Signalling Method for Dimmers Controlling a Load

Abstract

A signalling method for a plurality of dimmers controlling a load connected in series with an alternating current (AC) source, whereby each of the plurality of dimmers are connected in parallel with each other. The method includes: receiving a user control signal from an initiating one of the plurality of dimmers indicating a command for at least one of the plurality of dimmers; the initiating one of the plurality of dimmers generating one or more signalling pulses on a control waveform for at least one half cycle of the AC to the load based on the user control signal; each of the plurality of dimmers except the initiating one of the dimmers detecting the one or more signalling pulses for the at least one half cycle of the AC; and each of the plurality of dimmers except the initiating one of the dimmers determining the command based on the one or more signalling pulses for the at least one half cycle of the AC.

Claims

1. A signalling method for a plurality of dimmers controlling a load connected in series with an alternating current (AC) source, whereby each of the plurality of dimmers are connected in parallel with each other, the method includes: receiving a user control signal from an initiating one of the plurality of dimmers indicating a command for at least one of the plurality of dimmers; the initiating one of the plurality of dimmers generating one or more signalling pulses on a control waveform for at least one half cycle of the AC to the load based on the user control signal; each of the plurality of dimmers except the initiating one of the dimmers detecting the one or more signalling pulses for the at least one half cycle of the AC; and each of the plurality of dimmers except the initiating one of the dimmers determining the command based on the one or more signalling pulses for the at least one half cycle of the AC.

2. The signalling method according to claim 1, further including: the initiating one of the plurality of dimmers altering a conduction period of the control waveform for said at least one half cycle of the AC to the load for the one or more signalling pulses based on the user control signal; each of the plurality of dimmers except the initiating one of the dimmers detecting a change in the conduction period for the at least one half cycle of the AC; and each of the plurality of dimmers except the initiating one of the dimmers determining the command based on the change in the conduction period for the at least one half cycle of the AC.

3. The signalling method according to claim 2, further including the initiating one of the dimmers increasing the conduction period of the control waveform by a designated period to form one of the signalling pulses for each of the least one half cycle of the AC to the load.

4. The signalling method according to claim 3, wherein increasing the conduction period by the designated period includes advancing a start of the conduction period of a following half cycle of the AC to the load by advancing turn-ON of the load for the following half cycle.

5. The signalling method according to claim 3, further including the initiating one of the dimmers increasing the conduction period for a designated number of half cycles of the AC to the load based on the user control signal.

6. The signalling method according to claim 5, further including detecting the increase in the conduction period for the designated number of half cycles of the AC and determining the command based on the designated number of half cycles of the AC to the load.

7. The signalling method according to claim 6, wherein the designated number of half cycles of the AC to the load includes consecutive half cycles of the AC.

8. The signalling method according to claim 2, further including detecting a zero-crossing of the AC to the load and tracking the conduction period of the load for each half cycle of the AC based on a duty cycle of the zero-crossing of the AC to the load.

9. The signalling method according to claim 8, further including detecting the change in the conduction period for the at least one half cycle of the AC based on a change in the duty cycle of the zero-crossing of the AC to the load.

10. The signalling method according to claim 2, further including detecting a rate of change in voltage at each of the plurality of dimmers exceeding a threshold rate indicative of the change in the conduction period for the at least one half cycle of the AC.

11. A dimming system for controlling a load, the dimming system including: a plurality of dimmers connected in series with the load and an alternating current (AC) source, whereby each of the plurality of dimmers are connected in parallel with each other, wherein each of the plurality of dimmers has a user interface and a dimmer circuit for controlling AC to the load, and wherein the dimmer circuit includes: a controller configured to: receive a user control signal from the user interface indicating a command for at least one of the plurality of dimmers, wherein if the controller of an initiating one of the plurality of dimmers receives the user control signal, the controller of the initiating one of the dimmers generates one or more signalling pulses on a control waveform for at least one half cycle of the AC to the load based on the user control signal, the controller of each of the plurality of dimmers except the initiating one of the dimmers detects the one or more signalling pulses for the at least one half cycle of the AC and determines the command based on the one or more signalling pulses for the at least one half cycle of the AC.

