KR101382225B1 - Light emitting diode driving circuit without flicker - Google Patents

Abstract

According to an embodiment of the present invention, a dimmer for removing and outputting a part of the alternating current supplied from the alternating current power source; And a conduction angle detector for outputting a control signal for selectively conducting / blocking a current transmitted to the light emitting element in a specific conduction section of the dimmer conduction section.

Description

LIGHT EMITTING DIODE DRIVING CIRCUIT WITHOUT FLICKER}

The present embodiment relates to a light emitting device driving circuit in which flicker does not occur when illuminance is adjusted.

In driving a light emitting device, a dimmer is generally used to control the illuminance thereof. The dimmer removes and outputs a part of the current waveform supplied from the AC power source. For example, a part of the waveform may be removed immediately after the magnitude of the alternating current supplied from the AC power source passes through 0, or a part of the waveform immediately before passing through 0 may be removed.

The amount of current supplied to the light emitting device is controlled by the dimmer, thereby changing the amount of light emitted from the light emitting device. However, when there are many sections which are removed by the dimmer among the alternating currents provided for driving the light emitting device, the current consumption by the light emitting device becomes small, thereby causing a flicker phenomenon.

Therefore, it is urgent to develop a technology capable of preventing such a flicker phenomenon.

An object of the present invention is to solve all the problems of the prior art described above.

It is an object of the present invention to provide a light emitting device driving circuit in which flicker does not occur when illuminance is adjusted.

According to an embodiment of the present invention, the rectifier for rectifying the output waveform of the dimmer (removed) by removing a portion of the alternating current supplied from the AC power source; And a conduction angle detector for outputting a control signal for selectively conducting / blocking a current transmitted to the light emitting element in a specific conduction section of the dimmer from the output of the rectifier.

The conduction angle detector may output the control signal such that a current transmitted to the light emitting device is cut off when the time duration of the output waveform of the rectifier is positive is less than a threshold value.

The conduction angle detector may include: a level detector configured to output a high signal while the output waveform of the rectifier is maintained at a positive magnitude; And calculating a time for which the output signal of the level detector is kept high, comparing the calculated time with a threshold value, and determining whether to turn on / off the power supply unit for transmitting the output signal of the rectifier to the light emitting device. It may include a counter for outputting a signal.

The counter may output a low signal as a control signal for turning off the power supply when the time at which the output signal of the level detector lasts high is less than a threshold value.

The counter calculates, as the number of clocks, the time for which the output signal of the level detector remains high, and the threshold may be determined as the number of clocks.

The conduction angle detector may further include an oscillator for outputting the clock signal.

The conduction angle detector may output the control signal such that a current transmitted to the light emitting device is cut off when the maximum magnitude is less than a threshold value in a section in which the output waveform of the rectifier is continued with a positive magnitude.

The conduction angle detector includes: a comparator configured to output a high signal when an output waveform size of the rectifier is greater than a threshold; A latch for outputting the same signal as the output signal of the comparator at the start of the section until the start of the next section in which the output waveform of the rectifier is positive in magnitude; And a flip-flop that outputs the same signal as the output signal of the latch at the end of the section until the end of the next section and controls the on / off of the power supply unit transmitting the output signal of the rectifier to the light emitting device. It may include.

The conduction angle detector further includes a level detector for outputting a first pulse signal and a second pulse signal at a time point at which the interval starts and ends, and the first pulse signal is used as a reset signal of the latch. The second pulse signal may be used as a clock signal of the flip-flop.

The flip-flop outputs a high signal when the interval ends when the maximum size of the interval is greater than the threshold value, and the power supply unit may maintain the ON state only when the flip-flop is high.

The threshold value may be determined by setting by an external device or a drive circuit inside.

According to the present invention, the flicker phenomenon may be prevented when the illumination of the light emitting device is controlled by stopping the driving of the light emitting device in a section in which the flicker phenomenon may occur.

1 is a circuit diagram schematically illustrating a configuration of a general light emitting element driving circuit.
2 and 3 are graphs for explaining an operation example of a general dimmer.
4 is a circuit diagram illustrating a configuration of a light emitting device driving circuit according to an embodiment of the present invention.
5 is a graph for schematically describing an operation of a conduction angle detector in a light emitting device driving circuit according to an exemplary embodiment of the present invention.
6 is a view showing a first embodiment of a light emitting device driving circuit according to an embodiment of the present invention.
7 and 8 are timing diagrams showing waveforms of respective signals in the light emitting device driving circuit of FIG. 6.
9 is a view showing a second embodiment of a light emitting device driving circuit according to an embodiment of the present invention.
10 and 11 are timing diagrams showing waveforms of respective signals in the light emitting device driving circuit of FIG. 9.

