JP4943892B2 - Light control device and lighting fixture using the same - Google Patents

Description

  The present invention relates to a dimming device that dims an LED and a lighting fixture using the same.

  In a conventional light control device, as a light source for obtaining illumination light, a technique for producing white color by mixing a plurality of LEDs has been performed by, for example, mixing red, green, and blue, or mixing blue with a yellow phosphor. It was. For such LED brightness control, PWM (Pulse Width Modulation) control that mainly controls the temporal duty of current is used. However, the PWM control light control device is difficult to finely control because the duty needs to be narrowed when the current value of the LED is small, the illumination light becomes a color different from the color to be controlled, or the response time of the LED is conventional Since it is shorter than the lamp, it may appear to flicker when the duty in the PWM control falls below a certain value. In general, since an LED is an element having a high luminance, when time-division control such as PWM control is performed, flicker tends to be conspicuous at the lower limit of dimming when PWM control has a low frequency. For this reason, in order to increase the resolution by performing fine control by PWM control with high frequency, it is necessary to select an expensive microcomputer with high frequency and high reliability, resulting in an increase in cost.

  By the way, as shown in Patent Document 1, the dimming ratio of the dimming signal included in the power source input to the input circuit is determined. When the dimming ratio is higher than a predetermined value, PWM control is performed. An LED illumination device is known that expands the adjustment range below a predetermined value by performing peak value control when the value is low. However, in this device, flicker may be seen due to the effect of the remaining PWM control because the control is performed by adding the crest value control to the PWM control by the PWM signal having a small dimming ratio below a predetermined value. In addition, a large peak value is required to suppress this flicker.

  In addition, as disclosed in Patent Document 2, in a lighting device including a lighting circuit for lighting an output from a dimmer with an LED, the lighting circuit includes an output transformer in which a switch element and an LED are connected to the input and output sides, respectively. And detecting circuit and control circuit, detecting the magnitude of the output value of the dimmer and the predetermined value, and detecting that the output value of the dimmer is lower than the predetermined value, the operation of the switch element There is known a lighting device that controls to stop or reduce the output of an output transformer. However, since this apparatus performs PWM control based on phase control and performs PWM control at a frequency of about 50 Hz to 60 Hz, flicker becomes conspicuous when the dimming lower limit is reached. For this reason, when the output of the dimmer becomes equal to or less than a predetermined value, the LED output is stopped in order to prevent flickering malfunction, so that the dimming range is narrowed and the adjustment function is impaired.

Further, as disclosed in Patent Document 3, a constant current circuit that drives an illumination light source with a constant current, a constant current switching circuit that switches a constant current value of the constant current circuit, and an illumination light source according to a duty of a PWM signal 2. Description of the Related Art An illumination dimming device including a PWM drive circuit that is controlled in a known manner is known. However, in this device, by changing the current value of the constant current circuit in several stages, the same PWM control gives a change in brightness due to the difference in the current value and widens the adjustment range, but when the current value is small Since the PWM control is basically performed, flickering occurs when the duty falls below a predetermined value.
JP 2005-267999 A JP 2005-11739 A JP 2005-332586 A

  The present invention has been made to solve the above-described problem. In a dimming device that controls the output of an LED by combining PWM control and analog control, a phenomenon such as flickering occurs near the lower limit of dimming of the LED. It is an object of the present invention to provide a light control device capable of performing smooth light control without generation of low cost.

In order to achieve the above object, a first aspect of the present invention provides a dimming device that controls the output of an LED by combining PWM control and analog control, and provides a dimming signal comprising a PWM signal for controlling the output of the LED. A dimming control unit for generating, a constant current driving unit for driving the LED with a constant current, an analog current control unit for analog controlling the current of the constant current driving unit, and a constant current of the LED by the constant current driving unit A PWM current control unit that controls a drive period according to the duty of the PWM signal, and a PWM current control unit of the LED according to a comparison result between the duty of the PWM signal and a predetermined value set in advance. with a PWM control, and a switching unit for switching the analog control by the analog current controller, wherein the LED, the constant current driver and PWM current Connected control unit in series, the front Symbol switching unit, wherein when the duty of the PWM signal becomes a predetermined value or less, to form an analog control signal by generating a DC voltage corresponding to the duty, the analog control signal the feed to the analog current controller switches the control of the output of the previous SL LED analog control only by the analog current control section,
The analog current control unit inputs a DC voltage of the output to the constant current driving unit, and performs analog control of the LED current with a DC analog current based on the analog control signal .

