JP2020072123A - Semiconductor light source drive device - Google Patents

Abstract

To provide a semiconductor light source drive device that has a small loss and a low breakage risk of a semiconductor light source when a time period in which a laser light source is driven and controlled so that PWM modulation of optical output is performed and a long OFF time period coexist.SOLUTION: A semiconductor light source drive device comprises: a switching power supply; a semiconductor light source that emits light by being applied with a current; and a light source feedback unit that outputs such a target current value that a variable of the semiconductor light source is accorded with a target value for the variable on the basis of the variable. The semiconductor light source drive device controls the switching power supply so that the current flowing in the semiconductor light source is accorded with the target current value, and performs PWM modulation of output light of the semiconductor light source in a time period except a periodic idle time period having a first time width where no current is applied to the semiconductor light source. In the semiconductor light source drive device, a temperature of the semiconductor light source is gradually increased in a rising time period having a predetermined second time width immediately after the idle time period.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a semiconductor light source driving device that PWM-modulates and adjusts the output of a semiconductor light emitting element.

  Patent Document 1 discloses a semiconductor light source drive device capable of driving while maintaining a peak of a drive current of a laser light source constant during a period in which PWM modulation is performed and a period in which PWM modulation is not performed. This semiconductor light source driving device compares the average of the optical output of the laser light source detected by the photosensor with the average value of the signal for controlling the drive current of the laser light source, and performs feedback so that they are equal. As a result, the average value of the current flowing through the laser light source can be driven while keeping the peak of the drive current of the laser light source constant during the period in which the PWM modulation is performed and the period in which the PWM modulation is not performed.

JP, 7-154016, A

  The present disclosure provides a semiconductor light source driving device that has a small loss and a small risk of damage when a period for driving and controlling a semiconductor light source so that a light output is PWM-modulated and a long off period are mixed.

  A semiconductor light source drive device according to the present disclosure outputs a target current value based on a switching power supply, a semiconductor light source that emits light by passing a current, and a variable of the semiconductor light source, such that the variable matches a target value of the variable. And a light source feedback section for controlling the switching power supply so that the current flowing through the semiconductor light source matches the target current value, and excluding the periodic pause period having a first time width during which no current flows through the semiconductor light source. In the semiconductor light source driving device that PWM-modulates the output light of the semiconductor light source by the method described above, the temperature of the semiconductor light source is gradually increased in the rising period having the predetermined second time width immediately after the pause period.

  According to the semiconductor light source drive device according to the present disclosure, when a period for driving and controlling the semiconductor light source so that the light output is PWM-modulated and a long rest period are mixed, the loss is small and the risk of damage to the semiconductor light source is low. Is also low.

Block diagram showing a configuration example of the semiconductor light source driving device 10 according to the first embodiment Timing chart showing waveforms of drive control signals and the like in each part of the semiconductor light source drive device 10 of FIG. Block diagram showing a configuration example of a semiconductor light source driving device 10A according to the second embodiment Timing chart showing waveforms of drive control signals and the like in each part of the semiconductor light source drive device 10A of FIG. Block diagram showing a configuration example of a semiconductor light source driving device 10B according to the third embodiment Block diagram showing a configuration example of a semiconductor light source driving device 10C according to the fourth embodiment

  Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed description than necessary may be omitted. For example, detailed description of well-known matters and duplicate description of substantially the same configuration may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art.

  The inventor provides the accompanying drawings and the following description in order for those skilled in the art to fully understand the present disclosure, and is not intended to limit the subject matter described in the claims by these. Absent.

(Embodiment 1)
Hereinafter, the first embodiment will be described with reference to FIGS. 1 and 2.