DETAILED DESCRIPTION The following detailed description of the invention refers to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It should be understood that the various embodiments of the present invention are different, but need not be mutually exclusive. For example, certain features, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the invention in connection with an embodiment. It is also to be understood that the position or arrangement of the individual components within each disclosed embodiment may be varied without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is to be limited only by the appended claims, along with the full scope of equivalents to which such claims are entitled, if properly explained. In the drawings, like reference numerals refer to the same or similar functions throughout the several views.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, so that those skilled in the art can easily carry out the present invention.

[Preferred Embodiment of the Present Invention]

As used herein, the term "light emitting device" refers collectively to a device that converts electrical energy into light energy. In general, the light emitting device may be a light emitting diode (LED), but the present invention is not limited thereto. Any device capable of emitting light according to current flow can be used as a light emitting device of the present invention.

Light-emitting element drive circuit with general illumination control

Prior to describing the light emitting device driving circuit according to the embodiment of the present invention, a general light emitting device driving circuit will be described.

1 is a circuit diagram schematically illustrating a configuration of a general light emitting element driving circuit.

Referring to FIG. 1, the light emitting device driving circuit may include an AC power source 110, a dimmer 120, a light emitting device driving unit 130, and a light emitting device 140.

The dimmer 120 flows a current from the AC power source 110 to the light emitting device driver 130, and conducts and blocks the current for a predetermined period. In addition, the amount of light emitted from the light emitting device 140 may be adjusted through this. That is, the amount of light emitted from the light emitting device 140 is proportional to the magnitude of the flowing current. The amount of current used for driving the light emitting device 140 among the currents supplied by the dimmer 120 from the AC power source 110 is determined. By adjusting, the amount of light from the light emitting element 140 can be adjusted.

2 and 3 are graphs for describing an operation example of the dimmer 120.

As illustrated in FIGS. 2 and 3, the dimmer 120 may adjust the amount of power reaching the light emitting device 140 by removing a part of the current waveform from the AC power source 110.

First, referring to FIG. 2, the dimmer 120 may remove a portion of the waveform immediately after the magnitude passes 0 in the AC current supplied from the AC power source 110. This approach is called the leading edge dimmer 120 as it is.

In addition, referring to FIG. 3, the dimmer 120 may operate in a manner of removing a portion of the waveform immediately before the magnitude of the alternating current supplied from the AC power supply 110 passes zero. This approach is called a trailing edge dimmer 120 in its meaning.

In an ideal case, the light emitting device driver 130 should operate the light emitting device 140 normally in all cases until the conduction section of the dimmer 120 becomes 0% to 100%. That is, when the conduction section of the dimmer 120 is 0%, driving of the light emitting device 140 should be stopped. However, in reality, in a specific case where the conduction section of the dimmer 120 is 50% or less, the current consumption of the light emitting device 140 is reduced, thereby causing a flicker phenomenon.

Hereinafter, a light emitting device driving circuit according to an exemplary embodiment of the present invention for preventing the flicker phenomenon occurring when the conduction section of the dimmer 120 is small will be described.

Light emitting element driving circuit

4 is a circuit diagram showing the configuration of a light emitting element driving circuit according to an embodiment of the present invention.

Referring to FIG. 4, the light emitting device driving circuit according to the embodiment may include an AC power source 410, a dimmer 420, a rectifier 430, a power supply unit 440, a light emitting device 450, and a conduction angle detector 460. Include.

The dimmer 420 removes some of the current waveform from the AC power source 410. As described above, the dimmer 420 may remove a portion of the waveform immediately after the magnitude of the alternating current from the AC power source 410 passes zero, and may manually remove a portion of the waveform before passing the zero.

