FIELD OF INVENTION

[0001] The present application relates to illumination field, in particular to a method and apparatus for controlling bleeder connected to phase-cut dimmer.

BACKGROUND OF THE INVENTION

[0002] Along with the development of the illumination technology, the dimmer is applied more and more widely. Fig. 1 shows a structural diagram of a typical dimmer system. As shown in Fig. 1 , the typical dimmer system comprises illumination apparatus, driver and dimmer, wherein, the driver is provided with dimming control circuit, and the dimmer may cut off phase of input voltage. Fig. 3 shows ideal and correct waveforms as detected. The dimming control circuit like microcontroller (referred to as MCU for short) may have a comparator which compares the phase detect signal to a fixed voltage V _ref and generates a comparison result. For example, when the phase detect signal is higher than the fixed voltage, the comparison result is 1 , when the phase detect signal is lower than the fixed voltage, the comparison result is 0. Based on the result, the MCU can measure the time duration of high level voltage of the phase detect signal and calculate the cutting-off phase. Fig. 4 (1) shows ideal phase detect signal in the case that the dimmer performs Trail, and Fig. 4 (3) shows ideal phase detect signal in the case that the dimmer performs Triac. The high level voltage duration time of the phase detect signal also stands for the dimmer's phase in that cycle. These are also the target waveforms desired to be obtained. With these waveforms, dimmer's phase can be measured accurately.

[0003] However, there is an output capacitor in the dimmer, which prevents the voltage from changing suddenly. As a result, the Trail waveform will be bad when the current to the driver is not big enough to discharge the capacitor quickly. In circuit of most drivers, there is an input capacitor which smoothes the voltage after the bridge. This capacitor makes a problem that when the input voltage is lower than the voltage of the capacitor, the capacitor cannot be charged so that there is litter input current during that time. As a result, the capacitor in the dimmer cannot be discharged quickly. The Fig. 4(2) shows bad phase detect signal in the event that the dimmer performs Trail and the Fig. 4(4) shows bad phase detect signal when the dimmer performs Triac. It can be seen that the phase as detected in Fig. 4 (2) and Fig. 4 (4) is longer than an ideal situation, which results a change of the dimming range. Therefore, such a condition shall be avoided. Usually, a bleeder resistor is used to discharge the capacitor in dimmers, as shown in Fig. 2. MCU outputs a high voltage used as control signal to bleeder to open the MOS bleeder (referred to as "open the bleeder" for short) when phase detect signal is lower than a fixed voltage V _ref . This current makes the capacitor discharge quickly. A dimming system including this bleeder circuit should have waveforms as Fig. 5 (1 ) and Fig. 5 (2).

[0004] Then, we can see the problem is solved in Triac, but there is nothing improved about Trail. We have to make high-level of bleeder control signal ahead of time (point 1 in Fig. 5(3)), so that the capacitor in dimmer can be discharged quickly, and the phase detect signal is similar to that in ideal situation.

[0005] Therefore, the moment for opening the bleeder (that is, moment which makes bleeder control signal to be high-level) needs to be found. In the conventional method, firstly, distinguish the dimming type from Triac and Trail. When the voltage ascends suddenly, the dimming type can be determined as Triac; if it drops suddenly, then the dimming type can be determined as Trail. This can be realized by the calculation of slope of input voltage V _in . Then, if it is Trail, when the sudden-change-point comes, as point 1 in Fig. 5, open the bleeder. This method has some weaknesses. First, the process is very complicated. It is needed to distinguish the dimming type from Triac and Trail and open the bleeder differently. It is needed to do lots of calculation to get the slope. All these will increase the code area requirement of MCU and speed requirement to reduce sample interval. This will increase difficulty to choose a suitable MCU and increase the cost of MCU. Second, MCU can not sample the voltage all the time. MCU takes time to run the code, i.e. to run the code in the sample interval. So the sample interval can not be very short. Normally, the code running time is 200 μ≤ to 300 μ≤. So sample interval will be longer than the code running time, which will result in a limit of the sample precision. The bleeder may open a bit later and the phase detected is longer, affecting the dimming precision.