[1-1. Constitution]
FIG. 1 is a block diagram showing a configuration example of a semiconductor light source driving device 10 according to the first embodiment. In FIG. 1, the semiconductor light source driving device 10 includes a switching power supply 100, a semiconductor light source 110, a light source feedback unit 120, a current value comparator 125, a current switching unit 130, a detection resistor 140, a sampling switch 150, a detection voltage averaging circuit 160, A PWM modulator 170, a rising control circuit 180, and an AND gate 190 are provided. The light source feedback unit 120 includes a photo sensor 121, a sampling switch 122, a light source intensity averaging circuit 123, and a light source intensity comparator 124. The current switching unit 130 includes an operational amplifier 131, a first FET 132, and a second FET 133.

  In FIG. 1, the switching power supply 100 is controlled by the comparison result signal input from the current value comparator 125, and supplies power to the semiconductor light source 110 so that the current flowing through the semiconductor light source 110 matches the target current value. The semiconductor light source 110 is composed of, for example, a laser diode or the like, emits light by passing a current, and outputs light to the outside.

  The first FET 132 analog-controls the current flowing through the semiconductor light source 110 according to the rising control signal amplified by the operational amplifier 131. Here, the larger the value of the rising control signal, the larger the current flowing through the semiconductor light source 110, and when the value of the rising control signal is at the high level, the first FET 132 conducts all the current. On the other hand, the smaller the value of the rising control signal is, the smaller the current flowing through the semiconductor light source 110 is. When the value of the rising control signal is low level, the first FET 132 does not flow the current. The second FET 133 controls on / off of the current flowing through the semiconductor light source 110 according to the output signal of the AND gate 190. Here, the second FET 133 is turned on when the value of the output signal of the AND gate 190 is at high level, and is turned off when it is at low level. The first FET 132 and the second FET 133 are connected in parallel, and the current flowing through the semiconductor light source 110 is equal to the sum of the currents flowing through the first FET 132 and the second FET 133.

  The detection resistor 140 generates a detection voltage by the current flowing through the semiconductor light source 110. The sampling switch 150 samples the detection voltage according to the output signal of the AND gate 190 and outputs it to the detection voltage averaging circuit 160. The detection voltage averaging circuit 160 acquires the average value of the sampled detection voltages and outputs it to the current value comparator 125.

  The light source feedback unit 120 compares the intensity of the output light of the semiconductor light source 110 with the external input light intensity target value, and outputs a current target value such that they match. Specifically, first, the photo sensor 121 receives a part of the output light of the semiconductor light source 110 and outputs a light source intensity voltage according to the intensity thereof. The sampling switch 122 samples the light source intensity voltage of the photo sensor 121 according to the output signal of the AND gate 190 and outputs it to the light source intensity averaging circuit 123. The light source intensity averaging circuit 123 acquires an average value of the sampled light source intensity voltage and outputs it to the light source intensity comparator 124. Based on the average value of the input light source intensity voltage and the light intensity target value input from the outside, the light source intensity comparator 124 outputs a target value indicating a current at which they match, to the current value comparator 125. Output to.

  The current value comparator 125 controls the switching power supply 100 by comparing the current value indicated by the average value of the detected voltage with the target current value indicated by the target current value signal and outputting a comparison result signal according to the difference. To do.

  The PWM modulator 170 generates and outputs a PWM modulation signal whose duty cycle value is equal to the PWM setting value of the external input. The rising control circuit 180 generates and outputs a stationary period signal and a rising control signal as follows based on the power supply ON / OFF signal input from the outside and the PWM modulation signal. That is, the rising control circuit 180 outputs to the AND gate 190 a steady period signal which is turned on only in a steady period described later and is turned off in other periods. In addition, the rising control circuit 180 generates a rising control signal having a waveform that is at a low level except for a rising period Tasc described later and that gradually rises in the rising period, and outputs the rising control signal to the first FET 132 via the operational amplifier 131. .. The steady period and the rising period Tasc will be described in detail in Section 1-2.

  The AND gate 190 outputs a logical product of the PWM modulation signal from the PWM modulator 170 and the steady period signal from the rising control circuit 180, and controls ON / OFF of the sampling switch 150, the sampling switch 122, and the second FET 133.

