LED DIMMER CONTROL
A circuit dims an LED based on a duty cycle detected in an incoming power signal.
1 . A dimmer adapter, responsive to a dimming signal, for dimming an LED, the adapter comprising:
a duty-cycle estimator for estimating a duty cycle of an input power signal; and
a signal generator for producing a dimming signal in response to the estimated duty cycle.
2 . The dimmer adapter of claim 1 , further comprising a transformer type detector for detecting a type of a transformer used to generate the input power signal.
3 . The dimmer adapter of claim 2 , wherein the duty-cycle estimator estimates the duty cycle based at least in part on the detected transformer type.
4 . The dimmer adapter of claim 1 , wherein the duty-cycle estimator comprises a zero-crossing detector.
5 . The dimmer adapter of claim 4 , wherein the zero-crossing detector comprises a filter for filtering out a zero-crossing signal having a time period between consecutive zero crossings less than a predetermined threshold.
6 . The dimmer adapter of claim 1 , further comprising:
a phase-clip estimator for estimating phase clipping in the dimming signal; and
a bleeder control circuit for controlling a bleeder circuit based at least in part on the estimated phase clipping.
7 . The dimmer adapter of claim 6 , wherein the phase-clip estimator determines when the phase clipping starts based at least in part on a previously-observed cycle.
8 . The dimmer adapter of claim 7 , wherein the phase-clip estimator determines when the phase clipping ends based at least in part on a previously-observed cycle.
9 . The dimmer adapter of claim 7 , wherein the bleeder control circuit activates the bleeder circuit prior to the beginning of the phase clipping.
10 . The dimmer adapter of claim 9 , wherein the bleeder control circuit de-activates the bleeder circuit after the end of the phase clipping.
11 . A method for dimming an LED in response to a dimming signal, the method comprising:
estimating a duty cycle of an input power signal; and
producing a dimming signal in response to the estimated duty cycle.
12 . The method of claim 11 , further comprising detecting a type of a transformer used to generate the input power signal.
13 . The method of claim 11 , wherein estimating the duty cycle comprises detecting zero crossings of the input power signal.
14 . The method of claim 13 , further comprising filtering out high-frequency zero crossings.
15 . The method of claim 11 , further comprising estimating phase clipping in the dimming signal.
16 . The method of claim 15 , further comprising engaging a bleeder circuit during the phase clipping.
17 . The method of claim 16 , wherein the duty cycle is estimated while the bleeder circuit is engaged.