JP2011228063A - Light-emitting diode drive dimmer circuit, light-emitting diode illumination device, light-emitting diode backlight device, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting diode drive dimmer circuit capable of modulating light over a wide range, a light-emitting diode illumination device, a light-emitting diode backlight device, and a liquid crystal display device.SOLUTION: An output voltage V1 applied to an LED row 9 is divided while the LED row 9 is turned on, with the result retained as a comparison reference voltage, and constant voltage control is exercised based on the comparison reference voltage while the LED row 9 is turned off, with the output voltage V1 referenced as constant voltage. Thus, a voltage during a turn-on period T1 during which the LED row 9 was turned on can be applied to the LED row 9 when it turns on again. That way, a delay time until a current IF flowing in the LED row 9 reaches a set current IF' can be minimized. Therefore, even when a duty cycle of a dimmer PWM signal is reduced, an LED drive dimmer circuit 1 can be maintained operative while the current IF flowing in the LED row 9 is in the sate of the set current IF'.

Description

  The present invention relates to a light-emitting diode drive dimming circuit, a light-emitting diode backlight device, and a liquid crystal display device that modulate the pulse current of a current flowing through the light-emitting diode row to adjust the brightness of the light-emitting diode row.

  LED (Light Emitting Diode) light sources used in LCD backlights and lighting equipment are more energy-saving, longer life, and mercury-free than conventional cold-cathode fluorescent lamps (CCFLs) In addition, the brightness can be easily changed, that is, the light control is easy.

  For the LED light source, a PWM (Pulse Width Modulation) control circuit is well known as a circuit for adjusting (dimming) the brightness of the LED.

  FIG. 10 is a circuit diagram of a conventional PWM control circuit 101. In FIG. 10, a PWM control circuit 101 includes a DC power source 102, a DC / DC converter 103, an LED string 104 (load) in which one or a plurality of LEDs are connected in series, and a sensor that measures a current flowing through the LED string 104. A resistor R101 is provided. The DC power source 102 supplies the input voltage Vin to the DC / DC converter 103. The voltage across the LED array 104 is VF.

  Note that a voltage obtained by rectifying an AC voltage output from an AC power supply different from the DC power supply 102 may be supplied to the DC / DC converter 103 as the input voltage Vin.

  A control IC 105 included in the DC / DC converter 103 controls ON / OFF of the switching element Q101. Thereby, the voltage value of the output voltage V101 of the DC / DC converter 103 is changed by changing the switching frequency of the switching element Q101 or the pulse width (switching pulse width) of the switching pulse output from the switching element Q101. .

  The conventional PWM control circuit 101 of FIG. 10 further includes a constant current feedback circuit 106, and a dimming PWM signal (rectangular wave) is input to the constant current feedback circuit 106. The constant current feedback circuit 106 includes an operational amplifier IC101, transistors Q102 and Q103, and resistors R102 to R108.

  The constant current feedback circuit 106 oscillates the switching element Q101 only during the ON period of the dimming PWM signal (rectangular wave). A rectangular wave voltage Va is obtained from the input voltage Vin by turning on / off the switching element Q101. The rectangular wave voltage Va is smoothed by the smoothing capacitor C101 to obtain a voltage V101 (output voltage of the DC / DC converter 103).

  The DC / DC converter 103 is a step-up chopper regulator having a choke coil L101. Therefore, the output voltage V101 of the DC / DC converter 103 can be made higher than the input voltage Vin. In the PWM control circuit 101, the oscillation frequency of the switching element Q101 or the switching pulse width is controlled to control the voltage V101 so that the output of the sensor resistor R101 is constant, and the current IF flowing through the LED array 104 is made constant. Yes (constant current feedback operation).

  The member indicated by reference numeral D101 in FIG. 10 is a backflow prevention diode, and prevents the charge (charge) stored in the smoothing capacitor C101 from returning to the DC power source 102 side.

  In PWM control, the ratio of the time during which the current IF is supplied to the LED is controlled. The PWM control circuit 101 in FIG. 10 controls the brightness of the LED array 104 by changing the duty ratio of the dimming PWM signal that is a pulse (the ratio of the period during which the pulse is Hi in one cycle). .

  The switching frequency of the switching element Q101 included in the DC / DC converter 103 is within a range of several tens of kHz to 100 kHz (within the same range as a normal DC / DC converter).

  On the other hand, the frequency of the dimming PWM signal is in the range of 100 Hz to 500 Hz. Hereinafter, “frequency” means “frequency of dimming PWM signal”. If the frequency of the dimming PWM signal is lower than 100 Hz, the blinking of the LEDs in the LED row 104 is visually recognized. On the contrary, when the frequency of the dimming PWM signal is higher than 500 Hz, the ON time of the dimming MIN (ON time when the brightness of the LED row 104 is the darkest) becomes constant. For this reason, if the frequency is too high, the dimming range cannot be widened as a result.

  For example, it is assumed that the ON time during dimming MIN is shortened only to ton = 0.2 mS. When the frequency of the dimming PWM signal is 500 Hz, the cycle of the dimming PWM signal is Tc = 2 mS, and ton / Tc = 10%. Further, when the frequency of the dimming PWM signal is 1 kHz, the cycle Tc = 1 mS of the dimming PWM signal and ton / Tc = 20%. Comparing the former and the latter, the latter having a higher frequency of the dimming PWM signal has a smaller dimming width.

  The emission wavelength of the LED varies depending on the peak value of the current flowing through the LED. For this reason, by using PWM modulation to drive the LED, the amount of current flowing through the LED is changed without changing the peak value of the current flowing through the LED. The brightness of the LED is determined by the amount of current flowing through the LED, and the brightness is increased as the duty ratio of the dimming PWM signal is increased.

  In PWM control, it is generally ideal that the brightness of the LED can be controlled linearly when the duty ratio of the dimming PWM signal is between 0% and 100%. In the dimming operation of the LED using the PWM control, a function of adjusting (dimming) the brightness of the LED according to the duty ratio of the dimming PWM signal is required.

  In the PWM control circuit 101 of FIG. 10, the magnitude of the current IF flowing through the LED is measured by the sensor resistance R1. In the PWM control circuit 101, the control IC 105 controls the current IF by changing the switching frequency or switching pulse width of the switching element Q101.

  A period in which the dimming PWM signal is Hi is an LED lighting period, and a period in which the dimming PWM signal is LOW is an LED extinguishing period.

(Lighting period)
Since the dimming PWM signal is Hi, the base potential of the transistor Q103 becomes Hi, and the transistor Q103 is turned ON. As a result, the emitter and base of the transistor Q103 are electrically grounded, and the potential of the base of the transistor Q102 becomes LOW, so that the transistor Q102 is turned OFF.

  Since the transistor Q102 is turned off, the operational amplifier IC101 compares the reference voltage Vref divided by the resistors R102 and R103 with the voltage across the sensor resistor R101 through which the current IF flowing through the LED flows, and according to the comparison result. Thus, by increasing / decreasing the voltage V101 applied to the LED, the current IF flowing to the LED is made constant (set current IF ′, see FIG. 11A) (that is, constant current feedback operation is performed). ).

