JP2006196510A - Dimmer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent flickering even while the brightness of a light source is lowered. <P>SOLUTION: A reference waveform signal generation circuit 8 generates a pulse reference waveform signal having a constant period. A light control dial 10 generates a comparison signal of the same polarity as that of the reference waveform signal and having an absolute value variable between a first maximum value and a second minimum value through operation of a regulation means. A comparator 6 generates a rectangular signal having an output level varying from first state to second state during a period where the absolute value of the reference waveform signal exceeds the absolute value of the comparison signal. Ratio of the second state of the rectangular waveform signal to the constant period is varied by varying the value of the comparison signal, and the rectangular waveform signal is applied to a light emitting diode 2 based on the rectangular waveform signal. Angle at the tip of the reference waveform signal is set close to zero. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light control device that adjusts the brightness of a light emitting device.

  Conventionally, there exist some which are disclosed by patent document 1 in the light-emitting device. In this light emitting device, a triangular wave signal is periodically generated as a reference waveform signal, and this is supplied to the comparator, and a comparison signal whose value can be changed is also supplied to the comparator, and the value of the triangular wave signal is compared. In a period larger than the signal, the comparator generates an output signal that becomes, for example, H level. By changing the value of the comparison signal, the ratio (duty ratio) of one period of the triangular wave signal in the period of H level changes. The drive circuit adjusts the voltage supply period to the light source based on the output signal whose duty ratio changes. Therefore, when the duty ratio is large, the voltage is supplied to the light source over a long period of the one period, and when the duty ratio is small, the voltage is supplied to the light source over a short period of the one period. Thus, by changing the value of the comparison signal, the duty ratio is changed and the brightness of the light source is adjusted.

JP-A-8-241133

  Such a light control device may be used for a display device used in, for example, a ship. In this case, it is necessary to make the brightness as low as possible within a range where the display contents can be visually recognized so that the display device is not too bright at night and does not block the view. For example, in the above technique, the value of the comparison signal is increased so that the duty ratio is decreased. In this case, when the value of the power supply voltage being used varies, the comparison signal and the triangular wave also vary, and the duty ratio varies. As a result, the display may flicker.

  An object of the present invention is to provide a light control device that can reduce flicker even if the brightness is lowered to a level that can be visually recognized.

  In the light control device according to the present invention, the reference waveform signal generating means generates a pulsed reference waveform signal having a fixed period. A comparison signal generating means having a polarity identical to that of the reference waveform signal, a comparison which can be changed between the first value having the maximum absolute value and the second value having the minimum absolute value by operating the adjusting means. Generate a signal. The comparison means generates a rectangular wave signal whose output level changes from the first state to the second state during a period in which the absolute value of the reference waveform signal exceeds the absolute value of the comparison signal. By changing the value of the comparison signal, the ratio of the second state of the rectangular wave signal to the fixed period changes, and a voltage is applied to the light source based on the rectangular wave signal. For example, the period during which the voltage is applied is adjusted based on the rectangular wave signal. The tip angle of the reference waveform signal is set close to zero degrees. For example, the angle formed by the intersection of the rising tangent and the falling tangent at the tip of the reference waveform signal is set close to zero degrees.

  In the light control device configured as described above, the angle of the tip of the reference waveform signal is a value close to zero degrees. Therefore, when the brightness is low enough to be visually recognized, that is, the value of the comparison signal is the first value or this value. When the reference waveform signal exceeds the comparison signal, the period when the reference waveform signal exceeds the comparison signal is shorter than one period of the reference waveform signal. Therefore, even if the value of the tip of the reference waveform signal fluctuates or the value of the comparison signal fluctuates, the change in the ratio of the second state of the rectangular wave signal to the fixed period is small, and the flickering of the light source is also caused. Less.

