JP2015135738A - Light source drive device and illuminating fixture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light source drive device capable of making a relation between a level of a dimming instruction signal and a level of an output current be linear over a wider dimming region.SOLUTION: A light source drive device 1 outputs a dimming signal Sc from a dimming control part 5 to a drive circuit part 2 on the basis of a dimming instruction signal Sad that is a PWM signal to supply a current based on the dimming signal Sc from the drive circuit part 2 to an LED module 12. The dimming control part 5, in a case where an on-duty of the dimming instruction signal Sad is a predetermined value or more, outputs a DC voltage dimming signal corresponding to a first DC voltage signal generated on the basis of the dimming instruction signal Sad as the dimming signal Sc. The dimming control part 5, in a case where the on-duty of the dimming instruction signal Sad is less than the predetermined value, generates a PWM dimming signal using a value corresponding to a second DC voltage signal, that is a predetermined value, as a peak value on the basis of the dimming instruction signal Sad, and outputs the PWM dimming signal as the dimming signal Sc to the drive circuit part 2.

Description

  The present invention relates to a light source driving device and a lighting fixture, and more particularly to a light source driving device and a lighting fixture capable of dimming control of a light source.

  For example, in a lighting fixture using an LED (light emitting diode) module or the like as a light source, a light source driving device performs control based on a dimming instruction signal input by a user so that the light source can be dimmed.

  Patent Document 1 below describes a power supply device that performs such dimming control. In this power supply device, the switching timing of the switching element from on to off is controlled by comparing the reference signal generated from the dimming instruction signal and the detection signal proportional to the current flowing through the switching element, and the current flows through the inductor The switching timing of the switching element from OFF to ON is controlled based on the induced voltage proportional to the current, and the DC-DC converter is configured to operate in a so-called current critical mode.

JP2013-27200A

  By the way, in the power supply device as described in the above-mentioned Patent Document 1, there is a case where a problem occurs when performing deep dimming (dark dimming). Hereinafter, such a problem will be described by taking as an example the case where the dimming instruction signal is a PWM (pulse width modulation) type signal.

  FIG. 7 is a diagram illustrating an example of the output current Io with respect to the on-duty of the dimming instruction signal in the conventional power supply device.

  As shown in FIG. 7, when the current flowing through the inductor is controlled in a so-called continuous mode or critical mode in a relatively shallow light control region (light control region where the light source is bright), the magnitude of the light control instruction signal is large. The relationship between the value (the on-duty value of the dimming instruction signal) and the output current Io is linear. For example, as indicated by line AB, the relationship between the two becomes linear when the dimming instruction signal is in the range of about 100% to 30%.

  On the other hand, when dimming deeper than this, the current flowing through the inductor becomes a so-called discontinuous mode, and the relationship between the two becomes nonlinear. For example, as indicated by the line BC, the dimming instruction signal is non-linear when the magnitude of the dimming instruction signal is less than 30%.

  Thus, in the conventional power supply device, the range of the dimming region where the relationship between the magnitude of the dimming instruction signal and the output current Io is linear is limited. Therefore, when changing the degree of dimming from point A to point C (when illuminance is lowered from shallow dimming to deep dimming), or when changing from point C to point A (deep dimming to shallow dimming) When the illuminance is increased to light), the change in the output current Io with respect to the change in the magnitude of the dimming instruction signal is a linear change or a non-linear change, or is switched at a point B in the middle.

  As described above, a dimming characteristic in which the relationship between the dimming instruction and the degree of dimming differs greatly between shallow dimming and deep dimming is generally preferred as a dimming characteristic of the light source driving device. There is nothing.

  The present invention has been made to solve such a problem, and a light source driving device and illumination capable of linearizing the relationship between the magnitude of the dimming instruction signal and the output current Io over a wider dimming region. The purpose is to provide equipment.

  In order to achieve the above object, according to one aspect of the present invention, a light source driving device that drives a light source by supplying a current to a light source based on a dimming instruction signal that is a PWM signal is adjusted based on the dimming instruction signal. A dimming control unit that outputs an optical signal and a drive circuit unit that supplies a current to the light source based on the dimming signal. The drive circuit unit turns on / off an inductor connected to the light source and a current flowing through the inductor. A converter circuit unit including a switch element that is changed by operation, a current detection resistor that detects a current flowing through the inductor, and a converter that controls on / off operation of the switch element based on a detection result of the current detection resistor and a dimming signal A dimming control unit corresponding to the first DC voltage signal generated based on the dimming instruction signal when the on-duty of the dimming instruction signal is equal to or greater than a predetermined value. When the on-duty of the dimming instruction signal is less than the predetermined value, the PWM dimming is performed with the value corresponding to the second DC voltage signal being the predetermined value as the peak value. The optical signal is generated based on the dimming instruction signal, and the PWM dimming signal is output to the drive circuit unit as the dimming signal.