12. The dimming system according to claim 11, wherein the controller of the initiating one of the dimmers alters a conduction period of the control waveform for the at least one half cycle of the AC to the load for the one or more signalling pulses based on the user control signal; and the controller of each of the plurality of dimmers except the initiating one of the dimmers detects the change in the conduction period for the at least one half cycle of the AC and determines the command based on the change in the conduction period for the at least one half cycle of the AC.

13. The dimming system according to claim 12, wherein the controller of the initiating one of the dimmers increases the conduction period of the control waveform by a designated period to form one of the signalling pulses for each of the least one half cycle of the AC to the load.

14. The dimming system according to claim 13, wherein increasing the conduction period by the designated period includes advancing a start of the conduction period of a following half cycle of the AC to the load by the controller advancing turn-ON of the load for the following half cycle.

15. The dimming system according to claim 13, wherein the controller of the initiating one of the dimmers increases the conduction period for a designated number of half cycles of the AC to the load based on the user control signal.

16. The dimming system according to claim 15, wherein the controller of each of the plurality of dimmers except the initiating one of the dimmers detects the increase in the conduction period for the designated number of half cycles of the AC and determines the command based on the designated number of half cycles of the AC.

17. The dimming system according to claim 16, wherein the designated number of half cycles of the AC to the load include consecutive half cycles of the AC.

18. The dimming system according to claim 12, wherein the controller is further configured to detect a zero-crossing of the AC to the load and to track the conduction period of the load for each half cycle of the AC based on a duty cycle of the zero-crossing of the AC to the load.

19. The dimming system according to claim 18, wherein the controller is further configured to detect the change in the conduction period for the at least one half cycle of the AC based on a change in the duty cycle of the zero-crossing of the AC to the load.

20. The dimming system according to claim 12, wherein the controller is further configured to detect a rate of change in voltage at each of the plurality of dimmers exceeding a threshold rate indicative of the change in the conduction period for the at least one half cycle of the AC.

21. The dimming system according to claim 20, wherein the controller includes a signalling receiver circuit configured to detect the rate of change in voltage at each of the plurality of dimmers.

22. A signalling method for a plurality of dimmers controlling a load connected in series with an alternating current (AC) source, whereby each of the plurality of dimmers are connected in parallel with each other, the method includes: receiving a user control signal from an initiating one of the plurality of dimmers indicating a command for at least one of the plurality of dimmers and the load; the initiating one of the plurality of dimmers generating one or more signalling pulses on a control waveform for at least one half cycle of the AC to the load based on the user control signal; the load detecting the one or more signalling pulses for the at least one half cycle of the AC; and the load determining the command based on the one or more signalling pulses for the at least one half cycle of the AC.

23. A dimming system for controlling a load, the dimming system including: a plurality of dimmers connected in series with the load and an alternating current (AC) source, whereby each of the plurality of dimmers are connected in parallel with each other, wherein each of the plurality of dimmers has a user interface and a dimmer circuit for controlling AC to the load, and wherein the dimmer circuit includes: a controller configured to: receive a user control signal from the user interface indicating a command for at least one of the plurality of dimmers, wherein if the controller of an initiating one of the plurality of dimmers receives the user control signal, the controller of the initiating one of the dimmers generates one or more signalling pulses on a control waveform for at least one half cycle of the AC to the load based on the user control signal, a controller of the load detects the one or more signalling pulses for the at least one half cycle of the AC and determines the command based on the one or more signalling pulses for the at least one half cycle of the AC.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0034] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0035] FIG. 1 shows a dimming system for controlling a load according to an embodiment of the present invention;

[0036] FIG. 2A shows a block diagram of a dimmer of the dimming system of FIG. 1;

[0037] FIG. 2B shows a block diagram of a dimmer of the dimming system of FIG. 1;

[0038] FIG. 3 shows signals of a dimming system for controlling a load in an OFF state according to an embodiment of the present invention where the load is a resistive load;

[0039] FIG. 4 shows signals of a dimming system for controlling a load in an ON state according to an embodiment of the present invention where the load is a capacitive load;