  The reference waveform signal may have a rising portion and a falling portion. In this case, one of the rising portion and the falling portion is such that the tangent at the change point from the falling portion to the rising portion forms an angle of approximately zero degrees with respect to a reference level, and the other of the rising portion and the falling portion is The tangent line at the change point from the falling portion to the rising portion forms an angle substantially perpendicular to the reference level, and at least one of the rising portion and the falling portion changes in an exponential function. For example, when the rising part rises steeply, the falling part falls gently exponentially, and conversely when the falling part falls steeply, the rising part rises gently exponentially. Note that both the rising and falling portions can be changed exponentially.

  With this configuration, when the brightness is lowered by setting the value of the comparison signal to a small value, one of the rising portion and the falling portion changes gently, so that the second of the rectangular wave signal with respect to the certain period is changed. The state ratio is large, and even if the value of the comparison signal or the value of the tip of the reference waveform signal fluctuates, the light source does not flicker. In addition, even when the value of the comparison signal is changed in order to change the brightness, at least one of the rising and falling portions of the reference waveform signal changes slowly exponentially, so a constant ratio Compared with the case where the reference waveform signal is changed, the viewer feels the change in brightness evenly.

  Further, the reference signal generating means includes a fundamental wave signal for generating a fundamental wave signal having one cycle from the first state and the second state, for example, a square wave signal, and the reference wave signal based on the fundamental wave signal. A waveform shaping circuit for generating a waveform signal. In this case, the waveform shaping circuit includes a charge / discharge circuit having a small charge time constant and a discharge time constant larger than this. When the charge / discharge control circuit responds to the change of the fundamental wave from the first state to the second state, the charge / discharge circuit starts charging according to the charge time constant, and the charge voltage reaches a predetermined value. The charge / discharge circuit is discharged according to the discharge time constant. For example, the charge / discharge circuit may include a capacitor and a resistor. The resistance value of the resistor connected to the capacitor can be reduced to reduce the charging time constant, and the resistance value of the resistor connected to the capacitor can be increased to increase the discharging time constant. The charge / discharge control circuit switches this resistance value.

  With this configuration, the light source is controlled on the basis of a fundamental wave with a small duty ratio error at a constant period, so that variations in brightness are reduced and dimming can be performed to a darker brightness. It should be noted that at the start of discharge, the battery can be discharged quickly with the same time constant as the charge time constant, and can be discharged with the large discharge time constant when the voltage of the capacitor drops to a predetermined value. With this configuration, even when the brightness is reduced or the value of the comparison signal or the value of the tip of the reference waveform signal varies, the change in the ratio of the second state of the rectangular wave signal with respect to the certain period is changed. Even when the brightness is increased, the ratio of the second state of the rectangular wave signal to the constant period is large, and the value of the comparison signal or the reference waveform signal can be reduced. There is no flickering of the light source even if the value of the tip of the light source fluctuates.

  As described above, according to the present invention, it is possible to prevent flickering even in a state where the brightness of the light source is dark enough to visually recognize the display.

  A light control device according to an embodiment of the present invention adjusts the display brightness of a display device used in, for example, a ship, and includes a light emitting element, for example, a light emitting diode 2 as a light source, as shown in FIG. ing. In FIG. 1, only one light emitting diode 2 is shown as a representative, but a large number of light emitting diodes are actually used. A constant DC voltage is supplied to the light emitting diode 2 while its supply period is controlled by the drive circuit 4. This supply period occupies a part of one repeated cycle, and as the ratio of the supply period to this one cycle (duty ratio) increases, the period during which the light emitting diode 2 emits light in one cycle becomes longer. The light emitting diode 2 emits light brightly. The smaller the duty ratio, the shorter the period during which the light emitting diode 2 emits light in one cycle. As a result, the light emitting diode 2 emits light darker.

  The drive circuit 4 performs such control based on a control signal that changes the duty ratio supplied from the outside. For this control signal, for example, a rectangular wave signal generated by the comparator 6 is used. The comparator 6 is supplied with a reference waveform signal from a reference waveform signal generating means, for example, a reference waveform signal generating section 8, and a comparison signal generating means, for example, a comparison signal from a dimming dial 10, and the reference waveform signal is compared. When the signal is smaller than the signal, the first state, for example, L level, and when the reference waveform signal is equal to or higher than the comparison signal, the second state, for example, a rectangular wave signal having H level is generated.