  According to a second aspect of the present invention, the light control device according to the first aspect is provided.

  According to the first aspect of the present invention, for example, by setting the predetermined value to the duty value of the PWM signal at which flickering starts to occur, the LED current control is performed by the PWM control unit in the vicinity of the dimming lower limit that darkens the LED. Therefore, it is possible to switch only to analog control by the current adjustment unit. Thereby, in dimming near the dimming lower limit for controlling by reducing the current of the LED, dimming can be performed only by analog control, so that the LED can be smoothly controlled without causing a phenomenon such as flickering. A low-frequency microcomputer can be used, and the cost can be reduced.

  According to the invention of claim 2, since the LED can be configured using a dimming device capable of dimming only by analog control in the vicinity of the dimming lower limit, it is possible to realize lighting control with less flicker even when the illumination is darkened. Can do.

  Hereinafter, a light control device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a block configuration of the light control device of this embodiment. This dimming device includes an LED 1, a constant current circuit (constant current drive unit) 2, a PWM current control circuit (PWM current control unit) 3, a current adjustment circuit (analog current control unit) 4, and a dimming control circuit (dimming control). Section) 5, a duty determination circuit (switching section) 6, and a constant voltage power supply circuit 7.

  LED1 is an illumination light source including a plurality of light emitting diodes D1 to D4. The constant current circuit 2 is a power supply circuit that drives the LED 1 at a constant current, and is driven by the voltage output from the current adjustment circuit 4 to flow an output current to the LED 1.

  The PWM current control circuit 3 includes a switching semiconductor element FETQ1 connected between the LED1 and the ground, and the FETQ1 is turned on according to the on-duty (hereinafter referred to as duty) of the PWM signal during the period in which the LED1 is driven at a constant current. The output current I of the LED 1 is PWM controlled by turning off.

  The current adjustment circuit 4 outputs an analog control voltage for controlling the constant current value of the constant current circuit 2 based on an analog control signal C from the duty determination circuit 6 described later, and this analog control voltage is input to the constant current circuit 2. As the voltage Va, the current of the constant current circuit 2 is controlled substantially in proportion to the voltage level of the input voltage Va, and the current of the LED 1 is controlled in an analog manner. As shown in FIG. 2, the relationship between the input voltage Va and the output current I of the LED 1 is that the input voltage Va when the PWM signal is on-duty 100% and the on-duty value Dr (see FIG. 5) is V1. , V2, the output currents at that time are I1 and I2.

  The dimming control circuit 5 outputs a PWM signal with a duty Da as a dimming signal and transmits it to the duty determination circuit 6 as shown in FIG. 3 in response to a user's dimming level instruction. The duty of the PWM signal is changed in proportion to the dimming level under a certain period. When the light control level is high, the duty is increased. When the light control level is low, the duty is decreased.

  The duty determination circuit 6 receives the PWM signal A as the dimming signal on the input side, and outputs the PWM signal B for controlling the PWM current control circuit 3 and the analog control signal C for controlling the current adjustment circuit 4 from the output side. The duty determination circuit 6 stores a predetermined duty value Dr in advance, determines the duty of the PWM signal from the dimming control circuit 5, compares the duty of the PWM signal with the predetermined value Dr, Based on the comparison result, the PWM current control circuit 3 and the current adjustment circuit 4 are controlled, and the current value of the LED 1 is subjected to PWM control and analog control, respectively. The constant voltage power supply circuit 7 is a power supply circuit that supplies a constant voltage Vcc to the constant current circuit 2 for lighting the LED.

