JP2011108668A - Led dimming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LED dimming apparatus which hardly generates noises even when an LED current is large, and which hardly causes irregularities in brightness even if dimming is intensified. <P>SOLUTION: When a dimming signal outputted from a dimmer 1 is on a higher side of a predetermined brightness level, a current flowing through an LED load 4 is to be a continuous current, and the light of the LED load 4 is controlled by the magnitude of the flowing current. When the dimming signal outputted from the dimmer 1 is on a lower side of the predetermined brightness level, the current flowing through the LED load 4 is made to be a pulsed current, and the light of the LED load 4 is controlled by varying an average value of its waveform. The predetermined level is set so that a ratio of a voltage change to a current change in V-I characteristics of the LED load is within a range of three to five times as compared with the time of flowing a rated current. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an LED dimming device that uses a light emitting diode (hereinafter referred to as “LED”) as a light source and has a dimming function.

  As a conventional LED light control device, there is one disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2003-157986). This conventional example is a combination of control of the voltage applied to the LED and switching dimming by a switch element that intermittently switches the LED current. When the dimming signal from the outside is received by the control circuit and the degree of dimming is shallow (when bright), the voltage applied to the LED is kept constant and the dimming is performed by changing the ON / OFF DUTY of the switch element. When the degree of dimming is deep (when dark), the switch element ON / OFF DUTY is kept constant, and the voltage applied to the LED is variably controlled for dimming.

When the dimming is performed by changing the ON / OFF DUTY of the switch element while keeping the voltage applied to the LED constant, the ON / OFF frequency of the switch element is high so that the LED light does not flicker. Although it is necessary to set, the ON time of the switch element is shortened at the time of deep dimming (when dark). Especially when dimming near 0%, it is difficult to control the ON time of the switch element with high accuracy, so switching dimming is performed until the ON time of the switch element can be controlled with high accuracy. The ON time of the switch element is constant, and the dimming can be performed in proportion to the dimming signal up to a deeper dimming level by performing dimming by controlling the LED applied voltage.
JP 2003-157986 A

  However, in the conventional LED light control device, when the LED current is large, there is a problem that if the LED current is intermittent, the pulse current generates a large noise. On the other hand, when the current flowing through the LED is a continuous current and dimming is performed by controlling the magnitude of the current, if the current is reduced, the brightness will vary even if the same current is applied due to the variation in the LED elements. There was a problem of coming.

  An object of the present invention is to provide an LED dimming device in which noise hardly occurs even when the LED current is large, and brightness does not easily vary even when the dimming is deepened.

  According to the present invention, in order to solve the above problem, as shown in FIG. 1, current adjusting means (constant current circuit 6) that variably controls the magnitude of the current flowing through the LED load 4, and the LED load 4 A switch means (transistor Q1) for intermittently controlling the flowing current, and a dimming control means (microcomputer 5) for receiving the dimming signal output from the dimmer 1 and controlling the current adjusting means and the switch means. In the LED dimming device, the dimming control means sets the current flowing through the LED load 4 as a continuous current when the dimming signal output from the dimmer 1 is on a higher luminance side than a predetermined level, The LED load 4 is dimmed according to the magnitude of the flowing current, and when the dimming signal output from the dimmer 1 is on the lower luminance side than the predetermined level, the current flowing through the LED load 4 is pulsed. , The average value of the waveform When the LED load 4 is dimmed, the predetermined level is as shown in FIG. 3 when the ratio of the voltage change to the current change in the V-I characteristic of the LED load 4 passes the rated current. It is characterized in that it is set in a range of 3 to 5 times as compared with the above.

  According to the present invention, when the dimming is shallow and bright, the current flowing through the LED load is changed, and when the dimming is deep and dark, the current flowing through the LED load is changed to pulses, and the dimming is performed by the average value of the waveform. Therefore, it is possible to realize an LED light control device that hardly generates noise when the light control is bright, and that does not cause variations in brightness even when the light control is deepened.

(Embodiment 1)
FIG. 1 shows a circuit configuration of Embodiment 1 of the present invention. The present embodiment includes a dimmer 1, a power source 2, an LED lighting device 3, and an LED load 4. The LED lighting device 3 includes a microcomputer 5, a constant current circuit 6, a resistor R1, and a transistor Q1. The constant current circuit 6 is configured to flow a constant current specified by a signal from the microcomputer 5. The microcomputer 5 has a function of reading a dimming signal from the dimmer 1, controlling ON / OFF of the transistor Q 1, and setting a current value of the constant current circuit 6.