  Preferably, when the DC voltage dimming signal is input as the dimming signal, the converter control unit outputs the first PWM signal generated based on the DC voltage dimming signal to the switch element to turn on / off the switch element. When a PWM dimming signal is input as a dimming signal by controlling the off operation, the second PWM signal generated based on the PWM dimming signal is output to the switch element, and the switch element intermittently turns on / off. Control to be done automatically.

  Preferably, the converter control unit controls the on / off operation of the switch element so that a current flows through the inductor in a critical mode.

  Preferably, the dimming control unit includes a signal conversion circuit that generates a first DC voltage signal based on the dimming instruction signal, a reference signal generation circuit that generates a reference signal based on the dimming instruction signal, and a first A PWM dimming signal generation circuit that generates a PWM dimming signal based on a comparison result between the DC voltage signal and the reference signal, a DC voltage signal generation circuit that generates a second DC voltage signal based on the reference signal, A DC voltage value limiting circuit that sets a lower limit voltage value of the first DC voltage signal based on the second DC voltage signal.

  According to another aspect of the present invention, a lighting fixture includes a light source, the above-described light source driving device that drives the light source, and a dimming control device that outputs a dimming instruction signal to the light source driving device.

  According to these inventions, when the on-duty of the dimming instruction signal is less than the predetermined value, the dimming control unit generates a PWM dimming signal having the predetermined value as the peak value based on the dimming instruction signal. It is output to the drive circuit unit as an optical signal. Therefore, it is possible to provide a light source driving device and a lighting fixture that can make the relationship between the magnitude of the dimming instruction signal and the magnitude of the output current linear over a wider dimming area.

It is a block diagram which shows the structure of the lighting fixture using the light source drive device in one of embodiment of this invention. It is a figure which shows the structure of a light source drive device. It is a circuit diagram which shows the structure of a light control part. It is a wave form diagram explaining the light control operation | movement in this Embodiment. It is a graph showing the relationship of the output current with respect to the on-duty of a light control instruction | indication signal. It is a circuit diagram which shows the modification of a DC voltage value limiting circuit. It is a figure which shows an example of the magnitude | size of the output current with respect to the on-duty of the light control instruction | indication signal in the conventional power supply device.

  Hereinafter, the lighting fixture using the light source drive device in embodiment of this invention is demonstrated.

  [Embodiment]

  FIG. 1 is a block diagram showing a configuration of a lighting fixture using a light source driving device according to one embodiment of the present invention.

  As illustrated in FIG. 1, the lighting fixture 100 includes a light source driving device 1, an LED module (an example of a light source) 12, and a dimming control device 80. The luminaire 100 performs illumination when the LED module 12 is driven and turned on.

  In the present embodiment, the LED module 12 is an LED unit formed by connecting a plurality of LEDs in series. The LED module 12 may be a single LED. The LED module 12 may have a configuration in which a plurality of LED units are connected in parallel or in series.

  The light source driving device 1 is connected to the LED module 12. The light source driving device 1 drives the LED module 12.

  In the present embodiment, the light source driving device 1 is connected to the dimming control device 80. The dimming control device 80 outputs a dimming instruction signal Sad to the light source driving device 1. The light source driving device 1 performs a dimming operation of the LED module 12 based on the dimming instruction signal Sad sent from the external dimming control device 80. That is, in the lighting fixture 100, the brightness of the illumination by the LED module 12 can be changed.

  The dimming instruction signal Sad is a PWM signal having a duty ratio corresponding to the degree of dimming. As the on-duty of the dimming instruction signal Sad increases, the LED module 12 is dimmed shallower (brighter) and lights up. The smaller the on-duty of the dimming instruction signal Sad, the deeper (darker) dimming of the LED module 12 is lit.

  The dimming control device 80 is, for example, a remote controller provided in the lighting fixture 100 in order to change the brightness. The connection between the light control device 80 and the light source driving device 1 may be wired or wireless. For example, when the dimming control device 80 and the light source driving device 1 are connected wirelessly, a light emitting unit is provided in the dimming control device 80, a light receiving unit is provided in the light source driving device 1, and infrared communication is performed between the two. It may be configured to perform.

  FIG. 2 is a diagram illustrating a configuration of the light source driving device 1.