  The reference waveform signal generation unit 8 includes a basic waveform generation circuit 8a and a waveform shaping circuit 8b. As the basic waveform generation circuit 8a, an oscillator that repeatedly generates a rectangular wave signal having a predetermined period T shown in FIG. One period of the rectangular wave signal includes a first state, for example, an L level period, and a second state, for example, an H level period, and the L level period is shorter than the H level period. The waveform shaping circuit 8 b shapes the rectangular wave signal supplied from the basic waveform generation circuit 8 a and supplies the reference waveform signal to the comparator 6. Details of the waveform shaping circuit 8b will be described later.

  The dimming dial 10 supplies, for example, a DC voltage having the same polarity as the reference waveform signal, for example, a positive polarity, to the comparator 6 as a comparison signal. The first value having the smallest value is obtained by operating an operating means (not shown). And a DC voltage of an arbitrary value between the second value having the largest value is supplied to the comparator 6. The DC voltage generated by the dimming dial 10 can be changed steplessly by operating the operating means, or can be changed stepwise.

  As shown in FIG. 2, the waveform shaping circuit 8 b has a charge / discharge circuit 12. The charging / discharging circuit 12 has a capacitor 14, one end of which is connected to a reference potential point, for example, a ground potential point. The other end of the capacitor 14 is connected to one polarity, for example, a positive voltage point + Vcc, through a series circuit of a resistor 16 and self-energizing switching means such as a Zener diode 18 and a resistor 20. The Zener diode 18 is connected such that its cathode is located on the resistor 16 side and its anode is located on the resistor 20 side. The self-biased switching means automatically opens and closes according to the magnitude of the voltage applied between both ends. For example, the Zener diode 18 has a voltage with its cathode side being more positive than the anode side. When the voltage is higher than the zener voltage, it is turned on, and when it is lower than the zener voltage, it is turned off. Of course, the Zener diode 18 conducts in the same manner as a normal diode when the anode side is more positive than the cathode side.

  A series circuit of a resistor 22 and a Zener diode 24 is connected in parallel to a series circuit of a resistor 16 and a Zener diode 18. The Zener diode 24 is connected with a polarity such that the cathode is located on the resistor 22 side and the anode is located on the resistor 20 side. The resistance value of the resistor 16 is set larger than the resistance value of the resistor 22, and the Zener voltage of the Zener diode 22 is set higher than the Zener voltage of the Zener diode 18.

  A connection point between the resistor 20 and the anodes of the Zener diodes 18 and 24 is connected to a ground potential point via a semiconductor switching element, for example, a collector-emitter conductive path of the NPN transistor 26. The semiconductor switching element is turned on when a control signal having a predetermined polarity is supplied to the control electrode. In the case of the NPN transistor 26, the semiconductor switching element is turned on when a positive voltage is supplied to the base electrode.

  Therefore, when the NPN transistor 26 is non-conductive, since a positive voltage is supplied to the anode side of the Zener diodes 18 and 24, the Zener diodes 18 and 24 become conductive, and the parallel resistance values of the resistors 16 and 22 The capacitor 14 is charged according to the charge / discharge time constant determined by the capacitance of the capacitor 14, and the voltage at the other end of the capacitor 14 (the connection point with the resistors 16 and 22) rises with a positive polarity.