[1-2. motion]
The operation of the semiconductor light source driving device 10 configured as described above will be described below.

  Generally, a semiconductor light source driving device used for a projector or the like that displays an image by PWM-modulating the output light of a semiconductor light source may have a quiescent period for the purpose of periodically preventing a hinge memory. Since the idle period is longer than the PWM modulation cycle, and no current is passed through the semiconductor light source during the idle period, the semiconductor light source does not output light. The semiconductor light source emits PWM-modulated light only in a period excluding the rest period.

  Further, the semiconductor light source gradually heats up during the period of light emission, and radiates heat and cools while it does not emit light. The light output intensity of the semiconductor light source changes with temperature, and even when the same current flows, the semiconductor light source outputs stronger light as the temperature of the semiconductor light source is lower. For example, a semiconductor light source having a temperature of 0 degrees may emit light with an intensity that is three times or more higher than that of a semiconductor light source having a temperature of 100 degrees.

  Therefore, the semiconductor light source after the quiescent period in which light is not output is cooled to a temperature lower than that in the period in which the on / off is switched at high speed for PWM modulation, and becomes a state of emitting stronger light for the same current. ing. If the same current is applied to the semiconductor light source at this time as it was immediately before entering the rest period, the semiconductor light source emits light stronger than immediately before entering the rest period. This is not desirable because if the intensity of light emitted from the semiconductor light source exceeds a certain intensity, it may be damaged due to overheating and melting.

  In the present disclosure, a period immediately after each pause period Toff and having a predetermined second time width is referred to as a rising period Tasc. The second time width is set to a value such as less than 1% of the whole, for example. Further, a period that is neither the rest period Toff nor the rising period Tasc in the entire operation period is called a steady period.

  FIG. 2 is a timing chart showing waveforms of drive control signals and the like in each part of the semiconductor light source drive device 10 according to the first embodiment. In FIG. 2, a period from time t1 to t2 indicates a rest period Toff, and a period from time t2 to t3 indicates a rising period Tasc. Further, the period from time t3 to the start point of the pause period Toff of the next frame is the steady period. The time width of the pause period Toff is longer than the period Tpw of the PWM modulation signal.

  In FIG. 1, the switching power supply 100 is controlled by the comparison result signal input from the current value comparator 125, and supplies power to the semiconductor light source 110 so that the current flowing through the semiconductor light source 110 matches the target current value. The semiconductor light source 110 emits light when a current is supplied from the switching power supply 100, and outputs light to the outside.

  The first FET 132 analog-controls the current flowing through the semiconductor light source 110 according to the rising control signal amplified by the operational amplifier 131. Here, the larger the value of the rising control signal, the larger the current flowing through the semiconductor light source 110, and when the value of the rising control signal is at the high level, the first FET 132 conducts all the current. On the other hand, the smaller the value of the rising control signal is, the smaller the current flowing through the semiconductor light source 110 is. When the value of the rising control signal is low level, the first FET 132 does not flow the current. The second FET 133 controls on / off of the current flowing through the semiconductor light source 110 according to the output signal of the AND gate 190. Here, the second FET 133 is turned on when the value of the output signal of the AND gate 190 is at high level, and is turned off when it is at low level. The first FET 132 and the second FET 133 are connected in parallel, and the current flowing through the semiconductor light source 110 is equal to the sum of the currents flowing through the first FET 132 and the second FET 133.

  The detection resistor 140 generates a detection voltage by the current flowing through the semiconductor light source 110. The sampling switch 150 samples the detection voltage according to the output signal of the AND gate 190 and outputs it to the detection voltage averaging circuit 160. The detection voltage averaging circuit 160 acquires the average value of the sampled detection voltages and outputs it to the current value comparator 125.