(Light-out period)
Since the dimming PWM signal is LOW, the base potential of the transistor Q103 becomes LOW, and the transistor Q103 is turned OFF. As a result, the emitter-base of the transistor Q103 is opened and the base potential of the transistor Q102 becomes Hi, so that the transistor Q102 is turned on.

  Since the transistor Q102 is turned on, the reference voltage obtained by dividing the reference voltage Vref by the resistors R102 and R103 becomes 0V. Therefore, the operational amplifier IC101 sets the current IF flowing through the LED to 0, that is, stops the DC / DC converter 103 from supplying the voltage V101.

  Here, similarly to the PWM control circuit 101 in FIG. 10, the embodiment 3 of Patent Document 1 includes both the current feedback control circuit 11 and the voltage feedback control circuit 12 as having a dimming function of the LED. An LED dimming device is disclosed. At high luminance, the voltage is increased or decreased in constant voltage control to control the brightness of the LED (the amount of current flowing through the LED). At low luminance, the brightness (current amount) of the LED is controlled by constant current control (PWM control).

  Next, the invention according to Patent Document 2 discloses an IC that controls the luminance of an LED by a PWM method using an external constant voltage power source. The N-channel field effect transistor N1 in FIG. 4 of Patent Document 2 corresponds to the switching element Q101 in FIG.

  Further, Patent Document 3 discloses a light emission control circuit using the PWM control circuit 101 of FIG.

  And in patent document 4, the LED drive circuit which can send the equal electric current to the some LED circuit paralleled is disclosed.

JP 2009-123681 A (released on June 4, 2009) JP 2009-33090 A (published February 12, 2009) JP 2005-93566 A (published April 7, 2005) JP 2006-319221 A (published on November 24, 2006)

  FIG. 11A is a waveform diagram showing each waveform in the PWM control circuit 101 of FIG. In FIG. 11A, the waveform indicated by the solid line is a waveform when the period during which the dimming PWM signal is ON is longer, and the waveform indicated by the broken line is when the period during which the dimming PWM signal is ON is shorter. It is a waveform. FIG. 11B is a graph showing the VF-IF characteristics of the LED array 104 used in the PWM control circuit 101 of FIG. The current IF flowing through the LED of the PWM control circuit 101 of FIG. 10 flows when the voltage V101 becomes higher than the rising voltage V101 'of the LED. Therefore, the current IF flows when the switching element Q101 is oscillating.

  However, the time from when the dimming PWM signal that is a pulse signal rises until the voltage V101 output from the DC / DC converter 103 reaches the voltage V101 ″ through which the set current IF ′ can flow is 0. is not. For this reason, a delay time occurs from the rise of the dimming PWM signal that is a pulse signal until the set current IF ′ flows, so even if a rectangular dimming PWM signal is input, the waveform of the current IF that flows through the LED is It is not rectangular but trapezoidal and has a soft start waveform as shown in FIG.

  That is, when the LED is turned on, the switching element Q101 of the DC / DC converter 103 performs a switching operation after the dimming PWM signal, which is a pulse signal, rises, and the smoothing capacitor is boosted by the function of the choke coil L101. A delay occurs due to the time for accumulating charges in C101.

  On the other hand, when turning off the LED, after the switching operation of the switching element Q101 is stopped, the charge charged in the smoothing capacitor C101, which is an electrolytic capacitor, is discharged throughout the LED (fall time). The current IF continues to flow through the LED.

  For this reason, even if the dimming PWM signal is a rectangular wave, the waveform of the current IF flowing through the LED has a trapezoidal shape. Therefore, the amount of current flowing through the LED becomes a characteristic (characteristic without linearity) that is not exactly proportional to the duty ratio of the dimming PWM signal. Accordingly, the brightness of the LED that is proportional to the amount of current flowing through the LED is also not proportional to the duty ratio of the dimming PWM signal.

  In order to perform dimming over a wide range, the problem is how far the duty ratio of the dimming PWM signal can be reduced (that is, how long the ON time of the dimming PWM signal can be shortened). When the duty ratio is decreased, the voltage V1 increases after the dimming PWM signal rises, and the dimming PWM signal pulse is turned off before the current IF reaches the set current IF '.

  The peak of the current IF during the lighting period varies as the VF-IF characteristic of the LED changes, but the VF-IF characteristic of the LED is sensitive to temperature and the brightness of the LED depends on the amount of current flowing through the LED. Therefore, if the dimming PWM signal is turned off before the current peak value IF reaches the set current peak value IF ′, a predetermined brightness cannot be obtained.

  Here, the reason why the LED flickers as the duty ratio is reduced will be described in more detail with reference to FIGS.

  In FIG. 11A, the lighting period (that is, the period in which the dimming PWM signal that is a pulse signal is ON) can be further divided into a transient period T103 and a steady period T104. In FIG. 11A, the extinguishing period is T102.

  In the transition period T103, the voltage V101 does not reach the voltage V101 ″ that allows the set current peak value IF ′ (hereinafter referred to as “set current IF ′”) to flow. It is a state. In the transition period T103, constant current control is not performed on the current peak value IF (hereinafter referred to as “current IF”) flowing through the LED, and the LED current value is determined by the voltage V101 and the VF-IF characteristics of the LED. ing. Therefore, the transition period T103 is a period in which the current value of the LED changes according to the temperature characteristic of the VF-IF characteristic of the LED.

  During the steady period T104, the voltage V101 reaches the voltage V101 ″ through which the set current IF ′ can flow, and the voltage V101 is feedback-controlled so as to keep the current flowing through the LED constant (set current IF ′). It is in a state.

  FIG. 12 is a graph showing the VF-IF characteristics of the LED. FIG. 12B is a graph showing the VF-IF characteristics of the LED in a state where constant current control is not performed. FIG. 12B shows a state in the transition period T103, and shows a state in which the current IF corresponding to the voltage V101 changes (varies) with temperature. In the state shown in FIG. 12B, flicker is visually recognized in the LED due to a change in the current IF flowing through the LED.

  FIG. 12A is a graph showing the VF-IF characteristics of the LED in a state where constant current control is performed. FIG. 12A shows a state in the steady period T104, in which the voltage V101 is varied (feedback controlled) and the current IF corresponding to the voltage V101 is kept constant. Since the voltage V101 is varied to make the current IF corresponding to the voltage V101 constant, the LED VF-IF characteristics are not affected by changes according to temperature.

  In the transition period T103, the current IF flowing through the LED changes (fluctuates) as the VF-IF characteristic of the LED changes according to the temperature. On the other hand, in the steady period T104, constant current control is performed so that the current IF flowing through the LED becomes constant.

  Therefore, when the steady period T104 is longer than the transition period T103, even if the current IF flowing through the LED changes during the transition period T103, the change in the current IF during the lighting period T101 is small, and flicker or the like occurs in the LED. Hateful.