[0040] FIG. 5 shows waveforms of an initiating one of the plurality of dimmers in the dimming system of FIG. 1;

[0041] FIG. 6 shows signalling pulses for designated half cycles of the AC indicative of commands according to an embodiment of the present invention;

[0042] FIG. 7 is a block diagram of a controller of a dimmer of a dimming system according to an embodiment of the present invention;

[0043] FIG. 8 is a circuit diagram of a zero-cross detector circuit of the controller of FIG. 7;

[0044] FIG. 9 is a circuit diagram of a signalling receiver circuit of the controller of FIG. 7; and

[0045] FIG. 10 is flow chart of a signalling method for a plurality of dimmers controlling a load according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0046] FIG. 1 shows an embodiment of a dimming system 10 for controlling a load having a plurality of dimmers S.sub.1-S.sub.N, whereby each of the plurality of dimmers S.sub.1-S.sub.N are connected in parallel with each other and the plurality of dimmers S.sub.1-S.sub.N are connected in series with the load and an alternating current (AC) source. As discussed, the load is preferably a driver for LED lights and the user controls brightness of the LED lights using each of the multi-way dimmers S.sub.1-S.sub.N. Also, the dimmers are preferably trailing edge phase control dimmers for controlling the LED lights.

[0047] FIG. 2A shows an embodiment of one of the dimmers S.sub.1 in more detail, which has a dimmer circuit 11 for controlling alternating current (AC) to the load. The dimmer S.sub.1 also has a user interface 12 for a user to control the brightness of the load and to input other commands. Further, it will be appreciated by those persons skilled in the art that the dimming system of FIG. 1 could be representative of a room with multiple entry ways and each of the dimmers S.sub.1-S.sub.N are multi-way dimmers that allow a user to control brightness of the LED lights in the room independently from each of the dimmers at the entry ways. The dimmer circuit 11 includes a controller 13 configured to perform a number of steps to implement control of the load by controlling an AC switch 14.

[0048] FIG. 2B shows a further embodiment of one of the dimmers S.sub.1 in more detail, which has a dimmer circuit 11 for controlling alternating current (AC) to the load. The dimmer S.sub.1 also has a user interface 12 for a user to input commands, such as controlling the brightness of the load or to enter setup modes. Preferably, the dimmers S.sub.1-S.sub.N are 2-wire trailing edge phase control dimmers for controlling brightness of a light source, such as a LED light source. It will be appreciated by those persons skilled in the art that N can be any number of dimmers wired in parallel, with N being limited by the light source load not illuminating due to the combined OFF state leakage current of the N dimmers. It will also be appreciated that the load can be an inductive, capacitive or resistive load. In one embodiment, for instance, the load is a driver for Light Emitting Diode (LED) lights and is a capacitive load. In another embodiment, the dimmers S.sub.1-S.sub.N are 2-wire leading edge phase control dimmers and the load is inductive. In yet another embodiment, the load is an incandescent lamp and is a resistive load; in this embodiment, either all leading or all trailing edge phase control dimmers are suitable.

[0049] In the embodiment of FIG. 2B, the dimmer circuit 11 includes a number of further circuits rather than the controller 13 to implement control of the load. It will be appreciated by those persons skilled in the art that many circuits of the dimmer circuit 11 do not affect operation of the multi-way dimming system and thus will not be discussed in detail herein. The circuits of the dimmer circuit 11 that affect operation include an AC switch 14 for switching the AC to the load at a conduction angle to control the load. The AC switch 14 applies line voltage to the load only during a selected conduction period within each polarity of AC voltage half-cycle. That is, the AC is conducted to the load in an ON state and not conducted to the load in an OFF state, and the ON state is a conduction period and the OFF state is a non-conduction period.

[0050] The dimmer control circuit 11 also includes a timing control circuit 16 configured to determine the conduction angle of load to control turn-OFF and turn-ON at each cycle of the AC to control switching of the ON and OFF states of the AC switch 14. The timing control circuit 16 determines the conduction angle of the load based on at least a user control signal from the user interface 12 indicating the conduction angle of the load. For example, the user interface 12 is a rotary knob of a dimmer connected to a rotary encoder. The rotary encoder provides the user control signal in response to the user rotating the knob of the dimmer to arrive at a desired brightness of the LED lights.

