JP5190390B2 - Light-emitting element lighting control device - Google Patents

Description

  The present invention relates to a light-emitting element lighting control device for lighting a light-emitting element such as an LED (light-emitting diode), and particularly suitable for dimming lighting of a light-emitting element by lighting pulse control in a vehicle headlamp or the like. The present invention relates to a light emitting element lighting control device.

  In general, LEDs as light emitting elements are characterized by high conversion efficiency from electricity to light, low power consumption, long life, and high reliability. Therefore, in recent years, demand for light sources of various lighting devices has been increasing. Is growing. In particular, when such an LED is used as a light source of a headlight and so-called DRL (Daylight Running Lights) is performed, the LED needs to be dimmed.

  By the way, the LED has a characteristic that chromaticity changes (color shift) depending on a current value. Therefore, if the direct current value supplied to the LED is simply decreased to reduce the lighting, color misregistration occurs. Therefore, in order to suppress such color misregistration, the current is kept constant and the luminance is changed with the pulse width. It is desirable to perform lighting pulse control for adjusting the above.

  Therefore, as a method of dimming and lighting an LED while suppressing color misregistration, in the conventional technology, a switching wave element such as a MOSFET connected in series with the LED is turned on / off to produce a rectangular wave lighting pulse current to the LED. There has been proposed a method for controlling the lighting pulse by flowing it (for example, see Patent Document 1 below).

JP 2008-181969 A

  By the way, in the case of providing a dedicated switching element such as a MOSFET for flowing a rectangular wave lighting pulse current to the LED in order to perform dimming lighting as in the prior art described in Patent Document 1, the number of parts is reduced. There is a problem that the cost increases as the size increases and the size increases.

  Also, instead of connecting a switching element such as a MOSFET in series with the LED, for example, in a switching power supply circuit that supplies current to the LED, the lighting pulse current is supplied to the LED by controlling on / off of the switching element constituting the circuit. There is also a method of flowing. However, in that case, the rising and falling speed of the lighting pulse current supplied to the LED is slow, the waveform is distorted and a rectangular pulse with a short pulse width cannot be produced, or the lighting pulse current waveform becomes trapezoidal. There was a problem to do. When the lighting pulse control of the LED is performed in this way, if the waveform of the lighting pulse current deviates from the rectangular wave, there arises a problem that a color shift occurs even though the lighting pulse control is performed.

  The present invention has been made to solve the above-described problems, and is capable of supplying a light-emitting element with a lighting pulse current that is small in size, low in cost, and has a fast rising and falling speed. An object of the present invention is to provide a light emitting element lighting control device capable of suppressing the occurrence of flickering.

  In order to achieve the above object, in the present invention, a lighting pulse current is supplied to the light emitting element based on a lighting pulse control signal that periodically repeats an ON command and an OFF command for the light emitting element. In the light emitting element lighting control device for dimming lighting, the following configuration is adopted.

  That is, in the present invention, the switching power supply circuit in which the lighting pulse current is controlled by the duty ratio of the drive signal for driving the switching element or the conduction time in one cycle, and the lighting pulse current output from the switching power supply circuit are detected. The lighting pulse by changing the duty ratio or the conduction time of the drive signal applied to the switching element during the ON command period of the lighting pulse control signal according to the current detection value by the current detection means and the current detection value by the current detection means A control means for controlling the current, wherein the control means has a first time until the current detection value by the current detection means exceeds a predetermined current threshold after the lighting pulse control signal changes from the OFF command to the ON command. The period T1 of 1 has the duty ratio or the conduction time of the drive signal as a maximum value, After the elapse of the first period T1, the duty period of the drive signal is set so that the current detection value gradually approaches a predetermined target current value during a second period T2 until the lighting pulse control signal becomes an OFF command state. Alternatively, in the third period T3 in which the conduction time is feedback-controlled and the lighting pulse control signal is in the off command state, the duty ratio of the driving signal or the conduction time is set to zero. It is said.

