EP1767067A1

EP1767067A1 - Lamp-dimming through bypassing of phase-cutting

Info

Publication number: EP1767067A1
Application number: EP05748050A
Authority: EP
Inventors: Xichun Zhang; Fengkang Hu; Shihai Zhu
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2004-07-08
Filing date: 2005-06-15
Publication date: 2007-03-28
Also published as: CN1719963A; WO2006006085A1; JP2008506226A; CN1981564A

Abstract

A dimmer arrangement (10) to be coupled to a ballast that controls a lamp has bypassing means (30) for bypassing phase-cut means (20). The bypassing means (30) bypasses the phase-cut means (20) when not being actuated, and activates the phase-cut means (20) for a dimming time period when being actuated. Therefore, by bypassing the phase cut means during a period of non-actuation, for most of the time no phase cutting occurs so that harmonics are greatly reduced as well as the electromagnetic interference and that during the phase cutting only a fixed cut angle is used, which preferably is just above the smallest detectable phase cut angle.

Description

LAMP-DIMMING THROUGH BYPASSING OF PHASE-CUTTING

The invention relates to a dimmer arrangement comprising phase- cut means for cutting phase angles in cycles of an AC power supply signal, the phase-cut means being coupled in series with an AC power supply line for carrying the AC power supply signal.

The invention further relates to a ballast comprising a dimmer arrangement, to a lamp comprising a ballast, and to a lamp socket comprising a ballast.

Such a dimmer arrangement is known from U.S. Pat. No. 5559395. The known dimmer arrangement is used widely in lamp dimming. In the abovementioned patent, a phase control triac dimmer is provided. The triac dimmer is coupled in a power supply line. A series circuit consisting of a variable resistor and a capacitor is coupled in parallel with the triac for firing the triac at an arbitrarily selected angle for phase conduction. A diac is coupled between a node of the variable resistor and the capacitor, and the gate of the triac. By varying the resistance of the variable resistor, the phase angle of an AC voltage is controlled. The dimmer clips or blocks a portion of each half cycle of the AC voltage immediately after the zero crossing of the voltage and the portion or angle of the half cycle is adjustable. With this triac dimmer, the phase angle of the AC voltage can be adjusted and a different phase-cut angle corresponds to a different lighting level. However with this triac dimmer, in dimming situations, every half cycle of the power supply is cut with an arbitrary selected angle. Therefore, harmonic distortion and electromagnetic interference (EMI) cannot be avoided, in particular when the selected angle is large. When the conduction phase angle is small, i.e. the phase-cut angle is large, the lamp will possibly be flickering. It is an object of the invention to provide a dimmer arrangement with less harmonic distortion.

To this end, the dimmer arrangement is characterized in that it comprises bypassing means for bypassing the phase-cut means, the bypassing means being arranged to bypass the phase-cut means when not being actuated, and to activate the phase-cut means for a dimming time period when being actuated.

The invention is based on the insight that by bypassing the phase cut means during a period of non-actuation, for most of the time no phase cutting occurs so that harmonics are greatly reduced as well as the electromagnetic interference and that during the phase cutting only a fixed cut angle is used, which preferably is just above the smallest detectable phase cut angle. An embodiment of a dimmer arrangement according to the invention is characterized in that the phase cut angles are fixed. With a fixed phase-cut angle, a ballast circuit controlled by the dimmer arrangement does not have to take into account the value of phase-cut angle, so it can just determine the dimming time period; For minimizing interference, the phase cut angle can be selected as the minimum detectable angle for dimming.

Another embodiment of a dimmer arrangement according to the invention is characterized in that the phase-cut means is arranged to cut either positive or negative halves of the cycles. Phase cutting in only one half cycle can also convey the dimming information due to the fact that the frequency of AC power supply is high. In this way, the harmonic distortion and electromagnetic interference in the circuit are reduced even more during the dimming time period as compared to cutting both positive and negative half cycles. Another embodiment of a dimmer arrangement according to the invention is characterized in that the bypassing means comprises first actuation means for activating the phase cut means at a frequency of the AC power supply signal, and second actuation means for activating the phase cut means at double the frequency of the AC power supply signal, the first and second actuation being coupled in series. The two actuation means are arranged to transfer different information for dimming.