[0051] The user control signal from the user interface 12 also indicates a command for at least one of the dimmers S.sub.1-S.sub.N. As discussed, for instance, the user inputted a desired brightness of the LED lights via the user interface which provides a user control signal indicating the initiator pulse signalling command. This command signals to the controller of each of the plurality of dimmers except the initiating one of the dimmers to relinquish control to the initiating dimmer and await the new conduction angle. The rotary knob can also be depressed a designated number of times to provide other commands. For instance, the user wishing to transmit a set up command for the other dimmers depresses the knob once to providing the set up command. In another example, the user interface 12 is a press-switch or some other interface of a dimmer that is connected to an encoder. The encoder here also provides the user control signal in response to the user pressing or otherwise interacting with the user interface of the dimmer.

[0052] The dimmer circuit 11 further includes a zero-cross detection circuit 18 configured to detect a zero-crossing of the AC and a conduction angle control circuit 20. The zero-crossing of the AC is used by the conduction angle control circuit 20 to determine the conduction periods and the non-conduction periods of the AC. The zero-cross detection circuit 18 thus provide an instantaneous timing indication of line voltage zero-crossing in each AC voltage half-cycle. The conduction angle control circuit 20 is subsequently configured to track the conduction angle of the load by detecting a change in the conduction angle of the load based on the conduction periods and the non-conduction periods of the AC. The zero-crossing of the AC occurs when the AC line voltage equals zero between the two polarities of the half cycles. In the multi-way dimming system 10, for all non-initiator dimmers—whether in the ON-state or OFF-state—their respective zero-cross detection circuits 18 provide an indication of the prevailing conduction angle of a present initiator dimmer.

[0053] The dimmer circuit 11 also includes a rectifier (not shown) for rectifying the AC power in the non-conduction period to generate rectified dimmer voltage to be provided to the dimmer circuit 11. Also, the timing control circuit 16 of the dimmer circuit 11 has two circuits: a gate drive circuit (not shown) and a conduction period timing circuit (not shown). The gate drive circuit has a number of further circuits for controlling turn-OFF and turn-ON of the AC switch 14 at each half cycle of the AC to control switching of the load ON and OFF states. The rectifier and the gate drive and conduction period timing circuits may adopt various configurations known in the art without affecting the working of the dimming system 10 other than providing voltage to the dimmer circuit 11 and thus will not be further discussed.

[0054] It will be appreciated by those persons skilled in the art that the timing control circuit 16, as shown in FIG. 2B, includes switching elements, which are MOSFET switching devices. For example, the MOSFETs are high voltage (600V) N-channel MOSFETs (e.g. FCPF11N60), which are used to control the amount of power delivered to the load. Two of these MOSFETs are configured so that they alternately control power delivery to the load over the different polarity half cycles of AC power. That is, each of the MOSFETs turn-ON and turn-OFF the switching circuit 12 at each cycle of the AC, respectively, so that the load (e.g. a driver for LED down lights) is dimmed in proportion to the amount of time in each cycle that the AC switch 14 is switched OFF.

[0055] In use of the system 10, if the initiating one of the plurality of dimmers S.sub.1 receives a user control signal from the user interface 12 indicating for example an increase in brightness, the user control signal thus also includes an initiator pulse signalling command for the remaining dimmers S.sub.2-S.sub.N in the system 10. The controller 13 of the initiating one of the dimmers S.sub.1 communicates the signal by generating signalling pulses on a control waveform for half cycles of the AC to the LED lights based on the user control signal. More specifically, the timing control circuit 16 increases a conduction period of the control waveform by a designated period of 0.1 ms to form a signalling pulse for the next half cycle and for 7 more successive half cycles of the AC to the load (i.e. for 80 ms) based on this user control signal. The timing control circuit 16 of the initiating one of the dimmers S.sub.1 increases the conduction period for 8 consecutive half cycles of the AC to the load by modifying turn-ON of the load for these 8 half cycles of the AC to the load. Modifying the turn-ON, in this embodiment, involves the timing control circuit 16 advancing a start of the conduction period for each half cycle of the AC to the load by advancing turn-ON of the load by the designated period of 0.1 ms to form the signalling pulse.