  According to the present invention, the duty ratio or conduction time of the drive signal for driving the switching element constituting the switching power supply circuit is maximized in the first stage of the ON command state of the lighting pulse control signal for lighting the light emitting element. Therefore, the rise of the lighting pulse current output from the switching power supply circuit can be made steep. Further, the duty ratio or conduction time of the drive signal is set to zero during the OFF command state of the lighting pulse control signal, so that the falling of the lighting pulse current can be made steep. Thereby, a pulse current close to a rectangular wave can be supplied to the light emitting element. Therefore, since the ratio of the flat portion between the rise and fall of the lighting pulse current is large, the light emitting element can emit light in a state closer to a constant current, and the color shift of the light emitting element can be suppressed. .

  In addition, since the rise and fall of the lighting pulse current can be made steep, it is possible to supply a narrower pulse waveform current. When the repetition frequency of the lighting pulse current is constant, the luminance of the light emitting element is reduced. The adjustment range can be widened. In addition, since it is possible to set a high repetition frequency when performing the pulse width control of the lighting pulse current, flickering of the light emitting element can be reduced. In addition, in order to obtain such characteristics, it is not necessary to use an extra switching element for on / off control of the light emitting element as in the prior art, so that the apparatus can be realized in a small size and at low cost. Become.

It is a circuit block diagram of the light emitting element lighting control apparatus in Embodiment 1 of this invention. It is a timing chart which shows operation | movement of the light emitting element lighting control apparatus. It is a circuit block diagram of the light emitting element lighting control apparatus in Embodiment 2 of this invention. It is a timing chart which shows operation | movement of the light emitting element lighting control apparatus. It is a circuit block diagram of the light emitting element lighting control apparatus in Embodiment 3 of this invention. It is a timing chart which shows operation | movement of the light emitting element lighting control apparatus.

Embodiment 1 FIG.
FIG. 1 is a circuit configuration diagram of the light-emitting element lighting control device according to Embodiment 1 of the present invention.
In the light emitting element lighting control device 1 according to the first embodiment, a switching power supply circuit 4 is provided between a DC power supply 2 and an LED 3 as a light emitting element.

  The switching power supply circuit 4 is of a so-called step-down chopper type in this example, and includes a switching element 41 such as an FET or IGBT, a rectifying element 42 such as a diode, and a reactor 43. And this switching power supply circuit 4 repeats on / off of the switching element 41 periodically by a drive signal Sg applied to the gate of the switching element 41 from the control circuit 10 to be described later. That is, the output voltage value and the output current value are controlled.

  Note that the switching power supply circuit 4 is not limited to the step-down chopper type as in this example, and other switching power supply circuit systems, for example, circuit systems such as a boost chopper, a flyback converter, and a forward converter are used. It is possible to apply things.

  Further, the light emitting element lighting control device 1 includes a current detector 5 and a control circuit 10. The current detector 5 corresponds to the current detection means in the claims and is connected to the output terminal of the switching power supply circuit 4 to detect the lighting pulse current Iout flowing through the LED 3 as a load. As the current detector 5 in this case, a general current detection circuit using a shunt resistor or a Hall element can be applied.

  The control circuit 10 corresponds to the control means in the claims, and performs switching during the ON state of the lighting pulse control signal Sc based on the current detection value Id by the current detector 5 and the lighting pulse control signal Sc. The lighting pulse current Iout is controlled by changing the duty ratio of the drive signal Sg applied to the element 41.

  The lighting pulse control signal Sc in this case is a digital signal for dimming and lighting the LED 3 by periodically repeating an on (lighting) command and an off (non-lighting) command of the LED 3. When the signal Sc is at a high level, the LED 3 is on, and when the signal Sc is at a low level, the LED 3 is off. Here, the lighting pulse control signal Sc is given from the outside as shown in FIG. 1, but the present invention is not limited to this. For example, the lighting pulse control signal Sc can also be generated inside the control circuit 10. In this case, the ON / OFF command duty ratio of the lighting pulse control signal Sc can be arbitrarily adjusted by, for example, an external volume.

Next, details of the configuration of the control circuit 10 will be described.
This control circuit 10 compares a current detection value Id obtained by detecting the lighting pulse current Iout with the current detector 5 and a preset target current value Io, and outputs the difference between them as a current error signal. 101, a PI (proportional integration) controller 102 as a proportional integration means for proportionally integrating the current error signal output from the subtractor 101, an output of the PI controller 102 and a preset maximum duty ratio. A resector 103 that selects one and outputs it as a duty ratio command signal Sdr, a PWM signal generator 104 that generates a PWM signal having a predetermined duty ratio based on the duty ratio command signal Sdr given from the resector 103, and a lighting pulse control The PWM signal generator 104 is allowed to pass a PWM signal during a period when the signal Sc is on (high level). Ndogeto 105, and in addition to the gate of the switching element 41 comprises a gate drive circuit 106 for switching operation as an amplifier to drive signal Sg output from the AND gate 105.