  On the other hand, FIG. 13 is an explanatory diagram of a state where the duty ratio of the dimming PWM signal is reduced in the PWM control circuit, and the dimming is performed only in the transition period without the steady period. As shown in the waveform diagram of FIG. 13 (a), in the PWM control circuit 101 of FIG. 10, the duty ratio of the dimming PWM signal is reduced, the steady period is eliminated, and the dimming is performed only in the transient period T103 ′. Since the change in the current IF in the lighting period T101 ′ becomes large, flickering tends to occur in the LED. Since constant current control is not performed in the lighting period T101 ', the current IF in the lighting period T101' does not reach the set current IF '.

  In FIG. 13A, the extinguishing period is T102 '. FIG. 13B shows the LED VF used in a state where the duty ratio of the dimming PWM signal is reduced in the PWM control circuit 101 of FIG. 10 and the steady period is eliminated and dimming is performed only in the transient period T103 ′. It is a graph which shows -IF characteristic.

  From the above, since the lower limit of the minimum duty ratio of the dimming PWM signal is limited by the restriction of the delay time until the current flowing through the LED reaches the set value (target value for constant current control), a wide range of adjustments are required. It was difficult to realize light. In particular, since the VF-IF characteristics of an LED easily change according to temperature, the brightness of the LED changes depending on the temperature, or the length of the transient period changes even with the same set current. Changes to cause flickering.

  In addition, in the invention according to Patent Document 1, in the case of constant voltage control, the brightness is changed by changing the current peak value flowing through the LED, but the color (light emission wavelength) of the LED changes depending on the current peak value flowing through the LED. This is not preferable. There is no problem if it is used for mere incoming call display, but it is not preferred for use in a lighting device or a liquid crystal backlight in which color is a problem.

  Furthermore, in the invention according to Patent Document 2, since the LED drive voltage becomes 0 when the LED is turned off, the transition time for raising the LED drive voltage to a predetermined value when the LED is turned on becomes longer and the dimming range becomes narrower.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a light-emitting diode drive dimming circuit, a light-emitting diode illuminating device, a light-emitting diode backlight device, and a liquid crystal capable of a wide range of dimming. It is to provide a display device.

  In order to solve the above problems, a light-emitting diode drive dimming circuit according to the present invention is configured by one light-emitting diode or a light-emitting diode array configured by connecting a plurality of light-emitting diodes in series. A light-emitting diode drive dimming circuit that modulates the current flowing to the light source and adjusts the brightness of the light-emitting diode array, and is applied to the light-emitting diode array during a period in which the light-emitting diode array is lit Dividing the applied DC voltage and holding it as a comparison reference voltage, and performing constant voltage control using the applied DC voltage as a constant voltage based on the comparison reference voltage during a period when the LED array is extinguished. Features.

  According to the invention, constant voltage control is performed based on the comparison reference voltage during a period in which the light emitting diode row is turned off. Thereby, when the light emitting diode row is turned on again, the voltage during the period when the light emitting diode row is turned on can be applied to the light emitting diode row.

  Therefore, the delay time until the current flowing through the light emitting diode array reaches the constant current set value can be minimized. For this reason, even when the duty ratio of the pulse signal in the pulse width modulation is reduced, it is possible to operate the light emitting diode driving dimming circuit with the current flowing through the light emitting diode row being at the constant current set value. is there. Therefore, it is possible to provide a light-emitting diode drive dimming circuit, a light-emitting diode backlight device, and a liquid crystal display device that can perform a wide range of dimming (duty ratio minimization), which has been difficult with conventional circuits.

  In the light emitting diode drive dimming circuit, the transient period in which the voltage applied to the light emitting diode array rises, which is generated in the conventional PWM control circuit, can be minimized. Therefore, even if the duty ratio of the pulse signal in the pulse width modulation is reduced, the light emitting diode drive adjustment is performed in a state in which the lighting period is constituted only by a period in which the voltage applied to the light emitting diode row is constant. The optical circuit can be operated. Therefore, the brightness of the light emitting diode array does not change according to the temperature, and flickering does not occur in the light emitting diode array.

  Further, in the light emitting diode drive dimming circuit, the change in the voltage applied to the light emitting diode array is smaller than in the conventional PWM control circuit. For this reason, it is more advantageous than the conventional circuit from the viewpoint of energy saving.

  Further, in the light emitting diode drive dimming circuit, the output voltage in the lighting period provided immediately before the light emitting diode line is turned off (peak sampling) during the light emitting diode line turned off period. Thereby, when the lighting period of the light emitting diode row starts, the current of the constant current set value can be supplied to the light emitting diode row. Therefore, it is possible to minimize the soft start in the waveform of the current flowing through the light-emitting diode array and realize a rectangular wave current waveform whose head is the constant current set value. Therefore, the brightness of the light-emitting diode array is adjusted in a state where the amount of current flowing through the light-emitting diode array is proportional to the duty ratio of the pulse signal in the pulse width modulation (characteristic having linearity). Light).

  In the light emitting diode drive dimming circuit, power supply means for outputting a drive DC voltage for driving the light emitting diode drive dimming circuit, and DC-DC conversion means for converting the drive DC voltage into the applied DC voltage; In accordance with a pulse signal input from the outside, a switching element for turning on the light emitting diode row by passing the current or turning off the light emitting diode row by cutting off the current, and the light emitting diode row, Constant current feedback means for controlling the current flowing in the light emitting diode row to be constant during the lighting period, and for the DC-DC conversion means during the light emitting diode row is extinguished. Constant voltage feedback means for performing the constant voltage control for maintaining the applied DC voltage during a period when the light emitting diode row is lit, and the light emitting diode. An operation switching means for causing the constant current feedback means to perform the control during a period when the power supply string is lit, and for causing the constant voltage feedback means to perform the constant voltage control during a period when the light emitting diode string is turned off. You may have. Thus, constant voltage control can be performed based on the comparison reference voltage during the period when the light emitting diode row is turned off.

In any one of the light-emitting diode drive dimming circuits, the light-emitting diode row includes a plurality of the light-emitting diode rows,
There may be further provided a current dividing means for dividing the current into a plurality of the light emitting diode rows. By providing the current dividing means, the number of parts can be reduced as compared with the case where the constant current control is individually performed for each light emitting diode array.

  Since the light-emitting diode illuminating device of the present invention includes any one of the above-described light-emitting diode drive dimming circuits, dimming can be performed over a wide range without flicker.

  In addition, since the light-emitting diode backlight device of the present invention includes any one of the above-described light-emitting diode drive dimming circuits, dimming can be performed over a wide range without flickering.

  The liquid crystal display device of the present invention includes the light emitting diode backlight device and a liquid crystal panel.

  Therefore, it is possible to express a dark image by reducing the brightness of the light emitting diode backlight device, and thus it is possible to reproduce the image with high contrast.

  As described above, the light-emitting diode drive dimming circuit of the present invention divides the applied DC voltage applied to the light-emitting diode array during the period when the light-emitting diode array is lit, and holds it as a comparison reference voltage. During the period when the light emitting diode row is turned off, constant voltage control is performed with the applied DC voltage as a constant voltage based on the comparison reference voltage.