The rectifier 430 converts AC power passing through the dimmer 420 into DC power. That is, in FIG. 4, the rectifying unit 430 is implemented as a bridge diode composed of four diodes, but is not limited thereto. The rectifying unit 430 of the present invention may be used as long as it can convert an AC signal into a DC signal. Can be used as an element constituting

The power supply unit 440 transmits electric power for driving the light emitting device 450, and selectively transmits the electric power for driving the light emitting device 450 according to a control signal from the conduction angle detector 460. The power supply unit 440 may be implemented as a switch mode power supply (SMPS) that may be turned on / off according to an input control signal. Switch-mode power supplies can be implemented in many forms, such as buck converters or flyback converters. However, the present invention is not limited thereto, and any circuit capable of selectively transmitting or blocking power transmitted from the rectifying unit 430 according to a control signal may be used as the power supply unit 440 of the present invention.

The light emitting device 450 is driven by a current selectively transmitted by the power supply 440, and converts the electrical energy into light energy. The amount of light emitted from the light emitting device 450 may vary depending on the amount of current delivered. The light emitting device 450 may be implemented as a light emitting diode device, but is not limited thereto.

The conduction angle detector 460 outputs a control signal for determining on / off of the power supply unit 440 based on the output terminal voltage waveform of the rectifier 430.

5 is a diagram for schematically describing an operation of the conduction angle detector 460. Referring to FIG. 5, the conduction angle detector 460 outputs a control signal for turning off the light emitting device 450 at a predetermined conduction angle or less. That is, the light emitting device 450 is turned off in a section (a section of a certain conduction angle or less) including at least a conduction section in which a flicker phenomenon may occur among the conduction sections of the dimmer 420. In order to turn off the light emitting device 450, the power supply unit 440 may control to block the flow of current supplied to the light emitting device 450. For example, when the conduction angle of the dimmer 420 drops below 10%, the current supplied to the light emitting device 450 may be blocked.

Hereinafter, an embodiment of the conduction angle detector 460 will be described in detail.

Conduction angle The detection unit

1st Example

6 illustrates a light emitting device driving circuit of the present invention including the first embodiment of the conduction angle detector 460.

Referring to FIG. 6, the conduction angle detector 460 may include a level detector 461, a counter 462, and an oscillator 463.

7 and 8 are timing diagrams showing waveforms of respective signals in the light emitting device driving circuit of FIG. 6. 7 shows each signal waveform when the dimmer 420 is a leading edge dimmer, and FIG. 8 shows each signal waveform when the dimmer 420 is a trailing edge dimmer.

In the first embodiment, the power supply unit 440 is turned off when the AC power passing through the dimmer 420 and the rectifier 430 is smaller than the threshold value. The flicker phenomenon of the light emitting device 450 occurs when the amount of current applied is less than or equal to a predetermined value. The flickering time of the AC power passing through the dimmer 420 and the rectifier 430 is shorter than a predetermined amount. The reason is that the current magnitude in the corresponding section is small, so in this case, the current is blocked at all so that the flicker phenomenon can be prevented.

Specifically, the level detector 461 outputs a high signal as the output signal VDIM when the magnitude Vrect of the output signal waveform of the rectifier 430 is a positive value. When a large portion of the current removed from the AC power source 420 is removed by the dimmer 420, the time for which the magnitude is positive is shortened, whereby the output signal VDIM of the level detector 461 is reduced. The duration of the high is also shortened. Therefore, if the power supply unit 440 is turned off when the output signal VDIM of the level detector 461 lasts higher than the threshold value, the flicker of the light emitting device 450 may be prevented.

The counter 462 calculates, as the number of clocks, the time that the output signal VDIM of the level detector 461 lasts high, and accordingly outputs a control signal EN for turning on / off the power supply 440. Specifically, the counter 462 calculates, as the number of clocks, the time when the output signal VDIM of the level detector 461 is high based on the clock signal CLK from the oscillator 463. For example, referring to FIG. 7 and FIG. 8, the counter 462 sequentially turns the number of clocks when the output signal VDIM of the level detector 461 is high into four, three, three, and four. You can count.

On the other hand, the counter 462 turns on / off the operation of the power supply unit 440 according to the time that the output signal VDIM of the level detector 461 lasts high. For example, when the time at which the output signal VDIM of the level detector 461 lasts high is shorter than the threshold value, a low signal is output as the output signal EN and provided to the power supply unit 440, thereby providing a power supply unit ( 440 can be turned off, and when the time for which the output signal VDIM of the level detector 461 lasts high is longer than the threshold value, the high signal is output as the output signal EN and provided to the power supply 440. The power supply unit 440 may be turned on. Referring to the example shown in FIGS. 7 and 8, when three thresholds are provided as the number of clocks, the counter 462 has a clock number of times when the output signal VDIM of the level detector 461 lasts high. When the number is smaller than 3, the low signal can be output as the output signal EN. Thereafter, when the time at which the output signal VIM of the level detector 461 continues high is greater than three as the number of clocks, the high signal can be output as the output signal EN. The output signal EN of the counter 462 is provided as a control signal of the power supply 440. When the output signal EN of the counter 462 is high, the power supply 440 is an output signal of the rectifier 430. May be transmitted to the light emitting device 450 as it is, and if the output signal EN of the counter 462 is low, the power supply unit 440 may block a current transmitted to the light emitting device 450. The threshold may be provided by the user, but may be provided by other methods.