  Then, the current detector 5, the subtractor 101, the PI controller 102, and the selector 103 control the duty ratio of the drive signal Sg, thereby feedback controlling the lighting pulse current Iout output from the switching power supply circuit 4. The route is configured. As the PWM signal generator 104, for example, a triangular wave generator is provided, and the slice level of the triangular wave generated from the triangular wave generator is set by the duty ratio command signal Sdr given from the selector 103.

  Further, the control circuit 10 includes an edge detector 107 that detects a rising edge of the lighting pulse control signal Sc, a current detection value Id of the lighting pulse current Iout detected by the current detector 5, and a preset current threshold value Ish. When the current detection value Id exceeds the current threshold value Ish (Id ≧ Ish), the comparator 108 that outputs a high level signal is set by the output of the edge detector 107 and reset by the output of the comparator 108 Flip-flop 109, inverter 110 that inverts the level of the lighting pulse control signal Sc, and a hold signal that holds the high-level output of the inverter 110 and the high-level output of the flip-flop 109 for the PI controller 102. An OR gate 111 for outputting as Sho is provided.

  When the flip flip 109 is set and the output Sf becomes high level, the selector 103 selects a preset maximum duty ratio value and outputs it as the duty ratio command signal Sdr. When the flip flip 109 is reset and its output Sf becomes low level, the output of the PI controller 102 is selected and output as the duty ratio command signal Sdr. In the first embodiment, the current threshold Ish in the comparator 108 is set in advance so as to be the same value (Ish = Io) as the target current value Io in the current feedback control.

  Next, the operation of the light-emitting element lighting control circuit 1 having the above configuration will be described with reference to timing charts shown in FIGS.

  As described above, the lighting pulse control signal Sc given to the control circuit 10 from the outside is a digital signal that gives an LED3 on (lighting) command at a high level and an LED3 off (non-lighting) command at a low level as described above. The on / off frequency of the lighting pulse control signal Sc at this time is set to at least the visual critical fusion frequency (50 Hz to 100 Hz) or more so as not to feel flicker.

  Here, when the lighting pulse control signal Sc rises from low level to high level at time t1, the rising edge is detected by the edge detector 107, and the flip-flop 109 is set by a trigger signal based on the edge detection. As a result, the output Sf of the flip-flop 109 becomes high level. In response to this, the selector 103 selects a preset maximum value of the duty ratio. Here, as the maximum value of the duty ratio selected by the selector 103, the duty ratio may be 1, that is, the switching element 41 may be kept in a conductive state. However, the current of the reactor 43 increases excessively and the reactor 43 is saturated. There is a risk of doing. In order to prevent this, in this example, the maximum value of the duty ratio is limited to 0.9, for example. Note that the maximum value of the duty ratio is not necessarily limited to this value.

  The maximum value of the duty ratio selected by the selector 103 is given to the PWM signal generator 104 as the duty ratio command signal Sdr. Therefore, the PWM signal output from the PWM signal generator 104 has a duty ratio (= Tb / Ta) of a maximum value (0.9 in this example) as shown in the upper diagram of FIG. Become. Then, the PWM signal having the maximum duty ratio is applied to the AND gate 105. At this time, since the high level lighting pulse control signal Sc is given to the AND gate 105, the PWM signal having the maximum duty ratio is driven by the gate. The drive signal Sg is applied to the gate of the switching element 41 via the circuit 106. For this reason, the lighting pulse current Iout output from the switching power supply circuit 4 rapidly increases.