Another embodiment according to the invention provides a ballast in combination with the dimmer arrangement according to the present invention, the ballast comprising a dimming controller for controlling dimming with a control signal, characterized in that the dimming controller is arranged to adjust the control signal in accordance with the dimming time period. The ballast controls dimming according to the dimming time period instead of using power supplied to the ballast, so, for dimming, the control of power supplied to the lamp is realized at the output of the ballast circuit instead of at the input of the ballast circuit. Herewith, harmonic distortion in the ballast circuit is reduced.

These and other aspects of the invention will be apparent from and elucidated further with reference to the embodiments described by way of example in the following description and with reference to the accompanying drawing, in which

Fig 1 shows a first embodiment of a dimmer arrangement 10 according to the invention;

Fig 2A shows a second embodiment of a dimmer arrangement 110 according to the invention;

Fig 2B shows waveforms of several certain voltage signals in dimmer arrangement and ballast according to the invention;

Fig. 3A shows a third embodiment of a dimmer arrangement 210 according to the invention; Fig 3B shows the waveform of voltage of outputted from a dimmer arrangement according to the invention;

Fig. 4 shows a forth embodiment of a dimmer arrangement 310 according to the invention; Fig 5 shows a block diagram of ballast according to the invention; and

Fig. 6 shows an embodiment of extracting means 463 according to the invention.

Same reference numerals are used to denote similar parts throughout the figures. Fig 1 shows a first embodiment of a dimmer arrangement 10 according to the invention. Dimmer arrangement 10 comprises a dimmer 20 and bypassing means 30. Dimmer 20 is a phase cut dimmer, such as triac dimmer, a thyristor dimmer, a power switch dimmer or a MOSFET dimmer.

Under normal operating conditions, bypassing means 30 is not actuated. As a result, dimmer 20 is bypassed by bypassing means 30, i.e., dimmer 20 is inoperative . In a dimming situation, bypassing means 30 is actuated. Then , AC current passes through dimmer 20, and dimmer 20 cuts phase angles of AC power supply signal AC during a dimming time period

DTP. So, under normal operating conditions, no phase cutting occurs in AC power supply signal AC, and no harmonic distortion occurs from phase cutting, whereas during dimming harmonic distortion is kept minimal.

Fig 2A shows a second embodiment of a dimmer arrangement 110 according to the invention. Dimmer arrangement 110 comprises a triac dimmer 120 and bypassing means 130. Triac dimmer 120 comprises resistors R1 and R2, and a capacitor C1 coupled in parallel with a triac 140 for firing triac 140 at a fixed phase cut angle PCA for phase conduction. A diac 150 is coupled between the resistors R1 and R2 and the gate of triac 140. Bypassing means 130 comprises a push button P1. Under normal operating conditions, button P1 is not actuated, i.e., AC current passes through button P1 , and triac dimmer 120 is bypassed. Therefore no phase cutting occurs in AC power supply signal AC.

In a dimming situation, a user actuates button P1 for a dimming time period DTP according to a required illumination.

During the dimming time period DTP, triac dimmer 120 is coupled into AC power supply line A. During positive half-cycles of AC power supply signal AC, capacitor C1 is charged positively and the voltage Vd across capacitor C1 rises to the triggering voltage of diac 150. With positive triggering of diac 150, triac 140 is fired after a fixed delay angle (namely the phase cut angle, PCA) of the positive half-cycle of AC power supply signal AC. During negative half-cycles of AC power supply signal AC, capacitor C1 is charged negatively and voltage Vd decreases to the negative triggering voltage of diac 150. With negatively triggering of diac 150, triac 140 is fired after a fixed delay angle (namely the phase cut angle, PCA) of the negative half-cycle of AC power supply signal AC. The fixed delay angle is determined by R1 , R2, C1 and the trigger voltage of diac 150.

