting circuit comprising a driver as claimed in claim 1 and further comprising the plurality of LED lighting strings.
12. A method of controlling a plurality of LED lighting strings,
the method comprising, for each of the plurality of LED lighting strings:
modulating a baseline frequency to generate a time-vary modulated frequency,
wherein the baseline frequency is modulated by a jitter superposed on a regular repeating pattern which varies more slowly than the jitter, to result in the modulated frequency;
and generating a modulated PWM signal having the modulated frequency and a predetermined duty cycle;
wherein the regular repeating patterns for the PWM signals are spaced apart in phase.
13. The method of claim 12 , wherein the jitter is random.
14. The method of claim 12 , wherein each regular repeating pattern is the same regular repeating pattern.
15. The method of claim 12 , further comprising determining a period of time when none of the modulated PWM signals are high, and measuring a characteristic of a one of the LED lighting strings within the period.