  Next, when the current detection value Id of the lighting pulse current Iout detected by the current detector 6 exceeds a predetermined current threshold value Ish (= Io) at time t2 after the period T1 has elapsed, the comparator 18 As a result, the flip-flop 109 is reset and its output Sf becomes low level. Accordingly, the selector 103 selects the output of the PI controller 102, and this is sent to the PWM signal generator 102 as the duty ratio command signal Sdr. Given. Therefore, the duty ratio (= Tb / Ta) of the PWM signal output from the PWM signal generator 104 is controlled based on the output of the PI controller 102 as shown in the lower diagram of FIG. The

  That is, after time t2, feedback control is performed so that the lighting pulse current Iout output from the switching power supply circuit 4 gradually approaches the target current value Io by the original feedback path. In this case, since the current threshold value Ish is set in advance to the same value as the target current value Io in the feedback control, when the current detection value Id gradually increases and reaches the target current value Io, the target current value is maintained as it is. Io can be maintained.

  Next, when the time t3 is reached after the period T2 has elapsed, the lighting pulse control signal Sc is in a low level (off command) state. Then, since the output of the PWM signal is forcibly cut off by the AND gate 105, the duty ratio of the drive signal Sg applied to the switching element 41 becomes zero. As a result, the lighting pulse current Iout output from the switching power supply circuit 4 rapidly decreases and eventually becomes zero. This state is continued until the time t4 when the lighting pulse control signal Sc next rises from the low level to the high level.

  Thereafter, the period from time t4 to t5 is the same as the period T1 from time t1 to t2 (hereinafter referred to as the maximum duty ratio period), and the period from time t5 to t6 is the period T2 from time t2 to t3 ( Hereinafter, the period from time t6 to t7 is the same as the period T3 from time t3 to t4 (hereinafter referred to as zero duty ratio period), and the same operation is repeated. In this way, the entire period (= T1 + T2 + T3) of the maximum duty ratio period T1, the current feedback control period T2, and the duty ratio zero period T3 is set to one cycle that is the same as the lighting pulse control signal Sc, and is synchronized with the lighting pulse control signal Sc. By repeating this, the lighting pulse current Iout can be supplied to the LED 3 so as to be dimmed. The first period in the claims corresponds to the maximum duty ratio period T1, the second period corresponds to the current feedback control period T2, and the third period corresponds to the zero duty ratio period T3.

  Here, focusing on the period Tx from time t3 to time t5, the duty ratio of the PWM signal output from the PWM signal generator 104 is forcibly controlled to the maximum value or controlled to zero in this period Tx. Therefore, during the period Tx, the lighting pulse current Iout output from the switching power supply circuit 4 has a value significantly different from the target current value Io. Therefore, if this is left unattended, the error signal of the subtractor 101 becomes very large and the integral term in the PI controller 102 integrates the error signal. For example, at time t5, the selector 103 causes the PI controller 1102 to When the output is selected, the duty ratio commanded by the duty ratio command signal Sdr is greatly different from the duty ratio value corresponding to the target current value Io. As a result, the lighting output from the switching power supply circuit 4 is performed. The pulse current Iout may be large and cause hunting.

  Therefore, here, during the period Tx from time t3 to time t5, when the output of the OR gate 111 rises, this is given as a hold signal Sho to the PI controller 102, and the PI controller 102 at time t3 The integral term is kept (held) as it is until time t5 is reached. In this way, when the feedback control is resumed at time t5, the value of the integral term of the PI controller 102 is the same as the state at time t3 when the lighting pulse current Iout from the switching power supply circuit 4 is stable. Therefore, the lighting pulse current Iout can be quickly converged to the target current value Io, and the hunting of the lighting pulse current Iout can be suppressed.

  In this case, in order to hold the integral term of the PI controller 102, for example, the register (not shown) for computing the integral term is not operated during the period Tx from time t3 to t5, The integration term value can be temporarily saved in the memory at time t3, and the saved integration term value can be read from the register at time t5.

  As described above, the light-emitting element lighting control device 1 according to the first embodiment drives the switching element 41 at the first stage during the ON command state of the lighting pulse control signal Sc for lighting the LED 3. Since the duty ratio of Sg is maximized, the rise of the lighting pulse current Iout output from the switching power supply circuit 4 can be made steep. Further, since the duty ratio of the drive signal Sg is made zero during the period of the turn-off command state of the lighting pulse control signal Sc, the falling of the lighting pulse current Iout can be made steep. Thereby, a pulse current close to a rectangular wave can be supplied to the LED 3. Therefore, since the ratio of the flat portion between the rising and falling of the lighting pulse current Iout increases, the LED 3 can emit light in a state closer to a constant current, and the color shift of the LED 3 can be suppressed. .