[0056] The controller 13 of each of the dimmers S.sub.2-S.sub.N detects the 8 signalling pulses as advances in the conduction period for 0.1 ms for 8 half cycles of the AC and determines the command based on these signalling pulses. As described, the controller 13 detects the increase in the conduction period for 8 half cycles of the AC and determines the command based on the 8 half cycles of the AC—in this case, an initiator pulse signalling command.

[0057] FIG. 4 show signals of the dimming system 10 for controlling a load where the load is in the ON state. Here, it can be seen that the timing control circuit 16 of the initiating one of the dimmers S.sub.1 generates signalling pulses on the control waveform for half cycles of the AC to the load. The conduction periods of the control waveform are increased by 0.1 ms—as shown on the ON-state Load Current with signalling waveform—to form signalling pulses for 6 consecutive half cycles based on this user control signal. As described, the timing control circuit 16 of the initiating one of the dimmers S.sub.1 increases these conduction periods by advancing a start of the conduction period for the half cycles of the AC to the load by the signalling increment of 0.1 ms.

[0058] FIG. 3 show signals of the dimming system 10 for controlling a load where the load is in the OFF state. Specifically, FIGS. 3 and 4 illustrate example control waveforms associated with the dimming system 10 where the dimmers are trailing edge phase control multi-way dimmers. When the load is in the OFF state, as shown in FIG. 3, the controller 13 of the initiating one of the dimmers S.sub.1 can still generate signalling pulses on a control waveform for half cycles of the AC to the load based on the received user control signal. Here, the timing control circuit 16 turns-ON the load at very low conduction angles at the zero-crossings of the AC to the load by the designated period of 0.1 ms to form the signalling pulses for the next half cycle and for successive half cycles of the AC to the load based on this user control signal. The 0.1 ms signalling pulses are not able to be visually detected when used with respect to LED lights and thus the dimming system 10 can be controlled while the LED lights are OFF using this method.

[0059] In one embodiment, the controller 13 detects the signalling pulses that are advances in the conduction period with the zero-cross detection circuits 18 of the dimmers S.sub.2-S.sub.N, which detect a change in the zero-crossing of the AC in response to the new conduction periods. The zero-cross detection circuits 18 track the conduction periods of the load for each half cycle of the AC based on a duty cycle of the zero-crossing of the AC to the load, and detect the change in the conduction period for the half cycles of the AC based on a change in the duty cycle of the zero-crossing of the AC to the load.

[0060] In addition, zero-cross detection circuits 18 can track the conduction periods of the load for each half cycle of the AC to adopt a new conduction angle for the load. For example, upon determination of the initiator pulse command by the zero-cross detection circuits 18 detecting 8 consecutive signalling pulses, each of the plurality of dimmers S.sub.2-S.sub.N except the initiating dimmer S.sub.1 turns-OFF AC to the AC switch 14 and relinquishes control to the initiating dimmer S.sub.1 so that a new conduction angle of the load can be established and later followed by the each of the plurality of dimmers S.sub.2-S.sub.N. That is, in this example, timing control circuit 16 of the initiating dimmer S.sub.1 determines a new conduction angle of the load based on the user control signal to increase brightness and the timing control circuit 16 of the dimmer S.sub.1 uses the new conduction angle which subsequently affects the zero-crossing of the AC for the load. The zero-cross detection circuit 18 of each of the plurality of dimmers S.sub.2-S.sub.N except the initiating dimmer S.sub.1 detects a change in the duty cycle of the zero-crossing of the AC in response to the new conduction angle. The corresponding conduction angle control circuit 20 of the dimmers S.sub.2-S.sub.N tracks this new conduction angle by detecting the change in the conduction angle of the load and the timing control circuit 16 of each the dimmers S.sub.2-S.sub.N adopts the new, desired conduction angle.