[0006] It can be seen that there are technical problems of complicated process, large calculation and lower precision in the above technology. SUMMARY OF THE INVENTION

[0007] A brief summary about the present invention is provided hereinafter to provide basic understandings related to some aspects of the present invention. It shall be understood that this summary is not an exhaustive summary related to the present invention. The summary is not intended to determine a key part or an important part of the present invention, nor does it intend to limit the scope of the present invention. The purpose of the summary is only to provide some concepts in simplified forms to prelude more detailed descriptions discussed later.

[0008] A main object of the present invention is to provide a method for controlling a bleeder connected to a phase-cut dimmer and an apparatus for controlling a bleeder connected to a phase- cut dimmer.

[0009] According to one aspect of the present invention, a method for controlling a bleeder connected to a phase-cut dimmer is provided. Hereinafter the waveform change cycle of the input voltage of the phase-cut dimmer is referred to as an input voltage cycle. The method comprises: determining a first time period during which input voltage is lower than a predetermined reference voltage using at least one preceding input voltage cycle; opening the bleeder in the first time period in a later input voltage cycle; closing the bleeder in a second time period, wherein the second time period equals to the input voltage cycle minus the updated first time period, wherein the updated first time period equals to a sum of the first time period and a predetermined advancing time period; and repeating the steps of opening and closing the bleeder using the updated first time period.

[0010] According to another aspect of the present invention, an apparatus for controlling a bleeder connected to a phase-cut dimmer is further provided. Hereinafter the waveform change cycle of an input voltage is referred to as an input voltage cycle. The apparatus comprises: a first time period determining module for determining a first time period during which the input voltage is lower than a predetermined reference voltage using at least one preceding input voltage cycle; a first bleeder controlling module for opening bleeder in the first time period in a later input voltage cycle; a second bleeder controlling module for closing bleeder in a second time period, wherein the second time period equals to the input voltage cycle minus the an updated first time period, wherein the updated first time period equals to a sum of the first time period and a predetermined advancing time period; and a third bleeder controlling module for repeating the steps of opening and closing the bleeder using the updated first time period.

[0011] Furthermore, the embodiments of the present invention further provide a computer program product in at least computer readable medium form, on which computer program code for implementing the method for controlling the bleeder connected to phase-cut dimmer is recorded.

[0012] The present invention may control the bleeder connected to the phase-cut dimmer without distinguishing the dimming from the Triac and Trail, thereby simplifying processes and reducing calculation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Referring to the explanations of the present invention in conjunction with the

Drawings, the above and other objects, features and advantages of the present invention will be understood more easily. Components in the Drawings are only intended to illustrate the principle of the present invention. In the Drawings, the same or similar technical features or components are represented by the same or similar reference signs.

[0014] Fig. 1 is a block diagram showing a typical dimming system;

[0015] Fig. 2 is a circuit diagram showing a typical bleeder;

[0016] Fig. 3 shows ideal voltage waveform diagram of Triac and Trail;

[0017] Fig. 4 is voltage waveform diagram and phase detect signal waveform diagram without using bleeder to bleed;

[0018] Fig. 5 voltage waveform diagram and phase detect signal waveform diagram using bleeder to bleed;

[0019] Fig. 6 is a flow chart showing the method for controlling the bleeder connected to the phase-cut dimmer according to one embodiment of the present invention;

[0020] Fig. 7 is a flow chart showing the method for controlling the bleeder connected to the phase-cut dimmer according to embodiments of the present invention;

[0021] Fig. 8 shows voltage waveform diagram and phase detect signal waveform diagram when executing the method for controlling the bleeder connected to the phase-cut dimmer according to embodiments of the present invention;

[0022] Fig. 9 is a schematic view showing the time required by the voltage waveform to get a steady state; and

[0023] Fig. 10 is a block diagram showing an apparatus for controlling the bleeder connected to the phase-cut dimmer according to another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The embodiments of tlie present invention are discussed hereinafter in conjunction with the Drawings. Elements and features described in one Drawing or one embodiment of the present invention may be combined with elements and features described in one or more other

Drawings or embodiments. It shall be noted that representation and description of components and processes unrelated to the present invention and well known to one of ordinary skill in the art are omitted in the Drawings and the Description for the purpose of being clear.