  As shown in FIG. 2, the light source driving device 1 roughly includes a drive circuit unit 2 and a dimming control unit 5. The light source driving device 1 receives a DC voltage from the DC power supply Vdc, a DC voltage from the DC power supply Vcc, and a dimming instruction signal Sad. The light source driving device 1 supplies the output current Io to the LED module 12 and drives the LED module 12.

  The dimming control unit 5 receives a DC voltage from the DC power supply Vcc and a dimming instruction signal Sad. The dimming control unit 5 generates a dimming signal Sc based on these signals, and outputs the generated dimming signal Sc to the drive circuit unit 2.

  The drive circuit unit 2 includes a converter circuit unit 3, a converter control unit 4, and a current detection resistor R1. The drive circuit unit 2 supplies the output current Io from the converter circuit unit 3 to the LED module 12 based on the dimming signal Sc.

  The converter circuit unit 3 is a general step-down chopper circuit, and includes a switching element Q1, a rectifying element D1, an inductor L1, and a smoothing capacitor C1.

  The smoothing capacitor C1 is connected to the LED module 12 in parallel. An inductor L1 is connected in series with this parallel connection. In addition, a diode D1 is connected in parallel to this parallel series circuit. The cathode terminal of the diode D1 is connected to the positive terminal of the DC power supply Vdc together with one end of the smoothing capacitor C1. The anode terminal of the diode D1 is connected to the other end of the capacitor C1 through the inductor L1.

  The switch element Q1 changes the current flowing through the inductor L1 by an on / off operation. The drain terminal of the switch element Q1 is connected to the anode terminal of the diode D1. The source terminal of the switch element Q1 is connected to the negative terminal of the DC power supply Vdc via the current detection resistor R1. The gate terminal of the switch element Q1 is connected to the converter control unit 4.

  Converter circuit unit 3 is not limited to a step-down chopper circuit. For example, it may be a buck-boost chopper circuit or a flyback converter circuit.

  The current detection resistor R1 is connected between the source terminal of the switch element Q1 and the negative terminal of the DC power supply Vdc.

  The current detection resistor R1 detects the current Is flowing through the inductor L1 when the switch element Q1 is on as the detection voltage Vfb. That is, the voltage applied to the current detection resistor R1 when the switch element Q1 is turned on is output to the converter control unit 4 as the detection voltage Vfb.

  The converter control unit 4 receives the dimming signal Sc output from the dimming control unit 5 and the detection voltage Vfb detected by the current detection resistor R1. Converter control unit 4 controls the off operation of switch element Q1 based on detection voltage Vfb and dimming signal Sc.

  The converter control unit 4 includes a comparator 6, a control logic 7, a zero voltage detection circuit (ZDC) 8, and a gate drive 9.

  The comparator 6 compares the dimming signal Sc with the detection voltage Vfb and outputs the comparison result to the control logic 7. That is, the comparator 6 outputs an H (high) level when the detection voltage Vfb reaches the dimming signal Sc.

  The zero voltage detection circuit 8 detects the voltage across the inductor L1 and outputs a zero voltage detection signal to the control logic 7 when the current flowing through the inductor L1 becomes zero.

  When the control logic 7 detects the zero voltage detection signal output from the zero voltage detection circuit (ZDC) 8, the control logic 7 switches the output signal from the L (low) level to the H level. On the other hand, when the detection voltage Vfb reaches the dimming signal Sc, the output signal is switched from the H level to the L level.

  A signal output from the control logic 7 is input to the gate drive 9. The gate drive 9 amplifies the output signal of the control logic 7 and outputs the PWM signal Sp to the gate terminal of the switch element Q1. That is, the switch element Q1 is turned on / off in response to the PWM signal Sp output from the gate drive 9 being input to the gate terminal.

  Thus, the converter control unit 4 turns on the switch element Q1 when the current flowing through the inductor L1 becomes zero, and turns off the switch element Q1 when the detection voltage Vfb reaches the dimming signal Sc. That is, as will be described later, converter control unit 4 controls the on / off operation of switch element Q1 so that a current flows through inductor L1 in a critical mode.

  [Description of Basic Operation of Light Source Driving Device 1]

  Hereinafter, the operation of the light source driving device 1 will be described assuming that the dimming signal Sc is 2.5V and the current detection resistance is 1Ω. Since the smoothing capacitor C1 is provided to suppress the ripple of the output current Io, it is ignored in the following description.