  Therefore, there is an effect of providing a light-emitting diode drive dimming circuit, a light-emitting diode illuminating device, a light-emitting diode backlight device, and a liquid crystal display device capable of dimming a wide range.

It is a circuit diagram of the LED drive light control circuit which concerns on the Example of this invention. (A) is a wave form diagram which shows each waveform in the LED drive light control circuit of FIG. 1, (b) is a graph which shows the VF-IF characteristic of the LED row | line | column used in the LED drive light control circuit of FIG. It is a circuit diagram of the LED drive light control circuit which concerns on the other Example of this invention. (A) is a wave form diagram which shows each waveform in the LED drive light control circuit of FIG. 3, (b) is a graph which shows the VF-IF characteristic of the LED row | line | column used in the LED drive light control circuit of FIG. FIG. 6 is a circuit diagram of a multi-stone insulated converter according to another embodiment of the present invention. It is a circuit diagram of the non-insulated converter which concerns on the other Example of this invention. It is a circuit diagram of the other LED drive light control circuit which concerns on the Example of this invention. It is a figure which shows the LED backlight apparatus which concerns on embodiment of this invention. It is a figure which shows the liquid crystal TV which concerns on embodiment of this invention. It is a circuit diagram of a conventional PWM control circuit. (A) is a wave form diagram which shows each waveform in the PWM control circuit of FIG. 10, (b) is a graph which shows the VF-IF characteristic of the LED row | line | column used in the PWM control circuit of FIG. It is a graph which shows the VF-IF characteristic of LED row, (a) is a graph which shows the VF-IF characteristic of LED row in the state which is performing constant current control, (b) is not performing constant current control. It is a graph which shows the VF-IF characteristic of the LED row in a state. FIG. 11 is an explanatory diagram of a state in which the duty ratio of the dimming PWM signal is reduced in the PWM control circuit, the steady period is eliminated and the dimming is performed only in the transient period, and (a) is a dimming PWM in the PWM control circuit of FIG. FIG. 11 is a waveform diagram showing a state in which the duty ratio of the signal is reduced and the steady period is eliminated and the light is dimmed only in the transition period, and FIG. And it is a graph which shows the VF-IF characteristic of the LED row | line | column used in the state which dimmed only in the transition period when there was no steady period.

  An embodiment of the present invention will be described below with reference to FIGS. 1, 2, and 7. FIG. First, an embodiment of the present invention will be described with reference to FIGS.

[Example 1]
FIG. 1 is a circuit diagram of an LED drive dimmer circuit 1 (light emitting diode drive dimmer circuit) according to the first embodiment. The LED drive dimming circuit is a circuit that performs PWM modulation (Pulse Width Modulation) to adjust the brightness of the LED array 9 (light control). It is.

  In FIG. 1, an LED drive dimming circuit 1 generally includes a DC power source 2, a DC / DC converter 3, an LED dimming unit 4, a constant voltage feedback circuit 5 (constant voltage feedback means), and a constant current feedback circuit 6. (Constant current feedback means) and a switch control circuit 10 (operation switching means).

  The DC / DC converter 3 includes a switching element Q1, a control IC 7, an IC power supply 8, a choke coil L1, a backflow prevention diode D1, and a smoothing capacitor C1.

  The LED dimming unit 4 includes an LED array 9 and a switching element Q2 (switching element). The LED array 9 is composed of one LED (Light Emitting Diode) or a plurality of LEDs connected in series. Further, the voltage across the LED array 9 is VF. Furthermore, since the LED dimming part 4 has the switching element Q2, the lighting time can be controlled.

  The constant voltage feedback circuit 5 includes an operational amplifier IC1, switches SW1 and SW2 (operation switching means), a capacitor C2, and resistors R1 to R3.

  The constant current feedback circuit 6 includes an operational amplifier IC2, a switch SW3 (operation switching means), a reference power supply 11, and a resistor R4.

  In the LED drive dimming circuit 1 of FIG. 1, the output of the DC power source 2 is connected to one end of the choke coil L1. The other end of the choke coil L1 is connected to the drain of the switching element Q1 and the anode of the backflow prevention diode D1. The output of the control IC 7 is connected to the gate of the switching element Q1. The output of the IC power supply 8 is connected to the power supply input of the control IC 7.

  The cathode of the backflow prevention diode D1 is connected to one end of the smoothing capacitor C1, the input of the LED string 9, and one end of the resistor R1. The output of the LED array 9 is connected to the drain of the switching element Q2. A dimming PWM signal, which is a pulse signal, is input to the gate of the switching element Q2. The source of the switching element Q2 is connected to one end of the resistor R4 and the first input of the operational amplifier IC2. The output of the reference power supply 11 is connected to the second input of the operational amplifier IC2. The output of the operational amplifier IC2 is connected to one end of the switch SW3.

  The other end of the resistor R1 is connected to the first input of the operational amplifier IC1, one end of the resistor R2, and one end of the switch SW2. The other end (point A) of the switch SW2 is connected to the second input of the operational amplifier IC1, one end of the resistor R3, and one end of the capacitor C2. The output of the operational amplifier IC1 is connected to one end of the switch SW1.

  The other end of the switch SW1 and the other end of the switch SW3 are connected to the first control input of the control IC 7.

  The first to third outputs of the switch control circuit 10 are connected to the control inputs of the switches SW1 to SW3, respectively.

  The input of the DC power source 2, the GND input of the control IC 7, the source of the switching element Q1, the other end of the smoothing capacitor C1, and the other end of the resistor R4 are connected to each other. The other ends of the resistors R2 and R3 and the other end of the capacitor C2 are electrically grounded.

  In the LED drive dimming circuit 1 of FIG. 1, a DC power supply 2 (power supply means) supplies an input voltage Vin (drive DC voltage) to the DC / DC converter 3. A voltage obtained by rectifying an AC voltage output from an AC power supply different from the DC power supply 2 may be supplied to the DC / DC converter 3 as the input voltage Vin. The IC power supply 8 outputs a voltage of 5 V, for example, to the control IC 7.

  The control IC 7 included in the DC / DC converter 3 controls ON / OFF of the switching element Q1. As a result, the switching frequency of the switching element Q1 or the pulse width (switching pulse width) of the switching pulse output from the switching element Q1 is changed, and the output voltage V1 of the DC / DC converter 3 (DC-DC converting means) ( The applied DC voltage is changed.

  The constant current feedback circuit 6 obtains a rectangular wave voltage Va from the input voltage Vin by controlling the duty of the switching element Q1 during the ON period of the dimming PWM signal (rectangular wave). The rectangular wave voltage Va is smoothed by the smoothing capacitor C1 to obtain the voltage V1 (the output voltage of the DC / DC converter 103).