  The operation of the present embodiment having the above circuit configuration will be described with reference to FIGS. 4 (a) to 4 (d) and FIG. 4 (a), 4 (b), 4 (c), and 4 (d) are respectively input to the duty determination circuit 6 when the duty is larger than the predetermined value Dr and when the duty is less than or equal to the predetermined value Dr. PWM signals A1 and A2, and the respective duty waveforms of the PWM signals B1 and B2 output from the duty determination circuit 6 to the PWM current control circuit 3 corresponding to the respective inputs of the PWM signals A1 and A2. . FIG. 5 shows the duty (%) when the duty of the PWM signal input from the dimming control circuit 5 is greater than a predetermined value Dr (referred to as P region) and less than or equal to the predetermined value Dr (referred to as Q region). ) Shows a change in the output voltage of the current adjustment circuit 4 (the input voltage Va of the constant current circuit 2) controlled based on the above.

  In the configuration of the present embodiment, the LED 1 is connected in series with the constant current circuit 2 and the PWM current control circuit 3, and the current of the LED 1 flows through the analog current flowing through the constant current circuit 2 and the PWM current control circuit 3. Controlled by both PWM currents.

  The dimming control circuit 5 compares the duty Da of the PWM signal A1 with a predetermined value Dr when the dimming signal is transmitted as the PWM signal A1 according to the user's dimming level instruction. At this time, the predetermined value Dr is set to a level larger than the duty at which the flickering is detected in the illumination brightness in the LED 1 (flicker is not detected), and the duty Da of the PWM signal A1 is greater than the predetermined value Dr as shown in FIG. When it is large, the duty judgment circuit 6 has, as one output signal thereof, as shown in FIG. 4C, a PWM signal B1 having the same duty Da as the input PWM signal A1 (in this case, the same as the PWM signal A1). Is input to the PMW current control circuit 3, and the FET Ql is PWM controlled by the duty Da of the PWM signal B1. At the same time, the duty determination circuit 6 outputs a DC analog control signal C to the current adjustment circuit 4 as the other output signal. In response to the analog control signal C, the current adjustment circuit 4 generates an input voltage V1 to the constant current circuit 2 to control the constant current circuit 2, and causes the constant current I1 to flow through the LED 1. Thus, when the duty in the PWM signal of the dimming signal is larger than the predetermined value Dr (P region shown in FIG. 5), the duty determination circuit 6 determines the time during which the constant current I1 flows through the LED 1 as the PWM signal of the dimming signal. PWM control of the PMW current control circuit 3 is performed at A1, and the dimming level of the LED 1 is controlled by the duty Da of the PWM signal B1 (A1).

  Next, when the user reduces the dimming level in the dimming control circuit 5, and the duty Da of the PWM signal A2 of the dimming signal becomes less than the predetermined value Dr as shown in FIG. As shown in FIG. 4 (d), the duty determination circuit 6 sets the duty of the PWM signal B2 to the FET Ql of the PMW current control circuit 3 to 100% and generates a DC voltage corresponding to the duty Da of the PWM signal A2. The analog control signal C is generated and sent to the current adjustment circuit 4, and the DC voltage V <b> 2 is output from the current adjustment circuit 4 and applied to the input of the constant current circuit 2. The constant current circuit 2 outputs a current I2 to the LED 1 when the DC voltage V2 is input as the input voltage Va. Here, the current I2 is controlled to be equal to the current Il × Dr (%), whereby the current I2 is a direct current value proportional to the magnitude of the duty Da of the PWM signal A2 of the dimming signal. It is controlled to become. Thereafter, when the duty is further reduced (Q region in FIG. 5), the duty determination circuit 6 reduces the voltage output to the current adjustment circuit 4 in accordance with the magnitude of the duty Da, and the constant current circuit 2 In response to this, the value of the current flowing through the LED 1 is reduced. As a result, the current output to the LED 1 is PWM-controlled by the PWM signal at a dimming level where the duty is greater than the predetermined value Dr (the output level of the LED 1), and at a dimming level below the predetermined value Dr, it is an analog current. Analog control is performed.