  When a DC voltage is applied from DC power supply Vdc and converter control unit 4 starts operating, switch element Q1 is turned on, and current Is flows from the positive electrode side of DC power supply Vdc. At this time, a gradually increasing current flows through a path that sequentially follows the LED module 12, the inductor L1, the switching element Q1, the current detection resistor R1, and the negative electrode side of the DC power supply Vdc. During the ON period of the switch element Q1, power is supplied from the DC power supply Vdc to the LED module 12, and energy is stored in the inductor L1.

  As the current flowing through the inductor L1 gradually increases, the current Is flowing through the switch element Q1 increases. When the current Is flowing through the switch element Q1 reaches 2.5A, the feedback voltage (detection voltage Vfb) detected by the current detection resistor R1 becomes 2.5V (= 1Ω × 2.5A) and is dimmed. The signal Sc is reached. Then, the comparator 6 operates and the control logic 7 turns off the switch element Q1. Thereby, the peak value of the current flowing through the switch element Q1 is controlled to be constant.

  When the switch element Q1 is turned off, a gradually decreasing current flows through a path that sequentially follows one end of the inductor L1, the diode D1, the LED module 12, and the other end of the inductor L1 due to the induced voltage of the inductor L1, and the energy of the inductor L1 is released. The

  At the timing when the voltage across the inductor L1 reaches 0V, the control logic 7 turns on the switch element Q1 again by the action of the zero voltage detection circuit (ZDC) 8.

  The converter control unit 4 performs the above-described control by outputting a PWM signal Sp (first PWM signal Sp1 described later) to the switch element Q1. The operation mode in which the switch element Q1 is turned on at the timing when the energy release of the inductor L1 is completed is called a critical mode.

  The operation that turns on the switch element Q1 before the energy discharge of the inductor L1 is completed is called a continuous mode, and the switch element Q1 is turned on after a rest period after the energy discharge of the inductor L1 is completed. Such an operation is called a discontinuous mode.

  The average value of the current flowing through the inductor L1 becomes the output current Io flowing through the LED module 12.

  In the critical mode, the current waveform of the inductor L1 is a triangular waveform, the current value at the beginning and end of each cycle is zero ampere, and the peak value is limited to a predetermined value. That is, it becomes a continuous triangular waveform starting from zero amperes every cycle, and the area of each triangle is constant. Therefore, the output current Io becomes a constant value that depends only on the set peak value of the inductor L1. The output current Io can be controlled by changing the set value of the peak value of the current Is of the inductor L1 in the dimming control. Further, the magnitude of the output current Io with respect to the peak value of the current Is of the inductor L1 is linear.

  In the discontinuous mode, the current waveform of the inductor L1 starts at zero ampere every time the switch element Q1 enters the ON period, and the peak value is limited to a predetermined value. In the off period, the current value decreases to zero ampere, and then passes through a zero ampere period (rest period) before moving on to the next on period. That is, the current waveform of the inductor L1 does not become a continuous triangular wave. Therefore, it is possible to control the output current Io by changing the set value of the peak value of the current Is of the inductor L1 in dimming control, but the magnitude of the output current Io with respect to the peak value of the current Is of the inductor L1. Becomes nonlinear.

  In the continuous mode, the peak value of the current waveform of the inductor L1 is limited to a predetermined value, but the current value at the beginning and end of each cycle is greater than zero amperes. That is, the current waveform of the inductor L1 is a continuous triangular waveform that does not become zero amperes, and the area in the waveform of each cycle is constant. Therefore, as in the critical mode, the output current Io becomes a constant value depending on the set peak value of the inductor L1. In the dimming control, the magnitude of the output current Io with respect to the peak value of the current Is of the inductor L1 is linear.

  In the present embodiment, instead of the operation in the critical mode, the operation in the continuous mode may be performed. The critical mode has higher power conversion efficiency than the continuous mode.

  [Explanation about light control]

  In the present embodiment, the dimming control unit 5 is a DC voltage dimming signal Vd2a having a voltage level corresponding to the on-duty of the dimming instruction signal Sad, according to the on-duty of the input dimming instruction signal Sad, Either a PWM dimming signal Vm having an upper voltage level constant and an on duty corresponding to the on duty of the dimming instruction signal Sad is generated as the dimming signal Sc.

  That is, as will be described later, when the on-duty of the dimming instruction signal Sad is equal to or greater than a predetermined value, the DC voltage dimming signal Vd2a is output to the drive circuit unit 2 as the dimming signal Sc. At this time, as the on-duty of the dimming instruction signal Sad increases, the voltage value of the dimming signal Sc increases and the output current Io increases.

  When the on-duty of the dimming instruction signal Sad is less than a predetermined value, the PWM dimming signal Vm is output to the drive circuit unit 2 as the dimming signal Sc. At this time, the smaller the on-duty of the dimming instruction signal Sad, the smaller the on-duty of the PWM dimming signal Vm, and the smaller the output current Io.