[0061] In another embodiment, the controller 13 detects the signalling pulses that are advances in the conduction period by detecting a rate of change in voltage at each of the dimmers S.sub.2-S.sub.N exceeding a threshold rate indicative of the change in the conduction period for the at least one half cycle of the AC. The controller 13 includes a signalling receiver circuit shown in FIG. 9 to detect the rate of change in voltage exceeding a threshold rate of say 1V/μs.

[0062] FIG. 5 shows the change in voltage across one of the dimmers S.sub.1-S.sub.N during a signalling pulse, where the normal, relatively slow, rate of change of voltage at about 0.1V/μs is substantially increased by a factor of up to 100 to about 10V/μs. In comparison to normal line voltage, the signalling receiver circuit can detect signalling pulses where the timing of the zero-cross detection is advanced by at least 100 μs. To allow for the filtering effects of capacitance associated with some lighting load types, the signalling receiver is responsive to zero-crossing dimmer voltage dv/dt as slow as 1V/μs. Hence, as above, the threshold rate is set at 1V/μs.

[0063] To generate a signalling pulse, the timing output of the zero-cross detection circuit 18 advances the zero-crossing of the next half cycle and for a designated number of following half cycles of the AC to the load by about 100 μs. This corresponds to a very fast decrease in dimmer voltage at each of the dimmers S.sub.1-S.sub.N from around 10V (to 0V), of around at least 1V/μs, but up to 101V/μs, which is detectable by the above mentioned signalling receiver circuits of the dimmers S.sub.2-S.sub.N. The respective controllers 13 of the dimmers S.sub.2-S.sub.N detect the increase in the conduction period in this way for the designated number of half cycles of the AC and thus can determine the command based on the detected designated number of half cycles of the AC.

[0064] FIG. 6 shows an example of different commands and their corresponding signalling pulses. For example, the set up selection command is selected by a user by say pressing once on the user interface 12 and has a designated signalling period of 40 ms consisting of four 0.1 ms signalling pulses over consecutive half cycles. Other commands are detailed in the table below

TABLE-US-00001 Period of Command Signalling Purpose Setup Selection  40 ms Determine which feature is being changed in Setup Mode. 1 signalling period = 1 user click during Setup Selection Mode (feature selection). Initiator Pulse  80 ms Used during Normal and Setup signalling Mode to signal all other dimmers to Turn Off and Follow. This is the primary signalling mechanism. spare 110 ms not currently used Setup Cancel 150 ms Cancel Setup Mode Setup Save and Exit 200 ms Save any changed settings and Exit Setup Mode Setup Mode Dimmer 250 ms All Dimmers enter Setup Mode Setup Mode Timer 300 ms All Minute Timers enter Minute Setup Mode Setup Mode Timer 350 ms All Hour Timers enter Hour Setup Mode Setup Mode Switch 400 ms All Switch products enter Setup Mode

[0065] FIG. 7 shows an embodiment of a controller of the dimmers S.sub.1-S.sub.N in the dimmer system 10 in the form of a microprocessor implementing at least part of the dimmer circuit 11. That is, in this embodiment, each of the dimmers S.sub.1-S.sub.N have a user interface 12, such as a knob that is cable of being pressed and is connected to a rotary encoder for generating the user command signals, to permit input of commands and adjustment of load conduction angle. The microcontroller also outputs to a zero cross detection circuit shown in FIG. 8 and receives input from the signalling receiver circuit shown in FIG. 9 described above.

[0066] In more examples of the system 10 in use, it will be appreciated that the load can be initially either in the ON or OFF state. If the load is in the OFF state, any of the dimmers S.sub.1-S.sub.N can be the initiating dimmer S.sub.1 by the user rotating or pressing the knob so that the corresponding initiating dimmer S.sub.1 generate the signalling pulses to the other dimmers S.sub.2-S.sub.N. In the example where the non-initiating dimmers S.sub.2-S.sub.N stay in the OFF state indefinitely, these signalling pulses are redundant. Also, in the example where the non-initiating dimmers stay in the OFF state indefinitely and the load is in the ON state, the initiating dimmer S.sub.1 is the only dimmer in the system 10 in the ON state. The user, however, can control the load from any one of the other dimmers S.sub.2-S.sub.N by rotating or pressing the knob of a dimmer to turn that dimmer into the ON state. The new initiating dimmer S.sub.1′ then generates the signalling pulses to the other dimmers including the old initiating dimmer S.sub.1 to revert to the OFF-state so that the new initiating dimmer S.sub.1′ can control the load to control the brightness by rotating the knob and to turn the load OFF by depressing the knob.