  FIG. 6 shows a state of relative current change of the LED 1 in switching between PWM control and analog control of the LED 1 based on the duty determination of the duty determination circuit 6. FIG. 6A shows a case where the current I of the LED 1 is PWM-controlled over the entire adjustment range, and as shown in the D section, even when the duty is equal to or less than a predetermined value Dr, it changes in a stepwise manner in a non-linear manner. So you can see the flicker. FIG. 6B shows the relative current change of the analog control by the current adjustment circuit 4 only when it is less than the predetermined value Dr. FIG. 6C shows that the current I of the LED 1 is PWM-controlled by the PWM current control circuit 3 when the duty of the PWM signal is larger than the predetermined value Dr, and the PWM current when the current I is less than the predetermined value Dr shown in the E section. A relative change in the current I of the LED 1 corresponding to the duty when analog control is performed by switching from the control circuit 3 only to the current adjustment circuit 4 is shown. As can be seen from the comparison between the D portion in FIG. 6A and the E portion in FIG. 6C, in the region where the duty is lower than the predetermined value Dr (Q region), the control is switched from PWM control to analog control. Thus, the current I of the LED 1 can be smoothly controlled even in a region where the dimming level is low.

  As described above, according to the light control device 1 of the first embodiment, by setting the predetermined value Dr to a duty value at which flickering starts to occur, when the duty of the light control signal is greater than the predetermined value Dr, the LED 1 PWM drive is performed by the PWM current control circuit 3, and when the duty of the dimming signal is equal to or less than the predetermined value Dr, the PWM current control circuit 3 is PWM controlled with a constant duty substantially 100% sufficiently larger than the predetermined value Dr, thereby performing PWM control. The constant current circuit 2 can be controlled with a DC voltage having a magnitude proportional to the duty of the dimming signal, and the current of the LED 1 can be controlled in an analog manner only by analog control by the current adjustment circuit 4. As a result, it is possible to prevent a phenomenon such as LED flickering from occurring even in the vicinity of the dimming lower limit that requires a small current control. Further, in the PWM current control circuit 3, for the dimming lower limit adjustment, the duty is reduced too much so that the switching element of the FET Ql is not operated in the minimum control time or less, and smooth control up to the dimming lower limit is performed only by analog control. It can be carried out. Furthermore, since a high-frequency microcomputer is not required, it can be manufactured at low cost. Even if the duty of the PWM signal to the FET Ql in the PWM current control circuit 3 is not 100%, the same effect can be obtained as long as it is larger than the predetermined value Dr. The constant current circuit 2 does not have to be proportional to the voltage.

  Next, a light control device according to a second embodiment of the present invention will be described with reference to the drawings. Since the configuration of this embodiment is the same as that of the above embodiment, a description thereof will be omitted. In the light control device according to the present embodiment, in the P region where the duty is larger than the predetermined value Dr (see FIG. 5), when light control is performed in the middle of each duty of the PWM signals of the two light control signals, the duty is large. Unlike the first embodiment, the other points are the same in that the PWM control is performed on the other side and the current value is brought between the two by analog control.

  As shown in FIGS. 7 and 8, in the P region, the section in which the output current I flowing through the LED 1 is Il (current value when the duty is 100%) is controlled by the PWM duty, and the dimming level changes. At this time, when the duty changes digitally, the current value also changes stepwise. When the duty in the PWM signal of the dimming signal is Da, Db, the current value flowing through the LED 1 is Ia = Il × Da ( %), Ib = Il × Db (%).

  Here, when the user wants to dim the current value I of the LED 1 with a current value Ic at a level intermediate between Ia and Ib, the dimming control circuit 5 (see FIG. 1), as shown in FIG. The PWM signal A input to the duty determination circuit 6 is alternately output as the PWM signal of the period T, and the duty Da and the duty Db can be effectively obtained to obtain a current value Ic at an intermediate level between Ia and Ib. . However, when the difference between the duty Db and the duty Db is large, the LED 1 may detect flicker.

  On the other hand, when the PWM signal A having the duties Da and Db is input, the duty determination circuit 6 stores these values Da and Db in a storage unit (not shown) in the duty determination circuit 6. Then, as shown in FIG. 9B, the duty Db of the larger Da, Db stored (here, Db> Da) is made constant and the PWM signal B of the duty Db is output, and the PWM signal The PWM current control circuit 3 is controlled by B. Then, as shown in FIG. 8, the duty determination circuit 6 controls the current adjustment circuit 4 while controlling the current value I of the LED 1 to be larger than Ia by controlling the PWM current control circuit 3 with the duty Db. Adjustment is made so that the current value I is at the intermediate Ac point (current value Ic) between the Ab point (current value Ib) corresponding to the duty Db on the current value I and the Aa point (current value Ia) corresponding to the duty Da. To do. As a result, in the intermediate adjustment between the duties Da and Db, the light between Ia and Ib can be dimmed by analog control. Therefore, when the difference between the duties Da and Db is large, the flickering of the LED 1 can be suppressed and smooth. Dimming can be performed. Further, since the PWM control of the PWM current control circuit 3 is performed with the larger duty of Da and Db, flickering due to PWM control can be further suppressed.