  When the NPN transistor 26 is turned on, the voltage at the other end of the capacitor 14 is large, and the voltage across the Zener diodes 18 and 24 is equal to or higher than the respective Zener voltage, so that the conduction is maintained and the capacitor 14 is charged. The charged electric charge is discharged through the resistors 16 and 22, the Zener diodes 18 and 24, and the transistor 26, and the voltage at the other end of the capacitor 14 depends on the parallel resistance value of the resistors 16 and 22 and the capacitance of the capacitor 14. It decreases according to a fixed charge / discharge time constant. Eventually, when the voltage at the other end of the capacitor 14 decreases and becomes lower than the Zener voltage of the Zener diode 22, the Zener diode 24 becomes non-conductive. However, since the Zener voltage of the Zener diode 18 is set to be smaller than the Zener voltage of the Zener diode 24, the Zener diode 18 maintains the conductive state. Therefore, the electric charge of the capacitor 14 is discharged through the resistor 16, the Zener diode 18, and the transistor 26. At this time, the voltage at the other end of the capacitor 14 decreases according to the discharge time constant determined by the capacitance of the capacitor 14 and the resistance value of the resistor 16.

  Here, since the resistance value of the resistor 16 is set to a value larger than the resistance value of the resistor 22, the parallel resistance value of the resistors 16 and 22 is smaller than the resistance value of the resistor 16 alone. . Therefore, the charge / discharge time constant described above is smaller than the discharge time constant described above. That is, the capacitor 14 is charged instantaneously according to the charge / discharge time constant, and the capacitor 14 is also discharged instantaneously according to the charge / discharge time constant until the voltage at the other end decreases to the Zener voltage of the Zener diode 24. When the voltage at the other end of 14 becomes lower than the Zener voltage of the Zener diode 24, the voltage is gradually increased according to the discharge time constant.

  A charge / discharge control circuit 28 that controls conduction and non-conduction of the transistor 26 is provided in the waveform shaping circuit 8b. The charge / discharge control circuit 28 has an SR flip-flop 30. The SR flip-flop 30 has a Q terminal and a / Q terminal, and the / Q terminal is connected to the base of the NPN transistor 26 via the resistor 32. The SR flip-flop 30 has an S terminal and an R terminal. A first state, for example, an H level voltage is supplied to the S terminal, and a second state, for example, an L level voltage is supplied to the R terminal. When supplied, the Q terminal is at the H level and the / Q terminal is at the L level voltage. Conversely, when the L terminal is supplied with the L level voltage and the R terminal is supplied with the H level voltage, the Q terminal is L level, / Q terminal becomes H level voltage. When both the S terminal and the R terminal are at the L level, the voltages at the Q terminal and / Q terminal at that time are maintained as they are.

  In order to supply an H or L level voltage to the S terminal and R terminal of the Philip flop 30, comparators 34 and 36 are provided. The comparator 34 is supplied with the rectangular wave signal shown in FIG. 3A from the basic waveform generating circuit 8a shown in FIG. Further, the voltage across the resistor 38 closest to the ground potential point among the three resistors 38, 40, 42 connected in series between the positive voltage point + Vcc and the ground potential point is also supplied to the comparator 34. Have been supplied. The resistance values of the resistors 38, 40, and 42 are set to be equal values. Thus, the voltage across resistor 38 is + 1/3 Vcc. The value of the H level of the rectangular wave signal from the basic waveform generation circuit 8a is set to be larger than +1/3 Vcc, and the L level is set to be smaller than +1/3 Vcc. Then, the comparator 34 supplies an H level voltage to the S terminal of the flip-flop 30 when the value of the rectangular wave signal from the basic waveform generation circuit 8 a becomes smaller than + 1/3 Vcc.

  A voltage across the capacitor 14 of the charge / discharge circuit 12 is supplied to the comparator 36, and a voltage between the resistors 38 and 40, that is, +2/3 Vcc is supplied. The values of the resistors 16, 20, and 22 are selected so that the voltage across the capacitor 14 becomes +2/3 Vcc or more when charged to the maximum. Then, the comparator 36 supplies an H level output voltage to the R terminal of the flip-flop 30 when the voltage across the capacitor 14 becomes +2/3 Vcc or more.

