Generation from phase cut dimmer output with fast response to changes in dimmer position
A circuit for a dimmer system is disclosed, in which a phase-cut dimmer output signal is converted to a dimming control level signal. The phase-cut dimmer output signal is used to generated a pulse modulated signal indicative of the duty cycle of the phase cut dimmer output signal, and the pulse modulated signal is directly converted to a piece-wise linear dimming control level signal. By directly converting the pulse modulated signal to a piece-wise linear dimming control level signal, no further processing is necessary to produce a dimming signal which closely resembles the ideal logarithmic response of the human eye. A corresponding method for a dimmer system is also disclosed, as is a dimmer system.
1. A circuit for a dimming system, the circuit comprising:
an input for receiving a phase-cut dimmer output signal, the phase-cut dimmer output signal having a period and complementary cut and un-cut parts;
an output for outputting a dimming control level signal;
a comparator, connected to the input and arranged to produce a pulse-modulated signal from the phase-cut dimmer output signal, the pulse-modulated signal having an on-time which varies in dependence on the duration of the un-cut part; and
a converter configured to determine the dimming level control signal directly from the pulse-modulated signal, such that the dimming level control signal has a non-linear but piece-wise linear relationship with the un-cut part; and
wherein the converter is configured to determine the dimming level control signal by means of a variable frequency clock which increments or decrements a counter at each clock cycle during the on-time, and to determine the dimming level control signal from the counter.
2. A circuit according to claim 1 , wherein the clock is arranged to run at an initial rate during an initial part of the period which initial rate is in a fixed relationship with a base rate, and when the counter reaches a predetermined number, to terminate the initial part, set a flag, and reset the counter; the circuit being further configured to set the dimming control level signal to a fully dimmed level if the flag is not set.
3. A circuit according to claim 1 , wherein the clock is arranged to run at a first rate over a first part of the period and at a second rate over a second part of the period, wherein the first rate is in a fixed relationship with a base rate and the second rate in a fixed relationship with and higher than the first rate and the second part of the period is later in the period than the first part of the period.
4. A circuit according to claim 2 , wherein the clock is arranged to run at an initial rate during an initial part of the period which precedes both the first part and the second part in the period, and when the counter reaches a predetermined number, to terminate the initial part, set a flag, and reset the counter; the circuit being further configured to set the dimming control level signal to a fully dimmed level if the flag is not set.
5. A circuit according to claim 2 , further configured to operate a calibration phase in which the base rate is adjusted upwards period-by-period in response to the counter not reaching a second predetermined number during a period or the base rate is adjusted downwards period-by-period in response to the counter exceeding the second predetermined number during the period respectively.
6. A circuit according to claim 2 , further configured to operate a calibration phase in which the base rate is adjusted downwards period-by-period in response to the counter reaching a second predetermined number before the end of a period.
7. A controller for a dimmable lighting system comprising a phase-cut dimmer and a circuit as claimed in claim 1 .
8. A method of determining a dimming control level from a phase-cut dimmer output signal having a period and complementary cut and un-cut parts, the method comprising
determining a pulse-modulated signal from the phase-cut dimmer output signal, the pulse-modulated signal having an on-time which varies in dependence on the duration of the un-cut part; and
determining the dimming control level signal directly from the pulse modulated signal such that the dimming control level has a nonlinear piece-wise linear relationship with the cut part; and
wherein determining the dimming control level signal directly from the pulse modulated signal comprises
incrementing a counter of a variable frequency clock at each clock cycle during the on-time, and
determining the dimming level control signal from the counter.
9. The method of claim 8 , further comprising running the clock at an initial rate during an initial part of the period which initial rate is in a fixed relationship with a base rate,
and when the counter reaches a predetermined number, terminating the initial part, setting a flag, and resetting the counter;
and setting the dimming control level signal to a fully dimmed level if the flag is not set.
10. The method of claim 9 , further comprising running the clock at a first rate over a first part of the period and at a second rate over a second part of the period, wherein the first rate is in a fixed relationship with a base rate and the second rate in a fixed relationship with and higher than the first rate and the second part of the period is later in the period than the first part of the period.
11. The method of claim 10 , further comprising running the clock at an initial rate during an initial part of the period which precedes both the first part and the second part in the period,
and when the counter reaches a predetermined number, terminating the initial part, setting a flag, and resetting the counter;
and setting the dimming control level signal to a fully dimmed level if the flag is not set.
12. The method of any of claim 8 , further comprising operating a calibration phase in which the base rate is adjusted upwards period-by-period, in response to the counter not reaching a second predetermined number during a period or the base rate is adjusted downwards period-by-period in response to the counter exceeding the second predetermined number during the period respectively.
13. The method of claim 8 , further configured to operate a calibration phase in which the base rate is adjusted downwards period-by-period in response to the counter reaching a second predetermined number before the end of a period.