  The light source feedback unit 120 compares the intensity of the output light of the semiconductor light source 110 with the external input light intensity target value, and outputs a current target value such that they match. Specifically, first, the photo sensor 121 receives a part of the output light of the semiconductor light source 110 and outputs a light source intensity voltage according to the intensity thereof. The sampling switch 122 samples the light source intensity voltage of the photo sensor 121 according to the output signal of the AND gate 190 and outputs it to the light source intensity averaging circuit 123. The light source intensity averaging circuit 123 acquires an average value of the sampled light source intensity voltage and outputs it to the light source intensity comparator 124. Based on the average value of the input light source intensity voltage and the light intensity target value input from the outside, the light source intensity comparator 124 outputs a target value indicating a current at which they match, to the current value comparator 125. Output to.

  The current value comparator 125 controls the switching power supply 100 by comparing the current value indicated by the average value of the detected voltage with the target current value indicated by the target current value signal and outputting a comparison result signal according to the difference. To do.

  The PWM modulator 170 generates and outputs a PWM modulation signal whose duty cycle value is equal to the PWM setting value of the external input. The rising control circuit 180 generates and outputs a stationary period signal and a rising control signal as follows based on the power supply ON / OFF signal input from the outside and the PWM modulation signal. That is, the rising control circuit 180 outputs to the AND gate 190 a steady period signal that is high level only in the steady period and low level in the other periods. Further, the rising control circuit 180 generates a rising control signal having a waveform that is low level except the rising period and gradually rises to the high level in the rising period, and outputs it to the first FET 132 via the operational amplifier 131.

  The AND gate 190 outputs a logical product of the PWM modulation signal from the PWM modulator 170 and the steady period signal from the rising control circuit 180, and controls ON / OFF of the sampling switch 150, the sampling switch 122, and the second FET 133. Therefore, the current flowing through the semiconductor light source 110 in the steady period is turned on / off according to the PWM modulation signal. The sampling switches 122 and 150 are also controlled by the output signal of the AND gate 190. Therefore, the sampling switches 122 and 150 in the steady period sample the light source intensity voltage and the detection voltage in the period in which the current flows through the semiconductor light source 110. However, the current that actually flows in the semiconductor light source 110 does not rise steeply due to the response characteristics of the second FET 133, the inductance of the switching power supply 100, and the like, and rises with a predetermined time constant, so its waveform is perfect. It does not become a square wave.

  Here, the current flowing through the semiconductor light source 110 is equal to the sum of the currents flowing through the first FET 132 and the second FET 133. However, as described above, the rising control signal is low level except the rising period Tasc, and the output signal of the AND gate 190 is off except the steady period. Therefore, the first FET 132 and the second FET 133 do not flow current at the same time. Therefore, the current flowing through the semiconductor light source 110 is equal to the current flowing through the FET 132 during the steady period and equal to the current flowing through the FET 133 during the rising period Tasc. The current flowing through the semiconductor light source 110 has a waveform as shown in FIG. However, in FIG. 2, Imax is the target current value of the current passed through the semiconductor light source 110.

  Immediately after the end of the rest period Toff, the current flowing through the semiconductor light source 110 gradually increases during the rising period Tasc. Therefore, the semiconductor light source 110 is gradually heated during the rising period Tasc without being suddenly supplied with a current at the start of the rising period Tasc. As a result, it is possible to prevent the semiconductor light source 110 from emitting excessive light due to a sudden current flowing through the semiconductor light source 110 having a low temperature.

  Hereinafter, the loss (power consumption) in the first FET 132 and the second FET 133 will be described. In general, the FET has a very small loss during the period in which no current flows. On the contrary, since the load of the FET is a small value even during the period when the current is passed as it is, the loss of the FET is a small value. The loss is large when the FET is analog-controlled.

  The first FET 132 and the second FET 133 used in the semiconductor light source driving device 10 also have this property. In the steady period, the first FET 132 does not pass a current, and the second FET 133 is controlled so as to switch between the ON period and the OFF period at high speed. Therefore, the loss value is small in any case. Since the first FET 132 and the second FET 133 are both controlled to be off in the idle period Toff, the value of loss becomes minute.