  In the LED drive dimming circuit 1 of FIG. 1, in the dimming operation using PWM control, the lighting period T1 (lighting period) of the LED array 9 and the unlighting period T2 (non-lighting period) of the LED array 9 Is switched by the switching element Q2 to which the dimming PWM signal is input. Here, the switching frequency of the switching element Q1 included in the DC / DC converter 3 is within a range of several tens of kHz to 100 kHz (within the same range as a normal DC / DC converter). On the other hand, the frequency of the dimming PWM signal is in the range of 100 Hz to 500 Hz. Therefore, the switching element Q2 is an element that performs slow switching unlike the switching element Q1. In the control by the switching element Q2, a current IF is supplied to the LEDs of the LED array 9 during the lighting period T1 of the LED array 9. On the other hand, the current IF is not supplied to the LEDs of the LED array 9 during the turn-off period T2 of the LED array 9. In the following description, the lighting period T1 of the LED string 9 and the extinguishing period T2 of the LED string 9 will be described.

(Operation of LED row 9 during lighting period T1)
In the lighting period T1 of the LED string 9, the switch SW1 of the constant voltage feedback circuit 5 is opened, the switch SW3 of the constant current feedback circuit 6 is closed, and the constant current feedback circuit 6 supplies a constant current to the DC / DC converter 3. Take control. That is, the operation is performed so that the current IF flowing through the LED array 9 is constant (set current IF ′, see FIG. 2A).

  In the constant current control, the operational amplifier IC2 compares the voltage across the resistor R4 that the constant current feedback circuit 6 has and the same current IF as the LED string 9 flows, and the reference voltage Vref. In accordance with the comparison result, the voltage V1 applied to the LED array 9 is increased or decreased to operate the current IF flowing in the LED array 9 to be constant.

  In the lighting period T1 of the LED row 9, the constant voltage feedback circuit 5 keeps the switch SW2 closed. As a result, the voltage at point A is held as a comparison reference voltage. The comparison reference voltage is a voltage obtained by dividing the output voltage V1 when the LED array 9 is lit by the resistors R1 and R2. By charging the capacitor C2 with the voltage obtained by dividing the output voltage V1 by the resistors R1 and R2, the voltage across the capacitor C2 of the constant voltage feedback circuit 5 becomes the voltage obtained by dividing the output voltage V1 by the resistors R1 and R2. Become.

(Operation of LED row 9 during turn-off period T2)
Next, in the turn-off period T2 of the LED string 9, in the constant voltage feedback circuit 5, the switch SW1 is closed and the switch SW2 is opened. In the constant current feedback circuit 6, the switch SW3 is also opened.

  Here, the voltage at the point A is held at a voltage obtained by dividing the output voltage V1 at the timing when the LED string 9 is extinguished (immediately before the LED string 9 is extinguished) by the resistors R1 and R2. The resistance value r3 of the resistor R3 is set to a very large value compared to the resistance value r1 of the resistor R1 and the resistance value r2 of the resistor R2 (r3 >> r1, r3 >> r2). This is because the electric charge accumulated in the smoothing capacitor C1 is used to maintain the voltage at the point A while the dimming PWM signal is OFF. The electric charge accumulated in the smoothing capacitor C1 is 1 in the dimming PWM signal. The resistor R3 having a resistance value r3 that is high enough not to discharge through the resistor R3 during the time when one pulse is ON is used.

  In the turn-off period T2 of the LED string 9, the constant voltage feedback circuit 5 performs constant voltage control so that the output voltage V1 is maintained at the output voltage of the turn-on period T1 of the LED string 9. Specifically, the switch SW3 of the constant current feedback circuit 6 is opened during the extinguishing period T2 of the LED string 9, and the constant voltage feedback circuit 5 performs constant voltage control on the DC / DC converter 3.

  In the constant voltage control, the operational amplifier IC1 compares the voltage of the constant voltage feedback circuit 5 divided by the resistor R1 and the resistor R2 to which the voltage V1 is applied, and the voltage of the smoothing capacitor C1. In accordance with the comparison result, the voltage V1 is increased or decreased by controlling the switching duty ratio so that the voltage V1 becomes constant.

  As described above, in the LED drive dimming circuit 1 of FIG. 1, the output voltage V1 at the timing when the LED array 9 is turned off (the output voltage when the LED array 9 is lit) is used as the reference voltage for peak sampling ( The constant voltage feedback circuit 5 performs constant voltage control based on the comparison reference voltage during the extinguishing period T2 of the LED string 9.

  As a result, at the next timing when the LED row 9 is turned on, the LED drive dimming circuit 1 can be started in a state where the output voltage V1 is the output voltage when the LED row 9 is turned on. The delay time until the current IF flowing through the column 9 reaches a constant current set value (set current IF ′, see FIG. 2) can be minimized. For this reason, even when the duty ratio of the dimming PWM signal (duty ratio of the pulse signal in the pulse width modulation) is reduced, the LED driving dimming circuit 1 operates with the current flowing through the LED array 9 being the set current IF ′. Thus, a wide range of dimming (duty ratio minimization), which was difficult with the conventional circuit, is possible.

  The use of the LED drive dimming circuit 1 shown in FIG. 1 will be described below with reference to FIG. FIG. 2A is a waveform diagram showing each waveform in the LED drive dimming circuit 1 of FIG. FIG. 2B is a graph showing the VF-IF characteristics of the LED array 9 used in the LED drive dimming circuit 1 of FIG.

  Problems in the circuit using the prior art are as follows. That is, in the circuit using the conventional technique, when the duty ratio of the dimming PWM signal is decreased, the current flowing through the LED array does not reach the constant current set value (set current IF ′) during the lighting period of the LED array. . For this reason, the peak of the current flowing through the LED array during the lighting period of the LED array is affected by the change in the VF-IF characteristics of the LED array depending on the temperature. Therefore, the brightness of the LED array changes according to the temperature, or flickering occurs in the LED array.

  In the LED drive dimming circuit 1 of FIG. 1, during the extinguishing period T2 of the LED string 9, the output voltage in the lighting period T1 provided immediately before the extinguishing period T2 of the LED string 9 is peak-sampled. Thereby, when the lighting period T1 of the LED string 9 starts, the LED drive dimming circuit 1 is operated in a state where the output voltage V1 is an output voltage necessary for flowing the set current IF ′ to the LED string 9. I can do it.

  For this reason, the LED drive dimming circuit 1 of FIG. 1 minimizes the transient period T103 (transient period in which the output voltage V1 rises) in FIG. 11A, which occurred in the conventional PWM control circuit 101 of FIG. I can do it. Therefore, even if the duty ratio of the dimming PWM signal is reduced, the LED drive dimming circuit 1 can be operated in a state in which the lighting period T1 is constituted only by the steady period (period in which the output voltage V1 is constant). I can do it. Therefore, the brightness of the LED array 9 does not change according to the temperature, and the LED array 9 does not flicker.

  Further, in the LED drive dimming circuit 1 in FIG. 1, the change in the output voltage V1 is smaller than that in the PWM control circuit 101 in FIG. For this reason, it is more advantageous than the conventional circuit from the viewpoint of energy saving.

  Further, in the LED drive dimming circuit 1 of FIG. 1, during the extinguishing period T2 of the LED row 9, the output voltage in the lighting period T1 provided immediately before the extinguishing period T2 of the LED row 9 is peak-sampled. Thereby, when the lighting period T1 of the LED string 9 starts, the set current IF 'can be supplied to the LED string 9. Accordingly, it is possible to minimize the soft start in the waveform of the current IF flowing through the LED array 9 and realize a rectangular wave current waveform whose head is the set current IF ′. Therefore, the brightness of the LED array 9 can be adjusted (dimmed) in a state where the amount of current flowing through the LED array 9 is proportional to the duty ratio of the dimming PWM signal (characteristic having linearity). It becomes possible.