  FIG. 3 is a circuit diagram showing a configuration of the dimming control unit 5.

  As shown in FIG. 3, the dimming control unit 5 roughly includes a reference signal generation circuit 21, a DC voltage signal generation circuit 22, a PWM dimming signal generation circuit 23, a signal conversion circuit 24, and a DC voltage. A value limiting circuit 25 and a voltage dividing circuit 26 are included.

  The reference signal generation circuit 21 generates the reference signal Vb based on the dimming instruction signal Sad. In other words, the rising edge of the dimming instruction signal Sad is detected by a differentiating circuit constituted by the capacitor C11 and the resistor R11, and the switch element Q11 is turned on / off according to the detection signal Va. The switch element Q11 forms a sawtooth wave generation circuit together with the capacitor C12, the resistor R12, the operational amplifier OP1, and the reference power source Vref that is a DC voltage. At the timing when the switch element Q11 is turned on, the charging voltage of the capacitor C12 charged with the passage of time by the reference power source Vref is reset, so that a sawtooth wave signal having the same cycle as the dimming instruction signal Sad is generated as the reference signal Vb. Is generated as

  The DC voltage signal generation circuit 22 generates a second DC voltage signal Vc based on the reference signal Vb. That is, the divided signal Vb2 of the reference signal Vb is generated by the resistor R13 and the resistor R14. The peak value of the divided signal Vb2 is held by the peak hold circuit configured by the operational amplifier OP2, the rectifier element D11, and the capacitor C13, thereby generating the second DC voltage signal Vc.

  The signal conversion circuit 24 generates a first DC voltage signal Vd based on the dimming instruction signal Sad. That is, the first DC voltage signal Vd is generated based on the on-duty of the dimming instruction signal Sad by an integrating circuit composed of the resistor R17 and the capacitor C14.

  The PWM dimming signal generation circuit 23 generates the PWM dimming signal Vm based on the comparison result between the first DC voltage signal Vd and the reference signal Vb. That is, the voltage dividing signal Vb1 of the reference signal Vb is generated by the resistors R15 and R16. Then, the divided voltage signal Vb1 and the first DC voltage signal Vd are input to the operational amplifier OP3, and the on / off operation of the switch element Q12 is controlled by the output signal Ve of the operational amplifier OP3 as a comparison result. In this way, the PWM dimming signal Vm having the peak value of the divided voltage Vd2 (a divided voltage Vd2b described later) is generated.

  The DC voltage value limiting circuit 25 sets the lower limit voltage value of the first DC voltage signal Vd based on the second DC voltage signal Vc. DC power supply Vcc, transistor Q13, resistor R19, and resistor R20 constitute a first emitter follower circuit. DC power supply Vcc, transistor Q14, resistor R19, and resistor R20 constitute a second emitter follower. A circuit is configured.

  The first DC voltage signal Vd is input to the base terminal of the transistor Q13. Thereby, the emitter voltage Vd1a which is the output of the transistor Q13 becomes, for example, Vd1a = Vd−0.7V. On the other hand, the second DC voltage signal Vc is input to the base terminal of the transistor Q14. Thereby, the emitter voltage Vd1b which is the output of the transistor Q14 becomes, for example, Vd1b = Vc−0.7V. When Vd ≧ Vc, the first emitter follower circuit becomes dominant and the output Vd1 becomes Vd1a. On the other hand, when Vd <Vc, the second emitter follower circuit becomes dominant, and the output Vd1 becomes Vd1b. In other words, the lower limit voltage of the output Vd1 is limited to “Vc−0.7 V”.

  The voltage dividing circuit 26 includes a resistor R19 and a resistor R20. When the on-duty of the dimming instruction signal Sad is a predetermined value (for example, 30%) or more, the divided voltage Vd2a obtained by dividing the emitter voltage Vd1a from the DC voltage value limiting circuit 25 by the resistor R19 and the resistor R20 is adjusted. The light signal Sc is output to the drive circuit unit 2. On the other hand, when the on-duty of the dimming instruction signal Sad is less than a predetermined value, the PWM dimming signal Vm having the peak value of the divided voltage Vd2b obtained by dividing the emitter voltage Vd1b by the resistors R19 and R20 is dimmed. The signal Sc is output to the drive circuit unit 2. Note that the ratio of the resistance values of the resistors R19 and R20 is set to 1: 1, for example.

  FIG. 4 is a waveform diagram illustrating the dimming operation in the present embodiment.