[0025] Firstly, referring to Fig. 6, the method for controlling the bleeder connected to the phase-cut dimmer according to one embodiment of the present invention is described, wherein there is capacitor arranged in the phase-cut dimmer. Hereinafter the waveform change cycle of the Input voltage of the phase-cut dimmer is referred to as an input voltage cycle.

[0026] As shown in Fig. 6, in step 602, determine a first time period during which the input voltage is lower than a predetermined reference voltage using at least one preceding input voltage cycle. In step 604, open the bleeder in the first time period from the moment when the input voltage becomes lower than the predetermined reference voltage in a later input voltage cycle. In step 606, close the bleeder in a second time period from the moment when the input voltage becomes higher than the predetermined reference voltage, wherein the second time period equals to input voltage cycle minus an updated first time period, and the updated first time period equals to a sum of the first time period and the predetermined advancing time period. In step 608, repeat the steps of opening and closing the bleeder using the updated first time period.

[0027] Wherein, the advancing time period can be determined according to the time required for discharging the capacitor, wherein the capacitor may be output capacitor in the dimmer or input capacitor in the driver circuit, or both of the output capacitor and input capacitor. Output capacitor will prevent the voltage from changing suddenly and the input capacitor smoothes voltage after the bridge. However, the manner of determining the advancing time period is not limited thereto, and the advancing time period may be determined according to other appropriate manners.

[0028] The above updating the first time period and the repeating the steps of opening and closing the bleeder using the updated first time period may not necessarily be performed continuously for the continuous input voltage cycles. On the contrary, between two updates in the first time period, the first time period may keep unchanged in at least one cycle, and the unchanged first time period may be used to repeat the steps of opening and closing the bleeder. That is, two successive updates of the first time period are separated with N input voltage cycles, wherein N is an integer greater than or equal to 1. Wherein, the value of N is determined according to the time required by the output voltage of the phase-cut dimmer to get stable, frequency of the input voltage, and the time period during which the bleeder is in an open state.

[0029] It is described hereinafter referring to Figs. 7 and 8, wherein, Fig. 7 is a flow chart of one example showing the method for controlling the bleeder connected to phase-cut dimmer according to embodiments of the present invention, and Fig. 8 shows voltage waveform diagram and phase detect signal waveform when executing the method for controlling the bleeder connected to phase-cut dimmer according to embodiments of the present invention.

[0030] Firstly, when the input voltage V _in is lower than the reference voltage V _ref (in step 718 in Fig. 7, "phase detect signal becomes 0 from 1"), in step 720, dimmer control circuit (for example, MCU) opens the bleeder normally, that is, set the bleeder control signal as 1 . Then, the dimmer control circuit may record the time T _phase0 in Fig- 8(1), as shown in steps 718-722 in Fig. 7. Secondly, when the phase detect signal changes to high-level, the dimmer control circuit waits a time duration of T _{open_bleeder} which equals to T _phase0 minus T _{ear l ier} , and then open the bleeder, as shown in steps 712-716 in Fig. 7 and Fig. 8(2). T _phase1 will change accordingly, and shorter than T _phase0 . Thirdly, we may wait a few cycles. During this time, the bleeder opens only when phase detect signal is high-level, as shown in steps 702-710 in Fig. 7 and Fig. 5(2). T _{ph ase} time is hardly changeable. So waiting a few cycles may result a reduction of power. This will be described later. Fourthly, repeat the steps 718-722 and 712-716. T _phase will continue be shorter until the ideal dimmer phase, as shown in Fig. 8(3). Now, it will be a balance that T _phaseN equals to T _{phaseN - 1} , without being shorter, even when the bleeder opens ahead of time. Now, the desired waveform, that is, an ideal waveform, is obtained. We can use T _phase now as ideal dimmer phase in Fig. 4(1 ).