  In the LED drive dimming circuit 1 of FIG. 1, the LED dimming unit 4 has one LED row 9, but the case where the LED dimming unit 4 has a plurality of LED rows 9 can also be realized in the same manner. FIG. 7 is a circuit diagram of another LED drive dimming circuit 31 (light emitting diode drive dimming circuit) according to the first embodiment.

  The LED drive dimming circuit 31 of FIG. 7 includes a current balance circuit 33 (a current dividing unit). As the current balance circuit 33, for example, the shunt circuit disclosed in Patent Document 4 can be used.

  In the LED drive dimming circuit 31 of FIG. 7, the LED dimming unit 32 has two LED rows 9. The current balance circuit 33 equally divides the current IF output from the DC / DC converter 3, and causes the LED currents of IF / 2 to flow through the two LED strings 9. Thereby, as FIG. 11 of patent document 4 and FIG. 2 of patent document 3 show, the number of parts can be reduced rather than the case where constant current control is individually performed about each LED row | line | column.

  In the above description, the current balance circuit 33 equally divides the current IF because the two LED rows 9 of the LED dimming unit 32 have the same configuration (for example, the same number of the same LEDs are used). Because). However, the present invention is not limited to this, and the current balance circuit 33 may pass different currents to the plurality of LED strings when, for example, the VF-IF characteristics of the plurality of LED strings are different. The brightness in each LED row can be varied by appropriately changing the current passed through the plurality of LED rows in accordance with the current passed through each LED row and the voltage applied to each LED row.

  In the LED drive dimming circuit 1, a DC power source 2 that outputs an input voltage Vin for driving the LED drive dimming circuit 1, a DC / DC converter 3 that converts the input voltage Vin into an output voltage V1, and an external source In accordance with the input dimming PWM signal, the LED array 9 is turned on by supplying the current IF, or the switching element Q2 that turns off the LED array 9 by cutting off the current IF and the LED array 9 is turned on. A constant current feedback circuit 6 that performs constant current control to increase / decrease the output voltage V1 with respect to the DC / DC converter 3 so that the current IF flowing through the LED string 9 is constant during the lighting period T1, and the LED string 9 A constant voltage feedback circuit 5 that performs the above-described constant voltage control for maintaining the output voltage V1 of the lighting period T1 during which the LED string 9 is lit, with respect to the DC / DC converter 3 during The constant current feedback circuit 6 performs the constant current control during the lighting period T1 when the ED row 9 is lit, and the constant voltage feedback circuit 5 performs the constant voltage control during the extinguishing period T2 when the LED row 9 is off. The switch control circuit 10 and the switches SW1 to SW3 may be provided. Accordingly, constant voltage control can be performed based on the comparison reference voltage during the extinguishing period T2 when the LED row 9 is extinguished.

The LED drive dimming circuit 31 includes a plurality of LED rows 9,
You may further provide the current balance circuit 33 which divides and flows the electric current IF into the some LED row | line | column 9. FIG. By providing the current balance circuit 33, the number of parts can be reduced as compared with the case where the constant current control is individually performed for each LED array 9.

[Example 2]
The following will describe another embodiment of the present invention with reference to FIGS. The configuration other than that described in the second embodiment is the same as that of the first embodiment. For convenience of explanation, members having the same functions as those shown in the drawings of the first embodiment are given the same reference numerals, and explanation thereof is omitted.

  FIG. 3 is a circuit diagram of the LED drive dimming circuit 12 (light emitting diode drive dimming circuit) according to the second embodiment. In FIG. 3, the LED drive dimming circuit 12 generally includes an AC power supply 13 (power supply means), a diode bridge 14 (power supply means), an insulating boost converter 15 (DC-DC conversion means), and an LED dimming unit. 16, a constant voltage feedback circuit 17 (constant voltage feedback means), a constant current feedback circuit 18 (constant current feedback means), and an insulating photocoupler 19. The diode bridge 14 full-wave rectifies the alternating current output from the AC power supply 13. The LED drive dimming circuit 12 includes a transistor power source 20, a transistor Q5, and resistors R4 and R17.

  The insulation type boost converter 15 includes a switching element Q1, a control IC 7, an IC power supply 8, an insulation transformer T, a backflow prevention diode D1, a smoothing capacitor C1, and a resistor R5. The insulating transformer T has a primary winding N1 and a secondary winding N2.

  The LED dimming unit 16 includes an LED array 9 and a switching element Q2. The LED array 9 is composed of one LED (Light Emitting Diode) or a plurality of LEDs connected in series.

  The constant voltage feedback circuit 17 includes operational amplifiers OP2 and OP3, transistors Q4 and Q6 to Q8, capacitors C3 and C4, and resistors R6 to R16.

  The constant current feedback circuit 18 includes an operational amplifier OP1, a transistor Q3, a capacitor C5, and resistors R18 and R19.

  In the LED drive dimming circuit 12 of FIG. 3, one output of the AC power supply 13 is connected to one input of the diode bridge 14. The other output of the AC power supply 13 is connected to the other input of the diode bridge 14. One output of the diode bridge 14 is connected to one end of the primary winding N1 of the isolation transformer T.

  The other end of the primary winding N1 of the insulating transformer T is connected to the drain of the switching element Q1. The output of the control IC 7 is connected to the gate of the switching element Q1. The output of the IC power supply 8 is connected to the power supply input of the control IC 7.

  The source of the switching element Q1 is connected to one end of the resistor R5 and the second control input of the control IC 7. The other end of the resistor R5 is connected to the other output of the diode bridge 14.

  One end of the secondary winding N2 of the insulation transformer T is connected to the anode of the backflow prevention diode D1. The cathode of the backflow prevention diode D1 is connected to one end of the smoothing capacitor C1, the input of the LED string 9, and one end of the resistor R6. The output of the LED array 9 is connected to the drain of the switching element Q2. A dimming PWM signal, which is a pulse signal, is input to the gate of the switching element Q2. The source of the switching element Q2 is connected to one end of the resistor R4 and one end of the resistor R19.

  The other end of the resistor R6 is connected to one end of the resistor R7 and the non-inverting input terminal (+) of the operational amplifier OP3. The inverting input terminal (−) of the operational amplifier OP3 is connected to the output of the operational amplifier OP3, one end of the resistor R8, one end of the resistor R10, and the drain of the transistor Q8. The other end of the resistor R8 is connected to one end of the resistor R9, the non-inverting input terminal (+) of the operational amplifier OP2, the collector of the transistor Q6, one end of the resistor R16, and one end of the capacitor C4.

  The other end of the resistor R10 is connected to the gate of the transistor Q8 and the collector of the transistor Q7. The source of the transistor Q8 is connected to one end of the capacitor C3, one end of the resistor R13, and the inverting input terminal (−) of the operational amplifier OP2.