  The microcomputer 5 has a predetermined dimming level (a). In a region brighter than the dimming level (a), the transistor Q1 is fixed to ON and the set current of the constant current circuit 6 is changed. Adjust the light with. This is called a DC dimming mode. In a region darker than the dimming level (a), the set current of the constant current circuit 6 is fixed, the transistor Q1 is turned ON / OFF, and the DUTY is changed to perform dimming. This is called a DUTY dimming mode.

  The operation of this embodiment is shown in FIG. 2A shows the relationship between the light control signal output level and the light output, FIG. 2B shows the relationship between the light control signal output level and the LED current (peak value), and FIG. 2C shows the light control signal output. The relationship between the level and the DUTY of the pulse waveform is shown.

  The setting of the dimming level (a) is determined by the VI characteristic of the LED element. It is assumed that the VI characteristic of a certain LED element is as shown in FIG. In the figure, Vf is a forward voltage, and If is a forward current. Let ΔV / ΔI at the rated current be A. As the current flowing through the LED element is lowered, ΔV / ΔI (= B) increases. When the value of B is 3 to 5 times or more than the value of A, the LED element becomes unstable and the variation becomes large, so that the region where this does not occur is set to the DC dimming mode. The light control level (a) is set. In addition, as shown in FIG. 2 (b), when the peak current in the DUTY dimming mode is set to the minimum current in the DC dimming mode, the dimming at the mode switching portion becomes continuous and smooth dimming. Light is possible.

  According to this embodiment, when the dimming level is on the high luminance side, it is lit with a continuous current, so even if the LED current increases, noise is less likely to occur, and when the dimming level is on the low luminance side The LED dimming device is lit with intermittent current, and the peak current is lit at a level where variations in brightness of the elements do not become a problem. It became possible to provide.

  The dimming signal output of the dimmer 1 may be an analog signal (DC 0 V to 10 V, etc.), a DUTY signal (1 KHz, 10 V, etc.), or a digital signal (DMX signal, etc.). It may be. The power source 2 may be either AC or DC. The LED load 4 may be an LED unit constituted by one element or an LED unit constituted by a plurality of LED elements.

  Further, any load that can be lit by a DC power source or a pulsed power source instead of the LED load 4 can be substituted for an arbitrary load, and the same effect can be obtained with an organic EL or the like.

  In the DUTY dimming mode, the current flowing through the LED is a rectangular wave, which is the most effective waveform, and the pulsed waveform is a waveform other than a sine waveform, triangular waveform, or flat DC waveform. If there is, the same effect can be obtained.

(Embodiment 2)
FIG. 4 shows a circuit configuration of the second embodiment of the present invention. The present embodiment includes a dimmer 1, a power source 2, an LED lighting device 3, and an LED load 4. The LED lighting device 3 includes a microcomputer 5, a constant current circuit 6, resistors R1 and R2, and a semiconductor switch element Q1 such as a MOSFET.

  The constant current circuit 6 is configured to flow a specified constant current according to a voltage signal from the microcomputer 5. The microcomputer 5 has a function of reading a dimming signal from the dimmer 1, controlling ON / OFF of the switch element Q 1, and setting a current value of the constant current circuit 6. The dimming signal from the dimmer 1 is a DMX signal that is generally used in lighting, but the DMX signal has a dimming level of 256 levels (1 byte) and dims the LED. Not enough. Therefore, in order to perform smooth dimming, 2 bytes of data are used, numerical data from 0 to 65535 is used as a dimming signal of dimming level, 0 is turned off, and 65535 is turned on 100%.

  Now, when the signal from the dimmer 1 is the maximum value 65535, the microcomputer 5 turns off the switch element Q1 and instructs the constant current circuit 6 to flow the maximum current (for example, 1 A). Then, a current of 1 A flows through the LED load 4. Next, assuming that dimming is reduced to about 50% and 32768 is received as the value of the dimming signal, the microcomputer 5 instructs the constant current circuit 6 to flow a half current of 500 mA, and the light of the LED load 4 Is also about 50%.