  FIG. 4 shows a specific example in which the dimming control is performed from shallow dimming (upper limit value) to deep dimming (lower limit value). That is, in FIG. 4, the left side is shallow dimming, and the right side is deep dimming. Each row of (a) to (j) shows the waveform of each signal. The vertical axis is the voltage axis (or current axis), and the horizontal axis is the time axis.

  In the present embodiment, the upper limit value of the dimming signal Sc is, for example, 2.5 V (when the on-duty of the dimming instruction signal Sad is 100%). The lower limit value of the dimming signal Sc is, for example, 0.5 V (lower limit voltage value; when the on-duty of the dimming instruction signal Sad is 30% (an example of a predetermined value)). The lower limit value of the on-duty of the dimming instruction signal Sad is, for example, 1% (deepest dimming).

  As shown in FIG. 4, in the present embodiment, when the on-duty of the dimming instruction signal Sad is decreased from 100% to 1% (a), the output current Io is changed from I3 to I1. Decrease linearly (j).

  First, the first section in which the on-duty of the dimming instruction signal Sad is 30% or more (100% to 30%) will be described. When the on-duty of the dimming instruction signal Sad is decreased from 100% to 30% (a), the dimming signal Sc linearly decreases from 2.5 V to 0.5 V (h). In this first section, the divided voltage Vd2a (hereinafter, sometimes referred to as a DC voltage dimming signal Vd2a) is output as the dimming signal Sc. That is, when the on-duty of the dimming instruction signal Sad is 30% or more which is a predetermined value, the DC voltage dimming signal Vd2a corresponding to the first DC voltage signal Vd is output as the dimming signal Sc.

  Converter control unit 4 controls the peak current of inductor L1 using DC voltage dimming signal Vd2a as a reference value. That is, in the first section, the output current Io is controlled so as to correspond to the DC voltage dimming signal Vd2a.

  In the first section, the PWM signal Sp has a waveform with a higher switching frequency than the dimming instruction signal Sad (i). Therefore, in FIG. 4, it is displayed in black for convenience. The PWM signal Sp in the first section is referred to as a first PWM signal Sp1.

  In the first section, the current of the inductor L1 is set to a range that operates in the critical mode or the continuous mode. That is, when the on-duty of the dimming instruction signal Sad is 30% or more, the current of the inductor L1 is set to a range in which the operation is performed in the critical mode or the continuous mode. Thereby, the relationship of the output current Io with respect to the on-duty of the dimming instruction signal Sad becomes linear.

  Next, a second section in which the on-duty of the dimming instruction signal Sad is less than 30% (30% to 1%) will be described. In the second section, the dimming signal Sc is a PWM signal having the same frequency as the dimming instruction signal Sad and a peak value of 0.5 V (= high level) (h). As the on-duty of the instruction signal Sad is decreased from 30% to 1%, the on-duty of the PWM signal decreases accordingly. The dimming signal Sc in the second section is called a PWM dimming signal Vm.

  The converter control unit 4 controls the output current Io to zero when the PWM dimming signal Vm is at a low level. When the PWM dimming signal Vm is at a high level (0.5 V), the peak current of the inductor L1 is controlled using 0.5 V as a reference value. That is, the converter control unit 4 performs control so that the output current Io corresponds to 0.5V. Therefore, in this second section, the average value of the output current Io can be adjusted by performing intermittent control by changing the on-duty of the PWM dimming signal Vm. That is, the output current Io can be reduced by shortening the high level ratio (decreasing the on-duty).

  When the PWM dimming signal Vm is at a low level, the PWM signal Sp is at a low level (i). When the PWM dimming signal Vm is at a high level, the PWM signal Sp has a waveform with a switching frequency higher than that of the dimming instruction signal Sad (i). Therefore, in FIG. 4, the PWM signal Sp when the PWM dimming signal Vm is at a high level is displayed in black for convenience. That is, in the second section, the PWM signal Sp has a waveform with a high switching frequency determined by the converter control unit 4 during the ON time between the high level period and the synchronization of the PWM dimming signal Vm, and the PWM dimming signal Vm It becomes a low level during the OFF time between the low level period and the synchronization. The PWM signal Sp in the second section is referred to as a second PWM signal Sp2. The switch element Q1 intermittently performs an on / off operation based on the second PWM signal Sp2.

  When the on-duty of the dimming instruction signal Sad is lowered in the second section, the on-duty of the PWM dimming signal Vm is lowered. Thereby, the relationship of the output current Io with respect to the on-duty of the dimming instruction signal Sad becomes linear.

  When such a dimming operation is performed, the dimming control unit 5 operates as follows.