  Further, since the rise and fall of the lighting pulse current Iout can be made steep, it is possible to supply a narrower pulse waveform current. When the repetition frequency of the lighting pulse current Iout is constant, the brightness of the LED 3 The adjustment range can be widened. Moreover, since it becomes possible to set the repetition frequency at the time of performing pulse width control high, the flicker of LED3 can be decreased. In addition, in order to obtain such characteristics, there is no need to use an extra switching element for on / off control of the LED 3 as in the prior art, so that the apparatus can be miniaturized and realized at low cost. It becomes possible.

Embodiment 2. FIG.
FIG. 3 is a circuit configuration diagram of the light-emitting element lighting control device according to the second embodiment of the present invention, and components corresponding to or corresponding to those of the first embodiment shown in FIG.

  In the first embodiment, the current threshold value Ish that defines the end point of the maximum duty ratio period T1 is the same as the target current value Io (Ish = Io). However, when an integration element such as a capacitor is inserted in the output of the switching power supply circuit 4, the current increases due to the integration effect of the capacitor even when the duty ratio maximum period T1 shifts to the next current feedback control period T2. May not stop, and an overshoot may occur in the lighting pulse current Iout output from the switching power supply circuit 4. Therefore, in the second embodiment, the current threshold Ish is feedback-controlled so that the occurrence of overshoot can be suppressed within a short period of time.

  That is, in the light emitting element lighting control device 1 according to the second embodiment, an output capacitor for removing a current ripple included in the lighting pulse current Iout due to the switching operation of the switching element 41 on the output side of the switching power supply circuit 4. A low-pass filter 7 composed of 71 is inserted, and a current detector 6 is provided on the output side of the low-pass filter 7.

  Further, in the second embodiment, in order to suppress the overshoot of the lighting pulse current Iout when the integration element of the output capacitor 71 is inserted, in addition to the configuration of the first embodiment, it is detected by the current detector 6. A peak hold circuit 112 for detecting and holding the maximum value of the current detection value Id, and an S / H (sample hold) circuit 113 for sampling and holding the maximum value of the current detection value Id held by the peak hold circuit 112. The subtractor 114 that compares the output value of the S / H circuit 113 and the target current value Io and outputs the difference between the two as a threshold error signal, and the threshold error signal output from the subtractor 114 is proportionally integrated. A PI controller 115 is newly provided that gives a value to the comparator 108 as a current threshold Ish. The peak hold circuit 112 corresponds to the peak value detection means in the claims, and the current threshold control means in the claims is defined by the S / H circuit 113, the subtractor 114, and the PI controller 115. It is configured.

  In this case, every time the edge detector 107 detects the rise timing of the ON command of the lighting pulse control signal Sc, that is, the beginning of each cycle, the peak hold circuit 112 is reset and S / H (sample hold ) The circuit 113 samples and holds the peak value of the current detection value Id held by the peak hold circuit 112.

  Next, the operation of the light emitting element lighting control device having the above configuration will be described with reference to a timing chart shown in FIG.

  In the initial stage when the lighting pulse control is started, the peak value of the current detection value Id detected by the current detector 6 and held by the peak hold circuit 112 becomes higher than the target current value Io, and overshoot occurs. At this time, since the threshold error signal obtained by the subtractor 114 also increases, the current threshold Ish obtained by the PI controller 115 is also set relatively high in the initial stage of lighting control. As a result, the timing at which the flip-flop 109 is reset is earlier than when the current threshold value Ish is fixed to a low constant value in advance. When the timing at which the flip-flop 109 is reset is advanced, the length of the maximum duty ratio period T1 is shortened, and the current feedback control period T2 is switched at an early timing. For this reason, an increase in the lighting pulse current Iout can be suppressed.

  When the above feedback control is repeated in synchronization with the lighting pulse control signal Sc, the current threshold Ish obtained by the PI controller 115 gradually decreases with time, and the flip-flop 109 is reset with this. Will also get faster. As a result, the length of the duty ratio maximum period T1 is gradually shortened with the passage of time, and can be switched to the current feedback control period T2 at an early timing. That is, in FIG. 4, assuming that the maximum duty ratio period from time t1 to t2 is T1a, the maximum duty ratio period from time t4 to t5 is T1b, and the maximum duty ratio period from time t7 to t8 is T1c, T1a> T1b> T1c Become. Thereby, the overshoot of the lighting pulse current Iout is suppressed within a short time.