The voltage waveform Vin of AC power supply signal AC cut by dimmer 120 is shown in FIG 2B as the voltage VAB. For comparing input voltage Vin is also shown in FIG 2B. Under normal operating conditions, the voltage waveform of VAB is the same as the waveform of Vin. In dimming situation, every half cycle of the voltage waveform of VAB is cut with a phase cut angle PCA. Phase cutting occurs only during dimming time period DTP, i.e., the time period the user pushes button P1. Outside dimming period DTP, there is no phase cutting, i.e., AC power supply signal AC has full cycles. Therefore under normal conditions, no harmonic distortion is generated. Further shown in Fig 2B are voltage Vs, VAB, Vs, Vk, Vf, Vc, VD and reference voltage Vrefi and Vref2 and CLK that will be described with reference to Fig 5 and Fig 6. Fig. 3A shows a third embodiment of a dimmer arrangement 210 according to the invention. Compared with dimmer arrangement 110, in dimmer arrangement 210, a thyristor 240 is used to replace triac 140 and a diode 232 is arranged parallel to button P1. When button P1 is actuated, every positive half cycle of AC power supply signal AC is cut by a phase cut means 230 with a fixed phase cut angle PCA. The voltage of AC power supply signal AC at terminals A and B is shown in Figure 3B. If thyristor 240 and diode 232 are coupled oppositely directions, every negative half cycle of

AC power supply signal AC is cut by the phase cut means with a fixed phase cut angle PCA.

Fig. 4 shows a forth embodiment of a dimmer arrangement 310 according to the invention. Compared with dimmer arrangement 110, another button P2 is coupled with button P1 in series and is arranged parallel with a diode 342. When button P1 is actuated, phase cut means 320 works the same as phase cut means 120 as shown in Fig 2A. If only button

P2 is actuated, phase cut means 320 works the same as phase cut means 220 as shown in Fig 2A. So separate actuation of buttons P1 and P2 causes different phase cutting of AC power supply signal AC.

In this way, different information according to dimming time period DTP can be conveyed by a phase cut AC power supply signal AC. Buttons P1 and P2 may represent different requirements of the user. Actuation of button

P1 may represent brightening and actuation of button P2 may represent dimming, and vice versa. Also, actuation of button P1 may represent dimming, while actuation of P2 may represent other function, such as color adjustment of the lamp. Buttons P1 and P2 may be buttons that are directly operable by a user, or remotely operable switches operable through remote control unit, such as a well-known infrared remote control device.

In the above embodiments of dimmer arrangements, a variable resistor may be introduced for adjusting phase cut angle PCA. Fig 5 shows a block diagram of ballast 400 according to the invention. Ballast 400 is used in combination with a dimmer arrangement provided in the present invention. Ballast 400 comprises an EMI filter 410 for filtering electromagnetic interference, a rectifier 420 for rectifying AC power supply signal AC into DC power supply signal DC, a power factor controller 430 for controlling a power factor, an inverter controller 440 for controlling an inverter, and an inverter 450 for converting DC voltage into a high frequency AC voltage to actuate a lamp.

Ballast 400 also comprises a dimming controller 460 for controlling dimming. Dimming controller 460 comprises extracting means 463 for extracting dimming signal D-SIG from an output 422 of rectifier 420, and signal processing means 456 for converting dimming signal D-SIG into control signal C-SIG.

The output 422 of rectifier 420, namely the voltage Vs, DC power signal DC, is shown in Fig. 2B. During dimming time period DTP, DC power signal DC carries a dimming signal D-SIG with a fixed phase cut angel PCA.

Extracting means 453 extracts from DC power supply DC a dimming signal

D-SIG, namely the voltage Vc, as shown in FIG. 2B.

Signal processing means 456 comprises a clock generator 468 for generating a clock signal CLK, shown in Fig 2B. After receiving dimming signal D-SIG from extracting means 453, signal processing means 456 processes dimming signal D-SIG according to clock signal CLK, e.g. by counting the number of pulse signals or counting the time period of the dimming signal D-SIG, and outputs a control signal C-SIG, namely Vd, as shown in Fig 2B.

Control signal C-SIG is inputted to inverter controller 440. Inverter controller 440 is a conventional inverter control IC, such as half bridge control IC which is easily available in the market. In normal situation, inverter controller 440 controls the frequency of the inverter with a current signal O-SIG. In a dimming situation, after controller signal C-SIG is inputted to inverter controller 440, current signal O-SIG is changed according to control signal C-SIG. In a normal situation, control signal inputted to inverter controller 400 is regarded as zero or other value with no effect on current signal O-SIG of inverter controller 400. Inverter controller 440 operates according to the current signal O-SIG.