[0031] In Fig. 8(4), we can see that when bleeder opens T _earlier earlier, the voltage will not change because the dimmer has not cut-off the voltage. So this waveform is stable, similar to the ideal waveform in Fig. 4(3). As a result we get the desired waveform with the method of Triac and Trail.

[0032] But there is still a problem about this method. In Fig. 8(3) and 8(4), T _phase will not change and comes to stable. During part A, bleeder control signal has no voltage, so there is no current flowing through R _8bleeder , thus no bleeder consumption. During part B, there is no input voltage V _in , thus is no bleeder consumption. During part C, both input voltage V _in and Bleeder control signal have voltage. Suppose V _ref is 12V. There is no bleeder consumption when the bleeder opens when the bleeder instant power P _bleeder instant, input voltage V _in and current I _Rbleeder flowing through the bleeder satisfy the following relations:

[0033] P _{bleeder instant} =(Vin-12V)*I _Rbleeder =(Vin-12)* 12/R _bleeder ( 1)

[0034] Input voltage V _in can be high in terms of Trail, so the consumption is large. The value can be obtained according to the conversion of energy, because the energy is used to discharge the capacitor in the dimmer.

[0035] Supposed the time to discharge the capacitor is T _discharge , so through the following relation formula:

[0036] l/2*C*(Vin-12V)2=P _{bleeder instant} * T _discharge =(Vin-12)* 12/R _bleeder *T _discharge ,

[0037] we may obtain T _discharge =l/24*C*(Vm-12V)*R _bleeder (2).

[0038] Wherein, C is the capacitance of the capacitor in the dimmer.

[0039] When input voltage V _in is close to 12V, the instant power of the bleeder Pbieeder instant is small according to the above formula (1), as shown in Fig. 8(4). But the bleeder consumption can be large in terms of Trail. In terms of Trail, a typical capacitance value is 150nf, we suppose V _in is 350V and R _bleeder is 240 Ω (current of R _bleeder is 50mA). The frequency f _{openingbleeder} for opening the bleeder is 120Hz (60Hz of analogy input voltage). So during part C of Trail according to (2), there is the following result:

[0040] T _discharge = 1/24* 150 nf* ( 350-12V ) *240Ω=507 ps (3) [0041] P _{bleeder instant} = ( 350-I 2V ) *I2V/240Ω=16.9W (4)

[0042] Pbleeder ⁼ P _{bleeder instant} * T _discharge * f _{opening bleeder}

= 16.9W*507μs* 120 Hz=1.028W (5)

[0043] It can be seen that the bleeder power P _bleeder is large if we open the bleeder cycle by cycle, and further reduce the efficiency. Typically Pbieeder takes 10% of efficiency if the power of the driver is 10W. But we can reduce this value by reducing the frequency that we open the bleeder ahead of time (not open the bleeder normally). This is the third step we talked above. However, low frequency to pen bleeder ahead of time will result in a long time for the waveform to be stable state until T _phase is fixed. Provided that the time to be stable state is T _change , and the cutting-off phase is the biggest, as shown Fig. 9.

[0044] When the cutting-off phase of the phase-cut dimmer is the biggest, the total discharging time T _{total discharge} is close to a cycle period T _cycle , as Fig. 9. Suppose the time for opening the bleeder each time as T _discharge , so the times we should open the bleeder ahead of time Nearlier can be determined through the following formula:

[0045] N _earlier =T _{total-discharge} /T _discharge =T _cycle /T _discharge

[0046] Wherein, T _{total-discharge} is representative of the total discharging time of the capacitor, and T _cycle is representative of a time of one cycle.

[0047] As stated above, If we open the bleeder ahead of time every N cycles, then time we open the bleeder N _earlier is:

[0048] T _stable = N _ischarge * N *T _cycle = T _cycle * T _cycle / T _discharge * N

[0049] N = T _stable * T _discharge / (T _cycle * T _cycle )

[0050] Since the LED needs time to get stable when dimming, suppose T _stable is 1 second, the process of gradually restoring phase cannot be felt.