As described above, in the second embodiment, even when the low-pass filter 7 having an integration element such as the capacitor 71 is provided on the output side of the switching power supply circuit 4, the LED 3 rises and falls quickly and overshoots. It is possible to supply the lighting pulse current Iout with less chute and closer to a rectangular wave. Further, the ripple current flowing in the LED 3 can be suppressed by the effect of the low-pass filter 7.
Since other configurations and operations are the same as those in the first embodiment, detailed description thereof is omitted here.

Embodiment 3 FIG.
FIG. 5 is a circuit configuration diagram of the light-emitting element lighting control device according to Embodiment 3 of the present invention, and components corresponding to or corresponding to Embodiment 1 shown in FIG.

  In the third embodiment, as in the second embodiment, even when the low-pass filter 7 having an integration element such as the output capacitor 71 is provided on the output side of the switching power supply circuit 4, the overshoot is small and the rectangular wave is generated. A near lighting pulse current Iout is obtained.

  That is, in the light emitting element lighting control device 1 according to the third embodiment, an output capacitor for removing a current ripple included in the lighting pulse current Iout due to the switching operation of the switching element 41 on the output side of the switching power supply circuit 4. A low-pass filter 7 consisting of 71 is inserted. Further, a current detector (referred to as a first current detector here) 5 for detecting a lighting pulse current output from the switching power supply circuit 4 is provided between the switching power supply circuit 4 and the low-pass filter 7, Between the output side of the low-pass filter 7 and the LED 3, a current detector (referred to as a second current detector here) 6 that detects the lighting pulse current that has passed through the low-pass filter 7 is provided. The detection output of the first current detector 5 is supplied to the comparator 108, and the detection output of the second current detector 6 is supplied to the subtractor 101.

  Next, the operation of the light emitting element lighting control device having the above-described configuration will be described with reference to a timing chart shown in FIG.

  In the maximum duty ratio period T1, the current detection value Id1 by the first current detector 5 that directly detects the lighting pulse current Iout before passing through the low-pass filter 7 detects the lighting pulse current Iout after passing through the low-pass filter 7. The current rises faster than the current detection value Id2 of the second current detector 6. For this reason, the current detection value Id1 by the first current detector 5 reaches the current threshold value Ish earlier than the current detection value Id2 of the second current detector 6.

  Then, when the current detection value Id1 by the first current detector 5 exceeds the current threshold value Ish (= Io) (time t2), the selector 103 switches the connection to the PI controller 102 side. The maximum duty ratio control period T1 is switched to the current feedback control period T2 in which the lighting pulse current is feedback-controlled. At this time, although the value of the lighting pulse current Iout has not yet reached the target current value Io, the control circuit 10 determines that the current detection value Id2 by the second current detection means 6 is a predetermined target value during the current feedback control period T2. Since the feedback control is performed so as to approach the current value Io, the lighting pulse current Iout reaches the current target value Io after a delay due to the integration effect of the low-pass filter 7. At that time, since switching to current feedback control has already been performed and the duty ratio of the switching power supply circuit 4 has decreased, overshooting of the lighting pulse current Iout is suppressed.

As described above, in the third embodiment, it is detected that the current detection value Id1 of the first current detector 5 provided between the switching power supply circuit 4 and the low-pass filter 7 exceeds the current threshold value Ish. Therefore, even when the low-pass filter 7 having an integration element such as the capacitor 71 is provided on the output side of the switching power supply circuit 4, the LED 3 rises and falls quickly and has little overshoot. A lighting pulse current Iout closer to a rectangular wave can be supplied. Further, the ripple current flowing in the LED 3 can be suppressed by the effect of the low-pass filter 7.
Since other configurations and operations are the same as those in the first embodiment, detailed description thereof is omitted here.

  In the first to third embodiments, the output electric quantity of the switching power supply circuit 4 is controlled by controlling the duty ratio of the PWM signal output from the PWM signal generator 104 when the lighting pulse control signal Sc is in the ON command state. However, in the switching converter system generally called a quasi-resonant type, the repetition period includes a resonance period, and the repetition period of conduction / non-conduction varies depending on various conditions such as input / output voltage. Therefore, in such a case, it is more appropriate to consider that the output electricity quantity is controlled by the conduction time of the switching element 41 rather than controlling the output electricity quantity by the duty ratio. The present invention can be applied. In this case, the maximum duty ratio can be read as the maximum conduction time, and the zero duty ratio can be read as the conduction time is zero.