  Since the second FET 133 is off in the rising period Tasc, the loss is very small. The first FET 132 in the rising period Tasc is analog-controlled so that the value of the flowing current gradually increases, and a loss occurs. However, the rising period Tasc is less than 1% of the entire period as described above, and the loss is a negligible minute value as a whole. As described above, the loss in the first FET 132 and the second FET 133 of the semiconductor light source driving device 10 can be suppressed to a very small value as a whole.

[1-3. Effect, etc.]
As described above, the semiconductor light source driving device 10 according to the present embodiment includes the rising control circuit 180. Further, the value of the current flowing through the semiconductor light source 110 in the rising period Tasc immediately after the rest period Toff is controlled so as to gradually increase over the rising period Tasc and reach the maximum at the end of the rising period Tasc. As a result, the temperature of the semiconductor light source 110 gradually rises immediately after the pause period Toff, and thus the semiconductor light source 110 is prevented from emitting excessive light. Further, the loss in the first FET 132 and the second FET 133 is suppressed to a minute value.

(Embodiment 2)
The second embodiment will be described below with reference to FIGS.

[2-1. Constitution]
FIG. 3 is a block diagram showing a configuration example of the semiconductor light source driving device 10A according to the second embodiment. Compared to the semiconductor light source driving device 10 of the first embodiment, the semiconductor light source driving device 10A of FIG. 3 includes a rising control circuit 180A instead of the rising control circuit 180, and a current switching unit 130A instead of the current switching unit 130. Equipped with. The current switching unit 130A includes an OR gate 134 and a third FET 135.

[2-2. motion]
The operation of the semiconductor light source driving device configured as described above will be described below. FIG. 4 is a timing chart showing waveforms of drive control signals and the like in each part of the semiconductor light source drive device 10A of FIG. In FIG. 4, the waveform of the rising control signal is different from that of FIG. 2 and is a train of rising pulse waves whose time width gradually increases.

  The OR gate 134 takes the logical sum of the rising control signal and the output signal of the AND gate 190 and outputs it. As in FIG. 2, the rising control signal and the output signal of the AND gate 190 are not turned on at the same time. Although the output signal of the AND gate 190 is not shown, it has the same waveform as in FIG. Further, the current actually flowing through the semiconductor light source 110 rises with a predetermined time constant as in FIG. 2, and does not become a perfect rectangular wave.

  Therefore, when the pulse width of the first rising pulse wave in the rising control signal of FIG. 4 is sufficiently small, the current flowing through the semiconductor light source 110 is controlled to be off before reaching the maximum value, and the peak amplitude has the target current value Imax. Will be lower than. The pulse width of the next pulse wave is larger than that of the first pulse wave. Therefore, the peak amplitude of the current flowing through the semiconductor light source 110 by the next pulse is larger than the amplitude of the current flowing by the first rising pulse wave.

  As described above, in the rising period Tasc, the rising control circuit 180A outputs a rising control signal which is a train of pulse waves that is intermittently turned on while gradually widening the time width, and controls the FET 135. Since the current flowing through the semiconductor light source 110 gradually increases during the rising period Tasc, the semiconductor light source 110 is gradually heated during the rising period Tasc. Accordingly, it is possible to prevent the semiconductor light source 110 from excessively emitting light due to a current flowing through the semiconductor light source 110 having a temperature lower than that in the steady period immediately after the rest period Toff.

[2-3. Effect, etc.]
As described above, in the semiconductor light source driving device 10A of the present embodiment, the rising control circuit 180 of the semiconductor light source driving device 10 of FIG. 1 is replaced with the rising control circuit 180A, and the current switching unit 130 is replaced with the current switching unit 130A. Thereby, the same effect as that of the semiconductor light source driving device 10 in the first embodiment is obtained.