Oscillator 463 provides a clock signal CLK to counter 462. The frequency of the clock signal CLK may be determined by the input signal DIM_SET. The input signal DIM_SET as a control signal for determining the waveform of the clock signal CLK output from the oscillator 463 may be appropriately adjusted by the user. For example, the user may further reduce the current level for turning off the power supply 440 by adjusting the input signal DIM_SET to increase the frequency of the clock signal CLK, and conversely, the user may adjust the input signal DIM_SET. By appropriately adjusting and lowering the frequency of the clock signal CLK, the current level for turning off the power supply 440 may be relatively higher. However, the input signal DIM_SET for controlling the oscillator 463 is automatically provided according to, for example, an automatic detection of a condition in which the flicker of the light emitting device 450 occurs, or an operation time of the light emitting device 450, or the like. It may be modified. That is, the information may be automatically obtained without a user's input. In addition, the input signal DIM_SET for the control may be set by an external device or may be a set value present in the driving circuit (for example, at least one of the power supply unit 440 or the conduction angle detector 460). Can be.

As described above, since the threshold value can be set as the number of clocks, and the frequency of the clock signal CLK is set according to the input signal DIM_SET, the threshold value is set by the user, set by an external device, and inside the driving circuit. It can be said that it is determined by at least one of the setting of.

Second Example

9 illustrates a light emitting device driving circuit of the present invention including the second embodiment of the conduction angle detector 460.

Referring to FIG. 9, the conduction angle detector 460 may include a comparator 464, a level detector 465, a latch 466, and a flip-flop 467.

10 and 11 are timing diagrams showing waveforms of respective signals in the light emitting element driving circuit of FIG. 9. 10 shows each signal waveform when the dimmer 420 is a leading edge dimmer, and FIG. 11 shows each signal waveform when the dimmer 420 is a trailing edge dimmer.

In the second embodiment, the power supply unit 440 is turned off when the maximum magnitude in the section in which the AC power passing through the dimmer 420 and the rectifier 430 is positive is smaller than the threshold, and the magnitude is positive. If the maximum size in the section that continues as is greater than the threshold value it operates in a way to turn on the power supply 440. Since the flicker phenomenon of the light emitting device 450 occurs when the magnitude of the applied current is less than or equal to a predetermined value, if the maximum magnitude is smaller than the threshold value in a section where the AC power is positive, the current in the section is blocked at all. Flickering can be prevented by doing so.

Specifically, the comparator 464 compares the magnitudes of the reference signal DIM_SET and the input signal Vrect, and as an output signal Set when the input signal Vrect is larger than the magnitude of the reference signal DIM_SET. Outputs a high signal; otherwise, outputs a low signal. The output signal of the comparator 464 may be used as the set signal Set of the latch 466.

The comparator 464 may be implemented as an amplifier, and a reference signal DIM_SET may be input to the inverting input terminal, and a signal Vrect passing through the rectifier 430 may be input to the non-inverting input terminal. Since the signal passing through the rectifier 430 is a current signal, a resistor R for converting the signal into a voltage signal may be further included. For example, as shown in FIG. 9, a resistor R is connected between an output terminal of the rectifying unit 430 and a non-inverting input terminal of the comparator 464, and a resistor between the non-inverting input terminal of the comparator 464 and ground. (R) may be connected. In addition, the resistor R may be connected between the external power supply and the inverting input terminal of the comparator 464 and the resistor R may be connected between the inverting input terminal of the comparator 464 and the ground to provide the reference signal DIM_SET. have. The value of each resistor R may or may not be the same. The reference signal DIM_SET functions as a threshold of a current for turning off the power supply 440. By the operation described below, when the magnitude of the output signal waveform of the rectifier 430 is larger than the reference signal DIM_SET, the power supply unit 440 remains on, and the magnitude of the output signal waveform of the rectifier 430 is referenced. If it is smaller than the signal DIM_SET, the power supply unit 440 is turned off. The reference signal DIM_SET may be appropriately adjusted by the user. For example, by increasing the reference signal DIM_SET, the current level for turning off the power supply 440 may be further increased, and conversely, by lowering the reference signal DIM_SET, the current for turning off the power supply 440. You can also lower the level relatively. However, the reference signal DIM_SET may be automatically provided or modified according to, for example, an automatic detection of a condition in which the flicker of the light emitting device 450 occurs or an operation time of the light emitting device 450. That is, the information may be automatically obtained without a user's input. In addition, the reference signal DIM_SET functioning as the threshold value is set by an external external device or is present in the driving circuit (for example, at least one of the power supply unit 440 or the conduction angle detector 460). It may be a setting value.