  Next, the operation of the waveform shaping circuit 8b will be described with reference to FIG. Initially, the Q terminal of the flip-flop is at the L level and the / Q terminal is at the H level, the transistor 26 is turned on, the capacitor 14 is in a discharged state, the comparator 36 supplies the L level voltage to the R terminal, It is assumed that the rectangular wave signal from the waveform generation circuit 8a is at the H level, and the comparator 34 also supplies the L level voltage to the R terminal.

  At time t1, when the rectangular wave signal from the basic waveform generation circuit 8a becomes L level as shown in FIG. 3A, the comparator 34 applies an H level voltage to the S terminal as shown in FIG. Supply. At this time, the comparator 36 supplies an L level voltage to the R terminal, as shown in FIG. Accordingly, the Q terminal of the flip-flop 30 becomes H level and the / Q terminal becomes L level, and the transistor 26 is turned off (non-conducting) as shown in FIG.

  As a result, a charging current flows from the resistor 20 to the capacitor 14 via the Zener diode 18 and the resistor 16, and a charging current flows from the resistor 20 to the capacitor 14 via the Zener diode 24 and the resistor 22. Charging is started, and the charging voltage starts to rise as shown in FIG. This charging is performed in accordance with a time constant determined by the series resistance value of the parallel resistance value of the resistors 16 and 22 and the resistance value of the resistor 20 and the capacitance of the capacitor 14, and the parallel resistance value of the resistance values 16 and 22 is Since it is smaller than the resistance value of the resistor 16 alone, it is smaller than the time constant determined by the resistance values of the resistors 16 and 20 and the capacitance of the capacitor 14, and rises rapidly as indicated by symbol r in FIG.

  Thus, at the time t2 when the voltage of the capacitor 14 is rising, the rectangular wave voltage from the reference waveform generation circuit 8a becomes H level, and the L level voltage is supplied from the comparator 34 to the S terminal. . At this time, since the voltage across the capacitor 14 has not yet exceeded +2/3 Vcc, the comparator 36 supplies an L level voltage to the R terminal. Accordingly, the Q terminal maintains the H level voltage and the / Q terminal maintains the L level voltage, and the transistor 26 maintains the non-conductive state. As a result, charging of the capacitor 14 is maintained.

  At time t3, as shown in FIG. 5E, the voltage across the capacitor 14 becomes +2/3 Vcc, and the comparator 36 supplies the H level voltage to the R terminal. As a result, the Q terminal becomes H level and the / Q terminal becomes L level, and the transistor 26 is turned on (conductive) as shown in FIG.

  As a result, the electric charge charged in the capacitor 14 is discharged through the resistor 16, the Zener diode 18, and the transistor 26, and through the resistor 22, the Zener diode 24, and the transistor 26, and the voltage of the capacitor 14 is reduced. It starts to fall to (e). The discharge time constant at this time is determined by the parallel resistance value of the resistors 16 and 22 and the capacity of the capacitor 14, and is smaller than the discharge time constant determined by the resistance value of the resistor 16 alone and the capacity of the capacitor 14. As shown by the symbol d1 in FIG. (E), the voltage across the capacitor 14 falls rapidly.

  As a result of this discharge, the voltage across the capacitor 14 becomes smaller than +2/3 Vcc, so that the L level voltage is supplied from the comparator 36 to the R terminal at time t4. Accordingly, since both the R terminal and the S terminal are at the L level, the current state is maintained as it is, and the rapid discharge from the capacitor 14 is continued.

  Eventually, the voltage across the capacitor 14 becomes equal to or lower than the Zener voltage of the Zener diode 24 at time t5. As a result, the Zener diode 24 is turned off, and discharging is performed via the resistor 16, the Zener diode 18, and the transistor 2. The discharge time constant at this time is determined by the resistance value of the resistor 16 and the capacitance of the capacitor 14, and the resistance value of the resistor 16 alone is larger than the parallel resistance value of the resistors 16 and 22. When the voltage across the capacitor 14 gradually falls as shown by reference numeral d2 in FIG. 5E and eventually decreases to the Zener voltage of the Zener diode 18, the Zener diode 18 is turned off, and the discharge is stopped. The capacitor 14 maintains the voltage at that time. Thereafter, the rectangular wave signal of the basic waveform generation circuit 8a becomes L level again, and the above-described operation is repeated.