(Embodiment 3)
The third embodiment will be described below with reference to FIG.

[3-1. Constitution]
FIG. 5 is a block diagram showing a configuration example of the semiconductor light source driving device 10B according to the third embodiment. In FIG. 5, a semiconductor light source driving device 10B is obtained by replacing the light source feedback unit 120 of the semiconductor light source driving device 10 of the first embodiment with a light source feedback unit 120A. The light source feedback unit 120A includes a temperature sensor 126, a current value conversion circuit 127, and a limiter 128. Further, the semiconductor light source driving device 10B inputs a target current value instead of the light intensity target value from an external circuit.

  The current value conversion circuit 127 includes a memory 127m, and the memory 127m stores a limiting current value table. In the limit current value table, the temperature of the semiconductor light source 110 and the maximum current value (limit current value) that can flow without damaging the semiconductor light source 110 at that temperature are stored in advance in association with each other.

[3-2. motion]
The operation of the semiconductor light source driving device 10B of FIG. 5 configured as described above will be described below. In FIG. 5, the temperature sensor 126 measures the junction temperature of the semiconductor light source 110 and outputs the temperature information to the current value conversion circuit 127. The current value conversion circuit 127 refers to the limit current value table of the memory 127m based on the temperature information input from the temperature sensor 126, acquires the limit current value, and outputs it to the limiter 128.

  The method by which the current value conversion circuit 127 acquires the limiting current value is not limited to this. For example, the current value conversion circuit 127 may store a predetermined calculation formula indicating the relationship between the temperature information and the limit current value, and obtain the limit current value by performing calculation using the input temperature information.

  The limiter 128 outputs the smaller value of the limit current value input from the current value conversion circuit 127 and the externally input target current value. Thereby, the semiconductor light source driving device 10B can control the semiconductor light source 110 at a limit level at which the semiconductor light source 110 does not emit excessively even if the input target current value is a value that causes the semiconductor light source 110 to emit excessive light.

[3-3. Effect, etc.]
As described above, the semiconductor light source driving device 10B of the present embodiment replaces the light source feedback unit 120 of the semiconductor light source driving device 10 of FIG. 1 with the light source feedback unit 120A. Thereby, the same effect as that of the semiconductor light source driving device 10 in the first embodiment is obtained.

(Embodiment 4)
FIG. 6 is a block diagram showing a configuration example of the semiconductor light source driving device 10C according to the fourth embodiment. 6, the semiconductor light source driving device 10C is different from the semiconductor light source driving device 10 of FIG. 1 in the following points.
(1) The rising control circuit 180 in FIG. 1 is replaced with the rising control circuit 180A in FIG.
(2) Replace the current switching unit 130 in FIG. 1 with the current switching unit 130A in FIG.
(3) The light source feedback unit 120 in FIG. 1 is replaced with the light source feedback unit 120A in FIG.

  Note that the configuration and operation of each can be referred to the corresponding embodiments described above, and will not be repeated here. As described above, by combining the features of the second and third embodiments to form a new embodiment, the effects of the second and third embodiments can be obtained in combination.

(Other embodiments)
As described above, the first to fourth embodiments have been described as examples of the technique disclosed in the present application. However, the technique of the present disclosure is not limited to these, and can be applied to the embodiment in which appropriate changes, replacements, additions, omissions, and the like are performed. Further, it is also possible to combine the constituent elements described in the above-described first to fourth embodiments to form a new embodiment. Therefore, other embodiments will be exemplified below.

  In the first and second embodiments, the sampling switch 122 and the light source intensity averaging circuit 123 are used as means for obtaining the average value of the optical output of the semiconductor light source 110 during the period when current is flowing in the semiconductor light source 110. Further, in the first to fourth embodiments, the sampling switch 150 and the detection voltage averaging circuit 160 are similarly used as means for obtaining the average value of the current flowing through the semiconductor light source 110 during the period when the current is flowing through the semiconductor light source 110. I was there.