  When the dimming is further reduced and the signal of 32767 is received as the value of the dimming signal, the microcomputer 5 sets the current flowing through the constant current circuit 6 to zero and turns on the switch element Q1. In this case, if the resistor R2 is set in advance so that a current of approximately 500 mA flows when the switch element Q1 is turned on, the LED current at this time is 500 mA, and the light of the LED load 4 is also approximately 50%. There is almost no change in light.

  When the dimming is further reduced to half and a signal of 16384 is received as the dimming signal value, when the switch element Q1 is turned ON / OFF and DUTY is 50%, the brightness of the LED load 4 is about 25%.

  When the dimming is further reduced to half and the signal of 8192 is received as the dimming signal value, the brightness of the LED load 4 is reduced to 12.5% by turning on / off the switch element Q1 to DUTY 25%. I can do it.

  At this time, if the repetition frequency for turning on / off the switching element Q1 is low, flickering is caused. Therefore, a repetition frequency of 60 Hz or more is generally required. Further, in order to prevent flicker from occurring during video shooting or the like, it is necessary to blink at a higher frequency (300 Hz or higher).

  On the other hand, if there is no limitation on the capability of the microcomputer 5, the upper limit of the repetition frequency is limited by the response speed of the switch element Q1, and the response speed of the switch element Q1 is assumed to be 10 nsec. Assuming the case, 1 / (10 nsec × (1 / 0.1%)) = 100 kHz is the upper limit of the repetition frequency. However, when the repetition frequency is increased, power loss increases and noise is likely to be generated. Therefore, it is preferable to select a frequency near the lower limit for the repetition frequency. For simplicity, the repetition frequency is set to 1000 Hz as a frequency at which flicker does not occur even in video shooting.

  If the dimming is further narrowed down and the DUTY is 10% (LED light is 5%), the pulse width is 100 μs, and if the DUTY is 1% (LED light is 0.5%), 10 μm A pulse width of seconds is required. When dimming an LED smoothly, dimming of at least about 0.1% is necessary, so the required DUTY is 0.2% (LED light is 0.1%), and the pulse width at that time Becomes 2 μs.

  Usually, when this pulse width is realized by a microcomputer, a high-performance microcomputer, an external circuit, and the like are required, resulting in an increase in cost. Therefore, when the DUTY is 2% (LED light is 1%), if the repetition frequency is lowered by one digit and changed to a low frequency such as 100 Hz, the pulse width becomes 200 μsec, and even if DUTY 0.2%, 20 μ Dimming with a pulse width of seconds is possible.

  The operation of this embodiment is shown in FIGS. 5 shows the relationship between the light control signal output level and the light output, FIG. 6 shows the relationship between the light control signal output level and the LED current (peak value), and FIG. 7 shows the relationship between the light control signal output level and DUTY. Yes.

  Even in this case, if the repetition frequency is set to 60 Hz or more, there is no problem because flicker does not occur in terms of visual feeling. In addition, flickering during video shooting is unavoidable at a low blinking frequency such as 100 Hz, but when used as a light source for video shooting, it is considered to be used in a brightly lit area. This is also not a problem.

  By adopting the above configuration, noise generation is small even when dimming an LED with a large load current, variation in the LED light when dimming deeply can be reduced, and the dimming ratio is increased. It has become possible to provide an LED dimming device capable of smooth dimming.

  In the above description, when the dimming signal is 50%, the DC dimming mode is switched to the DUTY dimming mode, and when the dimming signal is 1%, the repetition frequency of the DUTY dimming mode is switched from 1000 Hz to 100 Hz. However, the dimming level for switching can be changed as appropriate, and the same effect can be obtained by increasing the frequency types and increasing the dimming level for switching the frequency in multiple stages even when changing the repetition frequency. . Further, instead of switching from 1000 Hz to 100 Hz, means (frequency dimming) for dimming by reducing the repetition frequency while fixing the ON pulse width at 1000 Hz may be used.

(Embodiment 3)
FIG. 8 is a circuit diagram showing the overall configuration of Embodiment 3 of the present invention. In the present embodiment, a lighting circuit for the LED load 4 is configured by a flyback DC-DC converter 10 having two feedback control circuits 11 and 12. Hereinafter, the circuit configuration will be described.

  Overvoltage protection elements ZNR are connected in parallel to AC input terminals 21 and 22 connected to a commercial AC power supply (AC 100 V, 50/60 Hz), and an AC input terminal of a diode bridge DB is connected. A smoothing capacitor C1 is connected in parallel to the DC output terminal of the diode bridge DB.