That is, the threshold may be determined by at least one of a user input, a setting by an external device, and a setting inside the driving circuit.

The level detector 465 generates a pulse signal as the first output signal Reset when the magnitude of the output signal waveform Vrect of the rectifier 430 becomes a positive value, and the magnitude of the output signal waveform of the rectifier 430. When (Vrect) becomes 0, a pulse signal is generated as the second output signal CLK. That is, when the section in which the output signal waveform Vrect maintains the positive magnitude starts, the first output signal Reset is output, and when the section ends, the second output signal CLK is output. The first output signal Reset may be used as the reset signal Reset of the latch 466, and the second output signal may be used as the clock signal CLK of the flip-flop 467.

The latch 466 can be implemented as an RS latch. The reset signal Reset may be provided from the level detector 465, and the set signal Set may be provided from the comparator 464. As shown in FIGS. 10 and 11, the output signal RS_Q of the latch 466 is reset when the reset signal Reset is high. If the set signal Set is provided as a high signal when the reset signal Reset is not provided, the output signal RS_Q is thus output as a high signal, until the next reset signal Reset is provided, that is, The magnitude of the output signal waveform Vrect of the rectifier 430 is maintained until the start of the next section where the magnitude of the output signal waveform Vrect is positive.

As described above, the reset signal Reset signal is provided at the instant when the output signal Vrect waveform of the rectifier 430 becomes positive, and the set signal Set is applied to the output signal Vrect of the rectifier 430. Since the magnitude is greater than the threshold DIM_SET, the output signal RS_Q of the latch 466 starts from when the output signal Vrect of the rectifier 430 is greater than the threshold DIM_SET, and thus the rectifier 430. ) Remains high until the output signal (Vrect) magnitude of 0 becomes zero again.

The flip-flop 467 outputs the input signal RS_Q as an output signal Q in synchronization with the clock signal CLK. The flip-flop 467 may be implemented as a D-flip-flop, and the output signal RS_Q of the latch 466 may be used as an input signal of the flip-flop 467. As described above, the clock signal CLK is provided by the level detector 465, which is provided in synchronization with the time when the output waveform Vrect of the rectifier 430 becomes positive from zero. In other words, the output waveform Vrect of the rectifier 430 is provided in synchronization at the end of the period in which the positive duration continues.

The output signal EN of the flip-flop 467 functions as a control signal of the power supply unit 440. The output signal RS_Q of the latch 466 and the input signal of the flip-flop 467 start from when the output signal Vrect of the rectifier 430 is larger than the threshold value DIM_SET, and output signal of the rectifier 430. Since Vrect remains high until the magnitude becomes zero again, that is, until the next section starts, the maximum magnitude of the output signal Vrect of the rectifying unit 430 becomes a threshold value ( After a period greater than DIM_SET, the control signal EN may be made high in synchronization with the provided clock signal CLK. On the contrary, the control signal EN goes low after the section in which the maximum magnitude of the output signal Vrect of the rectifier 430 is smaller than the threshold value DIM_SET ends. That is, when the maximum magnitude in the section in which the output waveform Vrect of the rectifier 430 maintains the positive magnitude is larger than the threshold value DIM_SET, the output signal EN of the flip-flop 467 at the end of the section. Is output as a high signal, otherwise a low signal is output as the output signal EN. When the output signal EN of the flip-flop 467 is high, the power supply unit 440 is turned on to transmit the output signal of the rectifier 430 to the light emitting device 450 as it is, and the output signal of the flip-flop 467. If EN is low, the power supply 440 may be turned off to cut off the current delivered to the light emitting device 450.