  However, these may be any as long as feedback with sampling is possible. For example, a holding circuit may be used instead of the light source intensity averaging circuit 123 and the detection voltage averaging circuit 160. The holding circuit holds the value of the input immediately before the sampling switches 122 and 150 are turned off until the next switch is turned on.

  In the first and second embodiments, the light emission intensity of the semiconductor light source 110 is acquired as the variable of the semiconductor light source 110 used for feedback by the light source feedback unit 120. Further, in the third and fourth embodiments, the temperature of the semiconductor light source 110 is acquired as the variable of the semiconductor light source 110. However, the variables of the semiconductor light source 110 to be acquired are not limited to these, as long as the heat generation or the temperature of the semiconductor light source 110 can be fed back.

  As described above, the embodiments have been described as examples of the technology according to the present disclosure. To that end, the accompanying drawings and detailed description are provided.

  Therefore, among the constituent elements described in the accompanying drawings and the detailed description, not only constituent elements that are essential for solving the problem but also constituent elements that are not essential for solving the problem in order to exemplify the above technology. Elements may also be included. Therefore, it should not be immediately recognized that the non-essential components are essential by the fact that the non-essential components are described in the accompanying drawings and the detailed description.

  Further, since the above-described embodiments are for exemplifying the technique of the present disclosure, various changes, replacements, additions, omissions, etc. can be made within the scope of the claims or the scope of equivalents thereof.

  The present disclosure can be applied to an apparatus that adjusts the optical output intensity of a semiconductor light source by PWM modulation. Specifically, the present disclosure is applicable to a projection-type image display device (projector) that uses a semiconductor light source, a lighting device, and the like.

10, 10A, 10B, 10C Semiconductor light source driving device 100 Switching power supply 110 Semiconductor light source 120, 120A Light source feedback unit 125 Current value comparator 130, 130A Current switching unit 140 Detection resistor 150 Sampling switch 160 Detection voltage averaging circuit 170 PWM modulator 180, 180A rising control circuit 190 AND gate

Claims (8)

Switching power supply,
A semiconductor light source that emits light by passing an electric current,
Based on a variable of the semiconductor light source, a light source feedback unit that outputs a target current value such that the variable matches the target value of the variable,
The semiconductor light source is controlled in a period excluding a periodical rest period having a first time width in which a current does not flow in the semiconductor light source, by controlling the switching power supply so that the current flowing in the semiconductor light source matches the target current value. PWM output light of,
In the semiconductor light source drive device,
Immediately after the rest period, the temperature of the semiconductor light source is gradually increased in a rising period having a predetermined second time width.
Semiconductor light source driving device. The variable of the semiconductor light source includes the emission intensity of the semiconductor light source,
The semiconductor light source drive device according to claim 1. The variables of the semiconductor light source include the temperature of the semiconductor light source,
The semiconductor light source drive device according to claim 1. By controlling the current flowing through the semiconductor light source to gradually rise in the rising period, the temperature of the semiconductor light source is gradually increased over the rising period,
The semiconductor light source drive device according to claim 1. In the rising period, the current flowing through the semiconductor is controlled to be an intermittent train of pulse waves whose time width gradually increases, thereby gradually increasing the temperature of the semiconductor light source during the rising period.
The semiconductor light source drive device according to claim 1. The semiconductor light source driving device further includes
Rising control circuit,
A current switching unit for controlling a current flowing through the semiconductor light source,
A rising control circuit generates a rising control signal and controls the current switching unit to control the current flowing through the semiconductor light source.
The semiconductor light source drive device according to claim 1. The current switching unit,
A first FET that analog-controls the current in the rising period,
A second FET that controls on / off of a current in a stationary period,
The semiconductor light source drive device according to claim 6. The first FET and the second FET are the same FET,
The semiconductor light source drive device according to claim 7.

Images