  As described above, according to the dimming device 1 of the second embodiment, the dimming level between the current values Ia and Ib is effectively achieved by the PWM control in which the duty Da and the duty Db are alternately applied to the PWM current control circuit 3. As compared with the case where the current value Ib is obtained, the flicker that occurs when the difference between the current value Ia and the current value Ib becomes large when the duty cycle T is large or when the microcomputer is controlled with a low resolution can be reduced. As a result, since the duty is not changed frequently, fine control can be realized at low cost while reducing flicker.

  As described above, according to the various embodiments, flickering can be suppressed by making the current control of the LED 1 only analog control by the current adjustment circuit 4 in the vicinity of the dimming lower limit of the LED 1, but brighter than the dimming lower limit. In the dimming of the area, flicker can be reduced by combining low-frequency and low-resolution microcomputers by combining PWM control with a large duty and analog control. Thereby, a low-cost light control device that can suppress flickering over the entire area of light control can be formed, and a lighting device with less flickering can be realized using this light control device.

  The present invention is not limited to the configuration of each of the above embodiments, and various modifications can be made. For example, the duty of the PWM signal applied to the PWM current control circuit is set to 100% when the value is equal to or less than a predetermined value. However, the duty is not necessarily 100%, and the duty range is larger than the predetermined value and does not cause flickering. It may be 100% or less. Further, the arrangement of the switching transistors of the constant current circuit, the LED, and the PWM current control circuit is not limited as long as they are connected in series.

The block block diagram of the light modulation apparatus which concerns on the 1st Embodiment of this invention. The figure which shows the characteristic of the constant current circuit of an apparatus same as the above. The figure which shows the waveform of the PWM signal of an apparatus same as the above. (A), (b) is a figure which shows the waveform of the PWM signal in the input side of the duty determination circuit of an apparatus same as the above, (c), (d) is a figure which shows the waveform of the PWM signal in the output side of the duty determination circuit. The figure which shows the operating characteristic of the duty determination circuit of an apparatus same as the above. The figure which shows the output characteristic of LED of an apparatus same as the above. The figure which shows the output characteristic of LED of the light modulation apparatus which concerns on the 2nd Embodiment of this invention. The figure which shows the operating characteristic of the duty determination circuit of an apparatus same as the above. (A) is a figure which shows the input waveform of the PWM signal to the duty determination circuit, (b) is a figure which shows the output waveform of the PWM signal from the duty determination circuit of the same apparatus.

Explanation of symbols

1 LED
2 Constant current circuit (constant current drive unit)
3 PWM current control circuit (PWM current control unit)
4 Current adjustment circuit (analog current controller)
5 Dimming control circuit (Dimming control unit)
6 Duty judgment circuit (switching part)

Claims (2)

In the dimming device that controls the output of the LED by combining PWM control and analog control,
A dimming control unit that generates a dimming signal including a PWM signal for controlling the output of the LED;
A constant current drive unit for driving the LED with a constant current;
An analog current control unit for analog control of the current of the constant current drive unit;
A PWM current control unit that performs current control according to the duty of the PWM signal during a constant current drive period of the LED by the constant current drive unit;
In accordance with a comparison result between the duty of the PWM signal and a predetermined value set in advance, the PWM control by the PWM current control unit of the LED, and a switching unit for switching analog control by the analog current control unit ,
The LED is connected in series with the constant current drive unit and the PWM current control unit,
Before SL switching unit, when the duty of the PWM signal becomes a predetermined value or less, to form an analog control signal by generating a DC voltage corresponding to the duty, the analog control signal to the analog current controller feed, switching control of the output of the previous SL LED only analog control by the analog current controller,
The dimming device according to claim 1, wherein the analog current control unit inputs the output DC voltage to the constant current driving unit, and analog-controls the LED current with a DC analog current based on the analog control signal .   A lighting fixture comprising the light control device according to claim 1.

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