[0067] FIG. 8 shows an embodiment of a zero-cross detection circuit described above that used to advance the half-cycle conduction period for signalling purposes and can also be used for detection purposes. During normal zero-cross detection without signalling pulses, the signalling enable input is low; therefore transistor Q7 is not driven and consequently transistor Q6 has no conduction. Transistor Q1 is however permanently biased and enabled to conduct collector current at about 0.3 mA through resistor R1 and emitter resistor R2. The base bias current for Q1 is provided by resistor R3, where bias voltage is determined by transistor Q2 in conjunction with resistive voltage divider R5 and R6. At non-zero (rectified) dimmer voltage, collector current remains available to transistor Q1 and therefore Q1 base terminal does not significantly load the emitter voltage of transistor Q2. Transistor Q2 therefore remains in conduction state and drives transistor Q3, which in turn acts to pull low the output buffer stage comprising transistors Q4 and Q5, so that zero-crossing signal output is low. When the signalling enable indicating a signalling pulse to Q7 is set high, this enables additional transistor Q6 to conduct, provided that the rectified dimmer voltage exceeds about 10V. The timing output of zero-cross detector therefore advances by about 100 μs—corresponding to dimmer voltage of about 10V—so that commencement of the dimmer half-cycle conduction period is advanced accordingly.

[0068] FIG. 9 shows the signalling receiver circuit used to detect signalling pulses as described. The rectified dimmer voltage is applied to a resistive voltage divider comprising R1 and R2, having divider ratio of about 0.17, so that a 10V amplitude signalling transition appears as a 1.7V transition at base terminal of receiver transistor Q1. A Diode D1 is used to clamp the maximum voltage at output of voltage divider. The receiver transistor Q1 is configured as an emitter follower with emitter resistor R3; therefore the received voltage transition also appears at Q1 emitter. A differentiator circuit comprising R4 and Cl is used to couple the received voltage transition to base terminal of pnp transistor Q2 which functions as a voltage comparator circuit. The capacitance value of Cl and resistance value of R4 are selected such that Q2 is driven into conduction state if the signalling voltage transition dv/dt is at least the threshold rate of 1V/us. The output from Q2 is used to trigger a monostable pulse generator comprising Q3, Q4 and associated components, to generate a nominal 0.1 ms pulse to signify the presence of the signalling pulse.

[0069] Referring now to FIG. 10, there is shown a summary of a signalling method 100 for a plurality of dimmers controlling a load connected in series with an alternating current (AC) source, whereby each of the plurality of dimmers are connected in parallel with each other. The method 100 includes: receiving 102 a user control signal from an initiating one of the plurality of dimmers indicating a command for at least one of the plurality of dimmers; the initiating one of the plurality of dimmers generating 104 one or more signalling pulses on a control waveform for at least one half cycle of the AC to the load based on the user control signal; each of the plurality of dimmers except the initiating one of the dimmers detecting 106 the one or more signalling pulses for the at least one half cycle of the AC; and each of the plurality of dimmers except the initiating one of the dimmers determining 108 the command based on the one or more signalling pulses for the at least one half cycle of the AC.

[0070] Further aspects of the method will be apparent from the above description of the dimming system 10. A person skilled in the art will also appreciate that at least parts of the method 100 could be embodied in program code for implementation on the above mentioned microprocessor. The program code could be supplied in a number of ways, such as on a memory of the dimmer circuit 11 in data communication with the microprocessor, and could be configured to be implemented by the microprocessor implementing at least part of the dimmer circuit 11.

[0071] It will be understood that there may be other variations and modifications to the configurations described herein that are also within the scope of the present invention.

[0072] The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing context for the present invention. It is not suggested or represented that any of these matters formed part of the prior art base or were common general knowledge as it existed before the priority date of each claim of this application.