  The detection signal Va is a differential waveform of the dimming instruction signal Sad (b). That is, the voltage of the detection signal Va changes in synchronization with the rising edge or falling edge of the dimming instruction signal Sad. The switch element Q11 is turned on with a voltage synchronized with the rising edge.

  The reference signal generation circuit 21 generates a reference signal Vb having the same cycle as that of the dimming instruction signal Sad (c).

  The second DC voltage signal Vc is set to 1.7 V by the resistors R13 and R14 (d). That is, the reference signal Vb is divided by the voltage dividing ratio determined by the resistors R13 and R14, and the divided signal Vb2 is generated (d). Then, the second DC voltage signal Vc is set to 1.7 V, which is the same voltage value as the peak value of the divided signal Vb2, by the peak hold circuit.

  The peak value of the divided voltage signal Vb1 is set to 1.7 V by the resistors R15 and R16 (e). That is, it is set by dividing the reference signal Vb by a voltage dividing ratio determined by the resistors R15 and R16.

  The first DC voltage signal Vd is an integrated waveform of the dimming instruction signal. That is, when the on-duty of the dimming instruction signal Sad is decreased from 100% to 1%, the DC voltage signal Vd whose voltage value decreases linearly (e).

  The output signal Ve of the operational amplifier OP3 in the PWM dimming signal generation circuit 23 becomes high level when the first DC voltage signal Vd falls below the divided voltage signal Vb1 (f). That is, when the first DC voltage signal Vd is lowered linearly, the first DC voltage signal Vd falls below the peak value 1.7V of the divided signal Vb1. Then, the output signal Ve of the operational amplifier OP3 periodically falls below the first DC voltage signal Vd. The output signal Ve has a PWM waveform that becomes a high level when the first DC voltage signal Vd falls below the divided voltage signal Vb1.

  The output Vd1 of the DC voltage value limiting circuit 25 (the emitter voltage of the transistor Q13 or the transistor Q14) is linearly changed from 5V to 1V as the on-duty of the dimming instruction signal Sad is decreased from 100% to 30%. Go down. When the on-duty is less than 30%, 1V is maintained (g). That is, the lower limit voltage of the output Vd1 of the DC voltage value limiting circuit 25 is set to “Vc−0.7 V = 1.0 V”.

  The dimming signal Sc decreases linearly from 2.5 V to 0.5 V as the on-duty of the dimming instruction signal Sad decreases from 100% to 30% (DC voltage dimming signal (divided voltage) ) Vd2a). When the on-duty is decreased from 30% to 1%, the dimming signal Sc is switched to a PWM signal having a peak value of 0.5 V (= high level) (PWM dimming signal Vm). On-duty goes down.

  That is, when the on-duty of the dimming instruction signal Sad is 30% or more, the dimming signal Sc becomes a DC voltage dimming signal Vd2a obtained by dividing the output Vd1 of the DC voltage value limiting circuit 25 by the resistor R19 and the resistor R20. . On the other hand, when the on-duty of the dimming instruction signal Sad is less than 30%, the dimming signal Sc is the PWM dimming signal Vm. The PWM dimming signal Vm is a PWM signal whose peak value is a voltage Vd2b obtained by dividing the lower limit voltage 1V of the output Vd1 of the DC voltage value limiting circuit 25.

  FIG. 5 is a graph showing the relationship of the output current Io with respect to the on-duty of the dimming instruction signal Sad.

  In FIG. 5, the horizontal axis indicates the magnitude of the on-duty of the dimming instruction signal Sad, and the vertical axis indicates the magnitude of the output current Io.

  Conventionally, when the on-duty of the dimming instruction signal Sad is decreased from 100% to 1%, the current mode of the inductor L1 is switched to the discontinuous mode when the on-duty falls below a predetermined value (30%). There is a problem that the relationship between the on-duty of the dimming instruction signal Sad and the output current Io is switched from linear to non-linear.

  On the other hand, in the present embodiment, as shown in FIG. 5, even if the on-duty of the dimming instruction signal Sad falls below a predetermined value (30%), the above intermittent control is performed. The relationship between the on-duty of the dimming instruction signal Sad and the output current Io can be made linear (line BC).

  [Explanation of effects in the embodiment]

  As described above, in the present embodiment, the relationship between the dimming instruction signal magnitude and the output current magnitude can be controlled substantially linearly in a dimming area that is deeper than in the prior art.

  Moreover, the power conversion efficiency of the light source driving device can be improved by performing the switching operation in the critical mode. By improving the efficiency, the heat generation of the switch element Q1 can be reduced. Therefore, it is easy to reduce the size of the heat sink for heat dissipation and the light source driving device.