  The voltage across the capacitor 14 thus charged and discharged is supplied to the comparator 6 shown in FIG. 1 as a reference waveform signal from the waveform shaping circuit 8b. The reference waveform signal is set such that the rising charging time constant and the initial discharging time constant of the falling edge are set to be small. Therefore, at the intersection of the rising curve r1 and the falling curve d1 that change from rising to falling, both The peak angle that is the angle formed by the curves r and d1, for example, the angle formed by the tangent of the curve r1 and the tangent of the curve d1 at the intersection is sharp and close to zero degrees.

  Since the reference waveform signal has such a sharp peak angle, there are the following advantages. For example, as shown in FIG. 4, when a normal triangular wave signal is supplied to the comparator 6 as a reference waveform signal, when the DC voltage value is low as a comparison signal from the dimming dial 10, that is, the light emitting diode 2 is When brightly shining, for example, even if the peak voltage value of the triangular wave signal fluctuates due to fluctuations in the power supply voltage, the change in the duty ratio is not so large as shown in FIG. Absent. However, as shown in FIG. 3C, when the value of the DC voltage as the comparison signal from the dimming dial 10 is at or close to the maximum voltage that can be generated by the dimming dial 10, that is, When the light emitting diode 2 is lit dark enough to visually recognize the display, if the value of the peak voltage of the triangular wave signal fluctuates due to fluctuations in the power supply voltage, the duty ratio changes greatly as shown in FIG. Flickering is noticeable. This is due to the gradual peak angle of the triangular wave.

  On the other hand, since the reference waveform signal from the waveform shaping circuit 8b has a sharp peak angle, the reference voltage value as the comparison signal from the dimming dial 10 is the highest voltage or this as shown in FIG. Even if the power supply voltage fluctuates and the peak voltage of the reference waveform signal fluctuates, the change in the duty ratio is not so large, and the light emitting diode 2 does not flicker.

  Further, the falling portion of the reference waveform signal changes exponentially rapidly at the falling portion d1, and falls gently exponentially at the falling portion d2, so that the following advantages are obtained. FIG. 6A shows a case where a triangular wave signal as a reference waveform signal and the comparison voltage from the dimming dial 10 are changed at equal intervals from 1 to 7 steps, and FIG. 6B shows each comparison voltage. The voltage generated by the comparator 6 is shown in FIG. In this case, when the comparison voltage is changed at equal intervals, for example, from the first stage to the seventh stage, the interval at which the comparator 6 generates the voltage also changes at equal intervals, and the period during which the light emitting diode 2 emits light is also equal. Although it changes, it does not look like the brightness has changed at regular intervals due to the sensitivity of the human eye. For example, when the comparison voltage is changed from 1 to 3, it appears that the brightness has changed greatly. When the comparison voltage is changed from 3 to 5, the brightness seems to have changed gradually. When it is changed to 7, the brightness does not seem to have changed.

  On the other hand, FIG. 7A shows a case where the reference waveform signal generated by the waveform shaping circuit 8b and the comparison voltage from the dimming dial 10 are changed at equal intervals from 1 stage to 7 stages. Indicates the voltage generated by the comparator 6 when each comparison voltage is used. In this case, when the comparison voltage is 1 to 4, these voltages substantially cross the portion of the falling curve d1. In the case of the comparison voltages 4 to 7, these voltages substantially cross the portion of the falling curve d2. Therefore, the comparison voltages 1 to 4 are divided into small parts, that is, the period during which the comparator 6 generates the voltage is changed finely instead of at regular intervals, and the comparison voltage 4 to 7 is generated by the comparator 6. The period is greatly changed rather than equally spaced so that the human eye appears to have changed the brightness at evenly spaced intervals.