[0051] Typically, when input voltage is 60Hz, [0052] N - T _stable * T _discharge /(T _cycle *T _cycle )= 1s * 507 μs / (8.3ms * 8.3ms) = 7.3, we may take N =8.

[0053] Hereinafter, referring to Fig. 10, apparatus 1000 for controlling a bleeder connected to a phase-cut bleeder according to another embodiment of the present invention is described.

[0054] As shown in Fig. 10, the apparatus 1000 for controlling the bleeder connected to the phase-cut bleeder comprises: a first time period determining module 1002 for determining a first time period during which the input voltage is lower than a predetermined reference voltage using at least one preceding input voltage cycle; a first bleeder controlling module 1004 for opening the bleeder in the first time period from the moment when the input voltage becomes lower than the predetermined reference voltage in a later input voltage cycle; a second bleeder controlling module 1006 for closing the bleeder in a second time period from the moment when the input voltage becomes higher than the predetermined reference voltage, wherein the second time period equals to input voltage cycle minus updated first time period, wherein the updated first time period equals to the sum of the first time period and the predetermined advancing time period; and a third bleeder controlling module 1008 for repeating the steps of opening and closing the bleeder using the updated first time period.

[0055] The apparatus 1000 may further comprise an advancing time period determining module (not shown) for determining the advancing time period using the time required for discharging the capacitor.

[0056] Wherein, the third bleeder controller module 1008 may be further configured to make two successive updates of the first time period to be separated with N input voltage cycles, wherein N is an integer greater than or equal to 1.

[0057] The apparatus 1000 may further comprise times determining module for determining the value of N according to the time required by output voltage of the phase-cut dimmer to get stable, frequency of the input voltage, and the time period during which the bleeder is in open state.

[0058] According to the embodiments of the present invention, we do not need to distinguish the dimming type. Meanwhile, there is not a high demand of code area and speed in choosing dimming controller (like MCU), which reduces the cost, it does not need to make calculations all the time, but only 3 moments, which are shown in Fig. 7, wherein, the 3 moments are respectively the moment when the comparator phase detect signal becomes 1 from 0, the moment when the phase detect signal becomes 0 from 1, and the moment when opening the bleeder ahead of time. Those moments are triggered by interrupt of MCU, and relevant code can be run immediately in this interrupt.

[0059] Embodiments of the present invention will be applied to Triac and Trail. By applying embodiments of the present invention, the process of phase measuring may be simplified, preciseness may be improved and cost of the dimming controller circuit (for example MCU) may be reduced.

[0060] Based on the above understandings, the object of the present invention may be further achieved by running one program or a set of programs on any information processing device. The information processing device may be recognized universal devices. Therefore, the object of the present invention may also be achieved by only providing program product including program code implementing the method or device. That is, such a program produce also constitutes the present invention, and medium stored with or transmitting such a program product also constitutes the present invention. Apparently, the storage or transmission medium may be any type of storage or transmission medium well known to those skilled in the art, or later to be developed, so it is not necessary to list one by one various storage or transmission media here.

[0061] In the apparatus and method of the present invention, apparently, each component or each step may be disassembled, combined and/or recombined after being disassembled. Those disassembling and/or recombining shall be regarded as equivalent solutions of the present invention. It shall be further pointed out that the step performing the above series of processes may be executed naturally in time order according to the order of the Description, but not necessarily executed in time order. Some steps may be executed in parallel or independently from each other. Meanwhile, in the Description of the embodiments of the present invention, features described and/or illustrated for one embodiment may be used in one or more other embodiments in the same or similar manner, be combined with features in other embodiments or replace features in other embodiments. [0062] it shall be emphasized that the technical term "comprise/include" is used here to refer to an existence of a feature, an element, a step or a component, without excluding existences or attachments of one or more other features, elements, steps or components.

[0063] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, device, means, methods and steps described in the Description. As one of ordinarily skill in the art will readily appreciate from the disclosure contained in the invention, processes, devices, means, methods or steps presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, devices, means, methods, or steps.