  In addition, since the dimming control unit can be configured with a simple analog circuit instead of an expensive microcomputer, the manufacturing cost of the light source driving device and the luminaire using the same can be reduced.

  [Others]

  FIG. 6 is a circuit diagram showing a modification of the DC voltage value limiting circuit.

  As shown in FIG. 6, instead of the DC voltage value limiting circuit 25 which is an emitter follower circuit as in the above-described embodiment, a DC voltage value limiting circuit 25a configured using two rectifier elements D21 and D22. May be used. The DC voltage value limiting circuit 25a is configured by replacing the transistor Q14 in the DC voltage value limiting circuit 25 with a rectifying element D22 and replacing the transistor Q13 with a rectifying element D21. Even if it is such a structure, the effect similar to the above can be acquired.

  The switch element Q1 is not limited to an N-channel MOS-FET, and may be a switch element having a similar function.

  The DC power supply and the drive circuit unit are not limited to those having the configuration as in the above embodiment. For example, an AC power source and an AC-DC converter may be combined.

  The value of the reference voltage, the value of the current detection resistor, the upper limit value of the dimming signal, the predetermined value, the lower limit value, the ratio of the resistance value, and the like in the above-described embodiment are specific examples, and are limited to the above. Not.

  The above embodiment should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Light source drive device 2 Drive circuit part 3 Converter circuit part 4 Converter control part 5 Dimming control part 12 LED module (an example of a light source)
21 Reference Signal Generation Circuit 22 DC Voltage Signal Generation Circuit 23 PWM Dimming Signal Generation Circuit 24 Signal Conversion Circuit 25 DC Voltage Value Limiting Circuit 80 Dimming Control Device C1 Smoothing Capacitor D1 Rectifier Element Io Output Current L1 Inductor Q1 Switch Element R1 Current Detection Resistor Sad Dimming instruction signal Sc Dimming signal Sp1 First PWM signal Sp2 Second PWM signal Vb Reference signal Vc Second DC voltage signal Vcc, Vdc DC power supply Vd First DC voltage signal Vd2a DC voltage dimming signal Vfb detection voltage Vm PWM dimming signal

Claims (5)

A light source driving device that drives a light source by supplying a current to a light source based on a dimming instruction signal that is a PWM signal,
A dimming control unit that outputs a dimming signal based on the dimming instruction signal;
A drive circuit unit for supplying a current to the light source based on the dimming signal,
The drive circuit unit is
A converter circuit unit including an inductor connected to the light source and a switch element that changes a current flowing through the inductor by an on / off operation;
A current detection resistor for detecting a current flowing through the inductor;
A converter control unit that controls the on / off operation of the switch element based on the detection result of the current detection resistor and the dimming signal;
The dimming controller is
When the on-duty of the dimming instruction signal is a predetermined value or more, a DC voltage dimming signal corresponding to the first DC voltage signal generated based on the dimming instruction signal is output as the dimming signal,
When the on-duty of the dimming instruction signal is less than a predetermined value, a PWM dimming signal having a peak value corresponding to the second DC voltage signal that is the predetermined value is generated based on the dimming instruction signal A light source driving device that outputs the PWM dimming signal as the dimming signal to the drive circuit unit. The converter controller is
When the DC voltage dimming signal is input as the dimming signal, a first PWM signal generated based on the DC voltage dimming signal is output to the switch element to turn on / off the switch element. Control
When the PWM dimming signal is input as the dimming signal, a second PWM signal generated based on the PWM dimming signal is output to the switch element, and the switch element intermittently turns on / off. The light source driving device according to claim 1, wherein the light source driving device is controlled to perform the following.   The light source driving device according to claim 1, wherein the converter control unit controls an on / off operation of the switch element so that a current flows through the inductor in a critical mode. The dimming controller is
A signal conversion circuit for generating the first DC voltage signal based on the dimming instruction signal;
A reference signal generation circuit for generating a reference signal based on the dimming instruction signal;
A PWM dimming signal generation circuit for generating the PWM dimming signal based on a comparison result between the first DC voltage signal and the reference signal;
A DC voltage signal generation circuit that generates the second DC voltage signal based on the reference signal;
4. The light source driving device according to claim 1, further comprising: a DC voltage value limiting circuit that sets a lower limit voltage value of the first DC voltage signal based on the second DC voltage signal. 5. A light source;
The light source driving device according to any one of claims 1 to 4, which drives the light source;
A lighting fixture comprising: a dimming control device that outputs the dimming instruction signal to the light source driving device.

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