  A dimming PWM signal is input to one end of the resistor R11 and one end of the resistor R14. The other end of the resistor R11 is connected to one end of the resistor R12 and the base of the transistor Q7. The other end of the resistor R14 is connected to one end of the resistor R15 and the base of the transistor Q6.

  The output of the operational amplifier OP2 is connected to the base of the transistor Q4. The output of the transistor power supply 20 is connected to the collector of the transistor Q4 and the collector of the transistor Q3. The emitter of the transistor Q4 is connected to the emitter of the transistor Q3, one end of the resistor R17, and the base of the transistor Q5.

  The other end of the resistor R16 and the other end of the capacitor C4 are connected to the collector of the transistor Q5, one end of the resistor R18, one end of the capacitor C5, and the input of the insulating photocoupler 19. The output of the insulating photocoupler 19 is connected to the first control input of the control IC 7.

  The other end of the resistor R18 and the other end of the capacitor C5 are connected to the non-inverting input terminal (+) of the operational amplifier OP1 and the other end of the resistor R19.

  A dimming DIM signal to be described later is input to the inverting input terminal (−) of the operational amplifier OP1. The output of the operational amplifier OP1 is connected to the base of the transistor Q3.

  The other end of the resistor R7, the other end of the resistor R9, the emitter of the transistor Q7, the other end of the resistor R12, the other end of the resistor R13, the other end of the capacitor C3, the emitter of the transistor Q6, and the resistor The other end of R15, the other end of resistor R17, the emitter of transistor Q5, the other end of resistor R4, the other end of smoothing capacitor C1, and the other end of secondary winding N2 of insulating transformer T are mutually connected. It is connected.

  In the LED drive dimming circuit 12, the IC power supply 8 outputs a voltage of 5 V, for example, to the control IC 7. The transistor power supply 20 outputs a voltage of, for example, 13 V to the collector of the transistor Q4 and the collector of the transistor Q3.

  The feedback circuit of the isolated boost converter 15 in the LED drive dimming circuit 12 includes a constant current feedback circuit 18 that operates during the lighting period T1 of the LED string 9 and a constant voltage feedback circuit that operates during the extinguishing period T2 of the LED string 9. 17, the constant current control by the constant current feedback circuit 18 is performed during the lighting period, and the OR circuit Q 5 for performing the constant voltage control by the constant voltage feedback circuit 17 and the current IF flowing through the LED array 9 is turned on during the extinction period. The switching element Q2 to be turned off / off and the insulating photocoupler 19 are included.

  Regarding the above feedback circuit, the constant current feedback circuit 18 includes an operational amplifier OP1 (corresponding to the operational amplifier IC2 in FIG. 1) and a peripheral circuit, and the constant voltage feedback circuit 17 is an operational amplifier OP2 (corresponding to the operational amplifier IC1 in FIG. 1). And peripheral circuits.

  The operation of the LED drive dimming circuit 12 will be described below. Based on the dimming PWM signal input to the gate, the switching element Q2 turns on the current IF that flows through the LED array 9 during the lighting period T1 of the LED array 9, and the current that flows through the LED array 9 during the extinguishing period T2 of the LED array 9 A dimming operation for adjusting the brightness of the LED array 9 is performed by turning off the IF.

  The dimming DIM signal is input to the inverting input terminal (−) of the operational amplifier OP1 of the constant current feedback circuit 18 to vary the DC voltage level of the dimming DIM signal. High value can be set. The feedback circuit of the isolated boost converter 15 in the LED drive dimming circuit 12 of FIG. 3 is merely an example, and can be applied regardless of the type of converter.

  The voltage V1 applied to the LED array 9 is divided by resistors R6 and R7, and is output as a voltage buffer by an operational amplifier OP3. In the lighting period T1 of the LED string 9, the transistor Q7 is turned on by the dimming PWM signal which is Hi, and the transistor Q8 is turned on because the gate of the transistor Q8 is LOW. As a result, the output voltage of the operational amplifier OP3 is applied to the inverting input terminal (−) of the operational amplifier OP2.

  The transistors Q4 and Q6 in FIG. 3 perform the function of the switch SW1 in FIG. Similarly, the transistors Q7 and Q8 in FIG. 3 function as the switch SW2 in FIG. 1, and the transistor Q3 in FIG. 3 functions as the switch SW3 in FIG.

  In the lighting period T1 of the LED row 9, the transistor Q6 is also turned on by the dimming PWM signal, and the potential of the non-inverting input terminal (+) of the operational amplifier OP2 is maintained at the GND level.

  For this reason, during the lighting period of the LED string 9, the output of the operational amplifier OP2 is maintained at the LOW level, and the base potential of the transistor Q4 becomes LOW, so that the transistor Q4 does not operate (turns OFF). Therefore, the constant voltage feedback circuit 17 does not participate in the feedback control of the isolated boost converter 15.

  During the turn-off period T2 of the LED row 9, the transistor Q7 is turned off and the transistor Q8 is turned off by the dimming PWM signal. Therefore, the output voltage of the operational amplifier OP3 held by C4 and immediately before the transistor Q8 is turned off is applied to the inverting input terminal (−) of the operational amplifier OP2.

  During the turn-off period T2 of the LED string 9, the transistor Q6 is also turned off, and a voltage obtained by dividing the output voltage of the operational amplifier OP3 by the resistors R8 and R9 is applied to the non-inverting input terminal (+) of the operational amplifier OP2.

  As a result, constant voltage control is performed by the operational amplifier OP2 and the transistors Q4 and Q5. The voltage at the inverting input terminal (−) of the operational amplifier OP2, which is a reference voltage for constant voltage control, is the output voltage of the operational amplifier OP3 held by C4 and immediately before the transistor Q8 is turned off. Thereby, constant voltage control can be performed so that the output voltage of the LED string 9 during the turn-off period T2 becomes the output voltage of the LED string 9 during the lighting period T1.

  FIG. 4A shows the waveform of the lighting period T1 and the waveform of the extinguishing period T2 in the dimming operation described above. FIG. 4A is a waveform diagram showing each waveform in the LED drive dimming circuit 12 of FIG. FIG. 4B is a graph showing the VF-IF characteristics of the LED array 9 used in the LED drive dimming circuit 12 of FIG.

  In the LED drive dimming circuit 12 according to the second embodiment, by performing the feedback control described above, the output during the lighting period T1 provided immediately before the extinguishing period T2 of the LED array 9 during the extinguishing period T2 of the LED array 9 is performed. The voltage is peak sampled. Thereby, the output voltage V1 when the lighting period T1 of the LED array 9 starts can be set to a voltage necessary for flowing the set current IF '. Accordingly, it is possible to minimize the soft start in the waveform of the current IF flowing through the LED array 9 and realize a rectangular wave current waveform whose head is the set current IF ′. Therefore, the brightness of the LED array 9 can be adjusted (dimmed) in a state where the amount of current flowing through the LED array 9 is proportional to the duty ratio of the dimming PWM signal (characteristic having linearity). It becomes possible.