  The smoothing capacitor C1 is connected to the primary winding of the insulating transformer T1 via the output terminal Q-G of the drive circuit 14. The drive circuit 14 has a built-in power MOSFET (not shown) between the output terminals Q and G. By switching between the output terminals Q and G between a short circuit state (ON state) and an open state (OFF state) at high frequency, an isolation transformer is provided. The primary winding of T1 is excited at high frequency. An output capacitor C2 is connected to the secondary winding of the insulating transformer T1 via a rectifying diode D1. The DC-DC converter 10 is configured by the above circuit.

  A series circuit of an LED load 4, a current detection resistor Ra, and a switching element Q1 is connected in parallel to the output capacitor C2. The switching element Q1 is controlled to be turned on / off by the drive circuit 14, and is always turned on during high luminance output, and is turned on / off at a cycle that does not feel to human eyes during low luminance output.

  The current feedback control circuit 11 detects the voltage across the current detection resistor Ra, and feeds back the detected value of the load current to the drive circuit 14 via the feedback control switching means 13.

  The voltage feedback control circuit 12 detects the voltage across the output capacitor C2, and feeds back the detected value of the load voltage to the drive circuit 14 via the feedback control switching means 13.

  The feedback control switching means 13 inputs the detection values of the current feedback control circuit 11 and the voltage feedback control circuit 12 and feeds back the detection value of the current feedback control circuit 11 to the drive circuit 14 at the time of high luminance output, and at the time of low luminance output. The detection value of the voltage feedback control circuit 12 is fed back to the drive circuit 14.

  The drive circuit 14 includes a dimming control unit 15. The dimming control unit 15 variably controls the frequency and ON time width at which the output terminal Q-G of the drive circuit 14 is turned ON / OFF at a high frequency, and does not feel the switching element Q1 to human eyes at the time of low luminance output. A control signal for ON / OFF driving is generated at a certain cycle.

  To the dimming signal input terminals 23 and 24, for example, a dimming signal including a rectangular wave signal having a frequency of 1 kHz and a pulse width of DC 10 V is input. The dimming signal is converted into a voltage signal corresponding to the DUTY of the dimming signal by the signal conversion circuit 16 and input to the dimming control unit 15 and the feedback control switching unit 13.

  The dimming control unit 15 receives the signal obtained by converting the dimming signal into a DC voltage by the signal conversion circuit 16 and the feedback signal from the feedback control switching unit 13, and the feedback signal is an appropriate signal corresponding to the dimming level. Control to reach the level.

  9 shows a specific example of the current feedback control circuit 11, FIG. 10 shows a specific example of the voltage feedback control circuit 12, and FIG. 11 shows a specific example of the feedback control switching means 13.

  The current feedback control circuit 11 in FIG. 9 converts the current flowing through the LED load 4 into a voltage with the resistor Ra, inputs the voltage to the IC 1, and flows the current flowing between the cathode and the anode through the light emitting element of the photocoupler PC1. This is a method of performing feedback control by transmitting to the light receiving element of the photocoupler PC1 shown in FIG.

  The voltage feedback control circuit 12 in FIG. 10 divides the load voltage applied to the LED load 4 and the resistor Ra by the resistors R5 and R6 and applies it to the base of the transistor Tr1, and according to the difference from the Zener voltage of the Zener diode ZD1. Thus, the collector current flowing through the transistor Tr1 is passed through the light emitting element of the photocoupler PC2 and transmitted to the light receiving element of the photocoupler PC2 shown in FIG. 11 to perform feedback control.

  11 receives the feedback signal from the current feedback control circuit 11 shown in FIG. 9 by the photocoupler PC1, and receives the feedback signal from the voltage feedback control circuit 12 shown in FIG. 10 by the photocoupler PC2. Thus, either one of the switching elements Q2 and Q3 is turned on and the other is turned off according to the dimming level, so that one of the light receiving elements (phototransistors) of the photocouplers PC1 and PC2 is fed back to the feedback terminal FB of the drive circuit 14. Is configured to input a feedback signal.