Fig. 6 shows an embodiment of extracting means 463 according to the invention. Extracting means 463 comprises two comparators A1 and A2 and a low-pass filter comprising resistor R3 and R4 and a capacitor C2. When voltage VS, the voltage of DC power signal DC from rectifier

420, is lower than the reference voltage Vrefl , comparator A1 outputs a high level voltage VK. When voltage VS is higher than reference voltage Vrefl , comparator A1 outputs a low level voltage VK. The waveform of voltage Vk is shown in FIG 2B. When voltage VK passes the low-pass filter formed by R3, R4 and C2, unwanted pulse signals are eliminated. In Figure 2B, unwanted pulses are relatively narrow pulses outside dimming time period DTP and pulses after relatively wide pulses in dimming time period DTP. The waveform of VF, the output of the low-pass filter, is shown in Fig 2B. Low-pass filtered VF is compared with reference voltage Vref2 in comparator A2. Then comparator

A2 outputs a pulse signal (i.e. dimming signal) corresponding with the dimming time period DTP, namely Vc as shown in Fig 2B. Then Vc , the dimming signal , is inputted to signal processor 466 .

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be constructed as limiting the claim. The word

'comprising' does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several distinct elements and by means of a suitable programmed computer. In the unit claims enumerating several means, several of these means can be embodied by one and the same item of hardware. The usage of the words first, second and third, etcetera do not indicate any ordering. These words are to be interpreted as names.

Claims

What is Claimed is:

1. A dimmer arrangement (10) comprising phase-cut means (20) for cutting phase angles (PCA) in cycles of an AC power supply signal (AC), the phase-cut means (20) being coupled in series with an AC power supply line (A) for carrying the

AC power supply signal (AC) , characterized in that the dimmer arrangement (10) comprises bypassing means (30) for bypassing the phase-cut means (20), the bypassing means (30) being arranged to bypass the phase-cut means (20) when not being actuated, and to activate the phase-cut means (20) for a dimming time period (DTP) when being actuated.

2. A dimmer arrangement (10) as claimed in Claim 1, wherein the cut phase angles (PCA) are fixed.

3. A dimmer arrangement as claimed (10) in Claim 1 , wherein the phase-cut means (20) is arranged to cut positive and negative halves of the cycles of the AC power supply signal (AC).

4. A dimmer arrangement (10) as claimed in Claim 1 , wherein the phase-cut means (20) is arranged to cut either positive or negative halves of the cycles of the AC power supply signal (AC).

5. A dimmer arrangement (10) as claimed in claim 1 , characterized in that the bypassing means (30) comprises first actuation means (P1) for activating the phase cut means (30) at a frequency of the AC power supply signal (AC), and second actuation means (P2; 342) for activating the phase cut means (30) at double the frequency of the AC power supply signal (AC), the first and second actuation means (P1 ; P2 and 342) being coupled in series.

6. A dimmer arrangement (10) as claimed in claim 5, characterized in that actuation for the dimming time period (DTP) occurs at either actuation of the first actuation means (P1) or the second actuation means (P2;342), and actuation for a brightening period occurs at either actuation of the second actuation means (P2;342) or the first actuation means (P1).

7. A ballast (400) in combination with a dimmer arrangement (10) as claimed in any one of claims 1 to 4, the ballast (400) comprising a dimming controller (460) for controlling dimming with a control signal (C- SIG), characterized in that the dimming controller (460) is arranged to adjust the control signal (C-SIG) in accordance with the dimming time period (DTP).

8. A ballast (400) as claimed in Claim 7, characterized in that the dimming controller (460) comprising clock generating means (468) for generating a clock signal (CLK) and that the dimming controller (460) is arranged to determine the control signal (C-SIG) by counting clock periods of the clock signal during the dimming time period (DTP).

9. A lamp characterized in that the lamp comprises a ballast (400) as claimed in Claim 7.

10. A lamp characterized in that the lamp comprises a ballast (400) as claimed in Claim 8.

11. A lamp socket characterized in that the lamp socket comprises a ballast (400) as claimed in Claim 7.

12. A lamp socket characterized in that the lamp socket comprises a ballast (400) as claimed in Claim 8.

13. A dimming control method comprising cutting phase angles in cycles of power supply signal, converting phase cut angles into a control signal, and dimming according to the control signal, characterized in that the method further comprises only cutting the phase angles during a dimming time period, and determining the control signal in accordance with the dimming time period.