  The resistor R6 in FIG. 3 corresponds to the resistor R1 that divides the output voltage V1 in FIG. Similarly, the resistor R7 in FIG. 3 corresponds to the resistor R2 that divides the output voltage V1 in FIG.

  In FIG. 3, a voltage obtained by dividing the output voltage of the operational amplifier OP3 by the resistor R8 and the resistor R9 is input to the non-inverting input terminal (+) of the operational amplifier OP2. The resistance value r9 of the resistor R9 is The resistance value is considerably larger than the resistance value r8 of the resistor R8 (r9 >> r8), and a voltage substantially equal to the output voltage of the operational amplifier OP3 is input to the non-inverting input terminal (+) of the operational amplifier OP2.

  Further, the capacitor C3 in FIG. 3 corresponds to the capacitor C2 in FIG. 1, and the resistor R13 in FIG. 3 corresponds to the resistor R3 in FIG.

  In the LED drive dimming circuit 12 according to the second embodiment, the isolated boost converter 15 that is a one-stone insulated converter is used. However, instead of the insulated boost converter 15, the multi-stone insulated circuit shown in FIG. A type converter 41 (DC-DC converting means) may be used, or a non-insulated converter 42 (DC-DC converting means) shown in FIG. 6 may be used. The multi-stone insulated converter 41 has a switching element Q9 and a capacitor C6. In addition, the LED drive dimming circuit 12 according to the second embodiment includes one LED row 9, but the LED drive dimming circuit 12 is also applied to the plurality of LED rows 9 illustrated in FIG. I can do it.

  A feature of the present invention is that in a circuit that performs dimming by PWM-controlling the current IF flowing through the LED array 9, the voltage V1 applied to the LED array 9 is controlled at a constant voltage during non-dimming (when the LED array 9 is turned off). The power supply circuit is not limited to the DC / DC converter, and is not limited to the number of LEDs or LED strings connected in series.

[Use of LED drive dimming circuit]
The LED drive dimming circuit according to the present embodiment includes, for example, a power source of a liquid crystal TV (liquid crystal display device) 61 as shown in FIG. 9 and an LED backlight device 51 (light emitting diode) for a liquid crystal display device as shown in FIG. It can be used for a power source of a backlight device) or an LED lighting device (light emitting diode lighting device), and an image without flicker can be obtained even on a dark screen where the brightness of the LED backlight device 51 is lowered.

  The LED backlight device 51 shown in FIG. 8 includes an LED 52, an optical sheet 53 that makes the brightness uniform, and a frame 54, and a liquid crystal panel 62 is attached to the surface, whereby the liquid crystal shown in FIG. It becomes TV61.

  Since the LED lighting device according to the present embodiment includes any one of the LED drive dimming circuits 1, 12, and 31, dimming can be performed over a wide range without flickering.

  Moreover, since the LED backlight device 51 according to the present embodiment includes any one of the LED drive dimming circuits 1, 12, and 31, dimming can be performed over a wide range without flickering.

  The liquid crystal TV 61 according to this embodiment includes an LED backlight device 51 and a liquid crystal panel 62.

  Therefore, it is possible to express a dark image by reducing the brightness of the light emitting diode backlight device, and thus it is possible to reproduce the image with high contrast.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  Since the light-emitting diode drive dimming circuit of the present invention can adjust light in a wide range, it can be suitably used for liquid crystal backlights such as liquid crystal TVs, monitors, and information displays, LED lighting devices, and LED application products.

1,12,31 LED drive dimmer circuit (light emitting diode drive dimmer circuit)
2 DC power supply (power supply means)
3 DC / DC converter (DC-DC converter)
4, 16, 32 LED dimming unit 5, 17 Constant voltage feedback circuit (constant voltage feedback means)
6,18 Constant current feedback circuit (constant current feedback means)
7 Control IC
8 IC power supply 9 LED row (light emitting diode row)
10 Switch control circuit (operation switching means)
11 Reference power supply 13 AC power supply (power supply means)
14 Diode bridge (power supply means)
15 Insulation type boost converter (DC-DC conversion means)
19 Insulating Photocoupler 20 Transistor Power Supply 33 Current Balance Circuit (Diversion Means)
41 Multi-stone type isolated converter (DC-DC conversion means)
42 Non-insulated converter (DC-DC conversion means)
51 LED backlight device (light emitting diode backlight device)
52 LED
53 Optical sheet 61 Liquid crystal TV (Liquid crystal display device)
62 Liquid crystal panel C1 Smoothing capacitor C2 to C6 Capacitor D1 Backflow prevention diode IC1, IC2, OP1 to OP3 Operational amplifier IF current IF 'Setting current L1 Choke coil N1 Primary winding N2 Secondary winding Q1, Q9 Switching element Q2 Switching element ( Switching element)
Q3 to Q8 Transistors R1 to R19 Resistors SW1 to SW3 Switches (operation switching means)
T Isolation transformer T1 Lighting period (lit period)
T2 extinguishing period (extinguishing period)
V1 output voltage (applied DC voltage)
Va square wave voltage Vin input voltage (drive DC voltage)
Vref reference voltage r1 to r3, r8, r9 resistance value

Claims (6)

The brightness of the light emitting diode row is adjusted by pulse-width-modulating a current flowing through the light emitting diode row constituted by one light emitting diode or a plurality of light emitting diodes connected in series. A light-emitting diode drive dimming circuit comprising:
During the period when the light emitting diode row is lit, the applied DC voltage applied to the light emitting diode row is divided and held as a comparison reference voltage,
A light-emitting diode drive dimming circuit that performs constant voltage control using the applied DC voltage as a constant voltage based on the comparison reference voltage during a period when the light-emitting diode array is turned off. Power supply means for outputting a driving DC voltage for driving the light emitting diode driving dimming circuit;
DC-DC converting means for converting the driving DC voltage into the applied DC voltage;
In accordance with a pulse signal input from the outside, the current is turned on to turn on the light emitting diode row, or the switching element that cuts off the current and turns off the light emitting diode row,
Constant current feedback means for performing control so that the current flowing through the light emitting diode array is constant during the period in which the light emitting diode array is lit;
Constant voltage feedback means for performing the constant voltage control for maintaining the applied DC voltage during the period when the light emitting diode row is lit with respect to the DC-DC conversion means during the period when the light emitting diode row is turned off. When,
Operation switching means for causing the constant current feedback means to perform the control during a period in which the light emitting diode string is lit, and for causing the constant voltage feedback means to perform the constant voltage control in a period during which the light emitting diode string is not lit. The light-emitting diode drive dimming circuit according to claim 1. A plurality of the light emitting diode rows are provided,
The light-emitting diode drive dimming circuit according to claim 1, further comprising a shunting unit that divides the current into a plurality of the light-emitting diode rows.   A light-emitting diode illuminating device comprising the light-emitting diode drive dimming circuit according to claim 1.   A light-emitting diode backlight device comprising the light-emitting diode driving dimming circuit according to claim 1.   A liquid crystal display device comprising the light-emitting diode backlight device according to claim 5 and a liquid crystal panel.