  When the switching element Q2 is ON and the switching element Q3 is OFF, constant current feedback control is performed, and the switching element Q1 is maintained in the ON state. On the contrary, when switching element Q2 is OFF and switching element Q3 is ON, constant voltage feedback control is performed, and dimming control can be performed by DUTY variable control of switching element Q1 under the condition that the output voltage of capacitor C2 is constant. Become. The switching element Q1 is an ON / OFF switch when performing DUTY dimming control.

  The operation of this embodiment will be described with reference to the dimming curve of FIG. FIG. 2 (a) schematically shows the change of the light output with respect to the dimming signal output. When the dimming signal (DUTY ratio) is 100%, the maximum light output is obtained, and when the dimming signal is 0%, the dimming is performed. It shows that it becomes the lower limit. The light output decreases linearly with respect to the dimming DUTY ratio (%). However, there is no particular problem even if the characteristic is not limited to a straight line but has a curve to some extent. A point in the middle of the dimming curve (dimming signal a%, light output b) is used as a control system switching point, and when the output is on the higher luminance side than that point, the switching element Q1 is always in the ON state, The feedback control is applied. Further, when the output is on the lower luminance side than the above point, the voltage feedback control is applied, and the switching element Q1 is driven ON / OFF with a period that is not perceived by human eyes, according to the dimming signal. Thus, DUTY variable control is performed.

  The same control can be applied to the second embodiment (FIGS. 5 to 7), and the voltage feedback control is selected in the dimming region where the switching element Q1 performs the DUTY variable control according to the dimming signal, and the switching element Q1 Current feedback control may be selected in a DC dimming region where dimming is performed by current variable control in the ON state.

  Note that at the point of switching ON / OFF of the switching elements Q2 and Q3, malfunction or flicker may occur depending on the timing at the time of switching. Therefore, either set a range where both the switching elements Q2 and Q3 are turned ON, or When the feedback control switching means 13 in FIG. 8 selects the detection value of the voltage feedback control circuit 12, the dimming control unit 15 refers to the detection value of the current feedback control circuit 11 at the same time to eliminate malfunctions and flickers. Such control can also be performed. As a conceptual diagram, FIG. 12 shows that there may be a range in which constant current control and constant voltage control are performed simultaneously.

  In the present embodiment, the configuration of FIGS. 9 and 10 has been described as the circuit system of the current feedback control circuit 11 and the voltage feedback control circuit 12, but any circuit system that performs constant current control and constant voltage control may be used. There is no particular limitation. The DC-DC converter 10 is not limited to the flyback type, and may be a forward type.

It is a block circuit diagram which shows the structure of Embodiment 1 of this invention. It is a light control characteristic figure which shows operation | movement of Embodiment 1 of this invention. It is a characteristic view which shows the load characteristic of Embodiment 1 of this invention. It is a block circuit diagram which shows the structure of Embodiment 2 of this invention. It is a light control characteristic figure which shows operation | movement of Embodiment 2 of this invention. It is a light control characteristic figure which shows operation | movement of Embodiment 2 of this invention. It is a light control characteristic figure which shows operation | movement of Embodiment 2 of this invention. It is a circuit diagram which shows the whole structure of Embodiment 3 of this invention. It is a circuit diagram which shows the principal part structure of Embodiment 3 of this invention. It is a circuit diagram which shows the principal part structure of Embodiment 3 of this invention. It is a circuit diagram which shows the principal part structure of Embodiment 3 of this invention. It is explanatory drawing which shows operation | movement of Embodiment 3 of this invention.

DESCRIPTION OF SYMBOLS 1 Dimmer 2 Power supply 3 LED lighting device 4 LED load 5 Microcomputer 6 Constant current circuit Q1 Transistor

Claims (1)

Current adjusting means for variably controlling the magnitude of the current flowing through the LED load;
Switch means for intermittently controlling the current flowing through the LED load;
An LED dimming device comprising a dimming control means for receiving the dimming signal output from the dimmer and controlling the current adjusting means and the switch means,
The dimming control means includes
When the dimming signal output from the dimmer is on the higher luminance side than the predetermined level, the current flowing through the LED load is set as a continuous current, and the LED load is dimmed according to the magnitude of the flowing current,
When the dimming signal output from the dimmer is on the lower luminance side than the predetermined level, the LED load is dimmed by changing the average value of the waveform by pulsing the current flowing through the LED load. And
The predetermined level is set to a range in which the ratio of the voltage change to the current change in the V-I characteristic of the LED load is 3 to 5 times that when the rated current is passed. Optical device.

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