  In the above embodiment, the reference waveform signal itself is configured so that the rising edge is steep and falls steeply in the initial stage of falling from the peak voltage. For example, in the vicinity of the peak of the triangular wave voltage as shown in FIG. In addition, it is possible to superimpose a steep pulse signal having a peak voltage higher than the peak of the triangular wave voltage and an angle formed by a rising portion and a falling portion at the peak close to zero degrees. In the above embodiment, the falling curve of the reference waveform signal is switched in the middle using the Zener diodes 18 and 24. However, the number of series circuits of Zener diodes and resistors is further increased to increase the reference waveform signal. The shape of the falling curve can be changed. In addition, a normal diode may be used in place of the Zener diode 24, charging may be performed quickly by the diode and the Zener diode 18, and discharging may be performed only by the Zener diode 18. Alternatively, a normal diode may be provided in parallel with the Zener diodes 18 and 24, charging may be performed rapidly by the Zener diodes 18 and 24, and the normal diode, and discharging may be performed slowly by the Zener diodes 18 and 24. Moreover, although the values of the resistors 38, 40, and 42 are equal, they may be different from each other.

It is a block diagram of the light modulation apparatus of one Embodiment of this invention. It is a circuit diagram of the waveform shaping circuit of the light modulation apparatus of FIG. It is operation | movement explanatory drawing of the waveform shaping circuit of FIG. FIG. 7 is an operation explanatory diagram of each unit when the value of the comparison voltage is increased when a triangular wave signal is used as a reference waveform signal in the light control device of FIG. 1. FIG. 3 is an operation explanatory diagram of each unit when the value of the comparison voltage is increased in the light control device of FIG. 1. FIG. 3 is an operation explanatory diagram of each unit when a triangular wave signal is used as a reference waveform signal and the comparison voltage is changed at equal intervals in the light control device of FIG. 1. FIG. 2 is an operation explanatory diagram of each unit when a comparison voltage is changed at equal intervals in the light control device of FIG. 1.

Explanation of symbols

2 Light emitting diode (light source)
4 drive circuit 6 comparator 8 reference waveform generation circuit (reference waveform signal generation means)
10 Dimming dial (Comparison voltage generator)

Claims (3)

A reference waveform signal generating means for generating a pulsed reference waveform signal having a constant period;
Comparison that generates a comparison signal having the same polarity as the reference waveform signal, and that can be changed by operating the adjusting means between a first value having the maximum absolute value and a second value having the minimum absolute value. Signal generating means;
Comparison means for generating a rectangular wave signal whose output level changes from the first state to the second state in a period in which the absolute value of the reference waveform signal exceeds the absolute value of the comparison signal,
A dimming device that changes a ratio of the second state of the rectangular wave signal to the fixed period by changing a value of the comparison signal, and applies a voltage to a light source based on the rectangular wave signal;
A dimming device characterized in that the angle of the tip of the reference waveform signal is set close to zero degrees.   2. The light control device according to claim 1, wherein the reference waveform signal has a rising portion and a falling portion, and one of the rising portion and the falling portion is at a change point from the falling portion to the rising portion. The tangent makes an angle of approximately zero degrees with respect to the reference level, and the other of the rising part and the falling part has an angle substantially perpendicular to the reference level at the change point from the falling part to the rising part. A light control device in which at least one of the rising portion and the falling portion changes in an exponential function. 3. The dimming device according to claim 2, wherein the reference signal generating means is based on the fundamental wave signal and a fundamental wave generating circuit that generates a fundamental wave signal having one cycle from the first state and the second state. A waveform shaping circuit for generating the reference waveform signal
The waveform shaping circuit includes a charging / discharging circuit having a small charging time constant and a discharging time constant larger than the charging time constant, and the charging in response to a change of the fundamental wave from the first state to the second state. A light control circuit comprising: a charge / discharge control circuit that causes the charge / discharge circuit to start charging according to a time constant and discharges the charge / discharge circuit according to the discharge time constant when the charge voltage reaches a predetermined value.

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