As an embodiment of the above-described conduction angle detector 460, a method of conducting / blocking the current supplied to the light emitting device 450 according to a time in which the magnitude of the AC power passing through the dimmer 420 and the rectifier 430 is positive. The method of conducting / blocking the current supplied to the light emitting device 450 according to the maximum magnitude of the AC power passing through the dimmer 420 and the rectifier 430 has been described. In addition, the light emitting device 450 may prevent flicker. If it is a way to block the current transmitted to the light emitting device 450 under the conditions that can be seen will be said to belong to the scope of the present invention.

The features, structures, effects and the like described in the embodiments are included in at least one embodiment of the present invention and are not necessarily limited to only one embodiment. Furthermore, the features, structures, effects and the like illustrated in the embodiments can be combined and modified by other persons skilled in the art to which the embodiments belong. Therefore, it should be understood that the present invention is not limited to these combinations and modifications.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of illustration, It can be seen that various modifications and applications are possible. For example, each component specifically shown in the embodiments can be modified and implemented. It is to be understood that all changes and modifications that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

410: AC power
420: dimmer
430: rectifier
440: Power supply
450: light emitting element
460: conduction angle detector
461: level detector
462: counter
463: oscillator
464: comparator
465: level detection unit
466: latch
467: flip-flop

Claims (11)

A rectifier for rectifying an output waveform of a dimmer to remove and output a part of an alternating current supplied from an alternating current power source; And
A conduction angle detector configured to output a control signal for selectively conducting / blocking a current transmitted to a light emitting device in a specific conduction section of the dimmer conduction section from the output of the rectifier; And
Including a power supply for transmitting power for driving the light emitting device in response to the control signal,
The conduction angle detector outputs the control signal so that the current transmitted to the light emitting device is cut off by turning off the power supply when the time duration of the output waveform of the rectifier is positive is less than a threshold value. Element driving circuit. delete The method of claim 1,
The conduction angle detector,
A level detector for outputting a high signal while the output waveform magnitude of the rectifier is maintained at a positive magnitude; And
A control for calculating a time for which the output signal of the level detector lasts high, comparing the calculated time with a threshold value, and determining whether to turn on / off the power supply unit for transmitting the output signal of the rectifier to the light emitting device. A light emitting element driving circuit comprising a counter for outputting a signal. The method of claim 3,
And the counter outputs a low signal as a control signal for turning off the power supply when the time at which the output signal of the level detector lasts high is less than a threshold value. The method of claim 3,
And the counter calculates, as the number of clocks, the time for which the output signal of the level detector lasts high, and the threshold is determined as the number of clocks. 6. The method of claim 5,
The conduction angle detector,
And a oscillator for outputting the clock signal. A rectifier for rectifying an output waveform of a dimmer to remove and output a part of an alternating current supplied from an alternating current power source; And
A conduction angle detector configured to output a control signal for selectively conducting / blocking a current transmitted to a light emitting device in a specific conduction section of the dimmer conduction section from the output of the rectifier; And
And a power supply unit configured to transfer power for driving the light emitting device in response to the control signal.
The conduction angle detector outputs the control signal to turn off the power supply and cut off the current transmitted to the light emitting device when the length of the output waveform of the rectifier is less than a threshold value. Element driving circuit. 8. The method of claim 7,
The conduction angle detector,
A comparator for outputting a high signal when the magnitude of the output waveform of the rectifier is greater than a threshold;
A latch for outputting the same signal as the output signal of the comparator at the start of the section until the start of the next section in which the output waveform of the rectifier is positive in magnitude; And
Flip-flop for controlling the on / off of the power supply unit for outputting the same signal as the output signal of the latch at the end of the section until the end of the next section, the output signal of the rectifier to the light emitting element Light emitting device driving circuit comprising a. 9. The method of claim 8,
The conduction angle detector,
And a level detector for outputting a first pulse signal and a second pulse signal at a time point at which the interval starts and ends, respectively.
And the first pulse signal is used as a reset signal of the latch and the second pulse signal is used as a clock signal of the flip-flop. 9. The method of claim 8,
The flip-flop outputs a high signal at the end of the section when the maximum size in the section is greater than the threshold value, and the power supply unit maintains an ON state only when the flip-flop is high. Circuit. 8. The method of claim 1 or 7,
The threshold value is determined by a setting by an external device or a drive circuit inside.

Images