  In the first to third embodiments, the case where the PI controller 102 is configured by a digital circuit such as a DSP or a logic circuit has been described. However, the present invention is not limited to this, and for example, PI control A proportional integrator using an operational amplifier is used as the unit 102, an analog switch is provided on the input side of the proportional integrator, and a period from the previous current feedback control period T2 to the transition to the next current feedback control period T2 It is also possible to adopt a configuration in which the analog switch is turned off by the hold signal Sho given to Tx. At this time, if the input impedance of the operational amplifier is sufficiently high, the charge of the integrating capacitor is held, and therefore, the integral term can be held over the period Tx.

  In the first to third embodiments, the control circuit 10 is configured by hardware combining logic circuits. However, the present invention is not limited to this. For example, a predetermined control program is installed in the microcomputer. It is also possible to configure by software.

  The light-emitting element lighting control device 1 of the above-described first to third embodiments is based on the premise that the LED 3 as the light-emitting element is dimmed by lighting pulse control in a vehicle headlamp or the like. In the case where an LD (laser diode) is used as a light emitting element in a display device, the present invention can also be applied to the case where the LD is controlled by dimming.

1 light emitting element lighting control device, 3 LED (light emitting element), 4 switching power supply circuit,
41 switching element, 5 current detector (first current detector),
6 Current detector (second current detector), 7 Low-pass filter,
10 control circuit (control means), 102 PI controller (proportional integration means),
112 peak hold circuit (maximum value detection means), 113 S / H circuit,
114 subtractor, 115 PI controller, Iout lighting pulse current,
Id, Id1, Id2 current detection value, Io target current value, Ish current threshold value,
Sc lighting pulse control signal, Sg drive signal,
T1 duty ratio maximum period (first period),
T2 current feedback control period (second period),
T3 Duty ratio zero period (third period).

Claims (5)

A light emitting element lighting control device for dimming lighting the light emitting element by passing a lighting pulse current to the light emitting element based on a lighting pulse control signal that periodically repeats an on command and an off command for the light emitting element,
A switching power supply circuit in which the lighting pulse current is controlled by the duty ratio of the drive signal for driving the switching element or the conduction time in one cycle, current detection means for detecting the lighting pulse current output from the switching power supply circuit, and Control means for controlling the lighting pulse current by changing the duty ratio or the conduction time of the drive signal applied to the switching element during the ON command period of the lighting pulse control signal according to the current detection value by the current detection means And
In the first period T1 from when the lighting pulse control signal changes from the off command to the on command, the current detection value by the current detection unit exceeds a predetermined current threshold value. The duty ratio or the conduction time is set to the maximum value, and after the elapse of the first period T1, the current detection value is a predetermined value during a second period T2 until the lighting pulse control signal is in the off command state. The duty ratio of the drive signal or the conduction time is feedback-controlled so as to approach the target current value, and the third period T3 in which the lighting pulse control signal is in the off command state is the duty ratio of the drive signal or A light emitting element lighting control device characterized in that the conduction time is zero. The control means includes proportional integration means in the feedback control loop, and the proportional integration means is from the last time of the second period T2 to the first time of the second period T2 in the next cycle. The light-emitting element lighting device according to claim 1, wherein the light-emitting element lighting device holds an integral term. The light emitting element lighting control device according to claim 1, wherein the current threshold value and the target current value are the same predetermined value. The control means includes a peak value detection means for detecting a peak value of the current detection value, and a current threshold control means for feedback-controlling the current threshold so that the peak value gradually approaches the target current value. The light-emitting element lighting control device according to claim 1 or 2. A low pass filter is connected between the output side of the switching power supply circuit and the light emitting element, and when the current detector is a first current detector, in addition to this, after passing through the low pass filter In the second period T2, the control means includes second current detection means for detecting a lighting pulse current, instead of the current detection value from the first current detector. 4. The feedback control of the duty ratio or conduction time of the drive signal so that the current detection value by the detection means gradually approaches a predetermined target current value. 2. The light-emitting element lighting control device according to item 1.

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