JP2019054582A - Control circuit, semiconductor light source driving device, and electronic apparatus - Google Patents

Abstract

To further improve the rising waveform of current in a semiconductor light source element, compared to a conventional technique, without degrading the efficiency.SOLUTION: A semiconductor light source driving device 2 includes a switching element SW1 connected in series with a semiconductor light source element 3, a switching element SW2 connected in parallel with the semiconductor light source element 3 and the switching element SW1, and an inductor L1 connected between a power source, and the semiconductor light source element 3 and the switching elements SW1, SW2. A control circuit 23 generates a control signal PWM1 for cyclically turning on/off the switching element SW1. Within the off time period of the switching element SW1 in each cycle, the control circuit 23 turns on the switching element SW2 during a time period that is immediately before the off-to-on transition of the switching element SW1 and that has a time length equal to or shorter than 1/10 of the time length during which the switching element SW1 is off, and generates a control signal PWM2 for turning off the switching element SW2 during the other time period.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a control circuit of a semiconductor light source driving device that drives at least one semiconductor light source element, a semiconductor light source driving device including such a control circuit, and an electronic apparatus including such a semiconductor light source driving device.

  When the semiconductor light source element is driven by the semiconductor light source driving device, it is necessary to pass a current of a minimum current value or more determined for each element. When the current value becomes less than the minimum current value, the semiconductor light source element is turned off.

  It is known that a semiconductor switch element is driven by a PWM (pulse width modulation) signal so as to realize a dimming function of the semiconductor light source element. The switch element may be connected in parallel with the semiconductor light source element or may be connected in series.

JP 2013-110430 A

  When the switch element is connected in parallel with the semiconductor light source element, since the current flows through the switch element even during a period when no current flows through the semiconductor light source element, the constant current power supply always operates, and the entire semiconductor light source drive device Efficiency is reduced. On the other hand, when the switch element is connected in series with the semiconductor light source element, the constant voltage power supply starts flowing at the moment when the switch element is turned on, so the rising waveform of the current is lost and the actual current value is the target current value. It will be lower.

  The present disclosure provides a control circuit for a semiconductor light source driving apparatus that drives a semiconductor light source element so as to improve the rising waveform of the current of the semiconductor light source element as compared with the conventional one without reducing efficiency. In addition, the present disclosure provides a semiconductor light source driving device including such a control circuit and an electronic apparatus including such a semiconductor light source driving device.

According to the control circuit according to one aspect of the present disclosure,
A control circuit for a semiconductor light source driving device for driving at least one semiconductor light source element,
The semiconductor light source driving device includes a first switch element connected in series with the semiconductor light source element, a second switch element connected in parallel with the semiconductor light source element and the first switch element, and the semiconductor A light source element and an inductor connected between the first and second switch elements and a power source;
The control circuit includes:
Generating a first control signal for periodically turning on and off the first switch element;
Of the period in which the first switch element is turned off in each cycle, immediately before the first switch element is changed from off to on, 1 / of the length of time during which the first switch element is turned off. A second control signal is generated to turn on the second switch element in a period of time length of 10 or less and turn off the second switch element in another period.

  According to the control circuit of one embodiment of the present disclosure, as described above, the semiconductor light source element, the first and second switch elements, and the inductor are connected, and the second switch element is operated, thereby improving the efficiency. The rising waveform of the current of the semiconductor light source element can be improved as compared with the conventional one without lowering.

1 is a block diagram showing a configuration of a projector 10 according to a first embodiment. FIG. 2 is a circuit diagram illustrating configurations of a semiconductor light source driving device 2 and a semiconductor light source element 3 in FIG. 3 is a timing chart showing waveforms of signals in the semiconductor light source driving device 2 of FIG. 2. It is a graph which shows the waveform of each signal in the semiconductor light source drive device 2 which concerns on the Example of this embodiment. It is a graph which shows the waveform of each signal in the semiconductor light source drive device concerning the 1st comparative example. It is a graph which shows the waveform of each signal in the semiconductor light source drive device concerning the 2nd comparative example. It is a circuit diagram which shows the structure of 2 A of semiconductor light source drive devices and semiconductor light source element 3-1, 3-2 which concern on 2nd Embodiment.

  Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, more detailed description than necessary may be omitted. For example, detailed descriptions of already well-known matters and repeated descriptions for substantially the same configuration may be omitted. This is to avoid the following description from becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. The inventor (s) provides the accompanying drawings and the following description in order for those skilled in the art to fully understand the present disclosure, and is intended to limit the subject matter described in the claims. Not what you want.

[1. First Embodiment]
The first embodiment will be described with reference to FIGS.

[1-1. Constitution]

  FIG. 1 is a block diagram illustrating a configuration of a projector 10 according to the first embodiment. The projector 10 is an example of an electronic device that receives image data and projects the image data onto the screen 11. The projector 10 includes an image processing device 1, a semiconductor light source driving device 2, a semiconductor light source element 3, a MEMS mirror device 4, and an optical system 5. The image processing device 1 generates control signals for the semiconductor light source driving device 2 and the MEMS mirror device 4 based on the input image data. The semiconductor light source driving device 2 controls the current supplied to the semiconductor light source element 3 in accordance with a control signal from the image processing device 1. The semiconductor light source element 3 is, for example, one or a plurality of light emitting diodes. The light generated by the semiconductor light source element 3 is sent to the MEMS mirror device 4. The MEMS mirror device 4 projects the light sent from the semiconductor light source element 3 onto the screen 7 via the optical system 5 in accordance with a control signal from the image processing device 1.

  FIG. 2 is a circuit diagram showing the configuration of the semiconductor light source driving device 2 and the semiconductor light source element 3 of FIG. The semiconductor light source driving device 2 includes a constant voltage power supply circuit 21, a current detection circuit 22, a control circuit 23, diodes D1 and D2, an inductor L1, a current detection resistor R1, and switch elements SW1 and SW2.

  The semiconductor light source element 3 includes one or a plurality of unit elements. When the semiconductor light source element 3 includes a plurality of unit elements, these unit elements are connected in series and / or in parallel. Each unit element is, for example, a light emitting diode.

  The constant voltage power circuit 21 generates a constant DC input voltage Vin.

  In the present disclosure, the constant voltage power supply circuit 21 is also referred to as “power supply”.

  The switch element SW1 is connected in series with the semiconductor light source element 3. The switch element SW2 is connected in parallel with the semiconductor light source element 3 and the switch element SW1. The switch elements SW1 and SW2 are, for example, field effect transistors. The inductor L1 is connected between the semiconductor light source element 3 and the switch elements SW1 and SW2 and the constant voltage power supply circuit 21. The switch element SW2 and the inductor L1 constitute a booster circuit.

  In the present disclosure, the switch elements SW1 and SW2 are also referred to as “first switch element” and “second switch element”.

  Based on a control signal (dimming signal) from the image processing apparatus 1, the control circuit 23 periodically turns on and off the switch element SW1 and periodically turns on and off the switch element SW2. A second control signal PWM2 that is turned off is generated. The control circuit 23 turns on the switch element SW2 in a very short period immediately before switching the switch element SW1 from off to on among the periods in which the switch element SW1 is turned off in each cycle, and the switch element SW1 in other periods. A control signal PWM2 is generated so as to turn off SW2. For example, the control circuit 23 generates the control signal PWM2 so as to turn on the switch element SW2 in a period of 1/10 or less of the time length in which the switch element SW1 is turned off. For example, the control circuit 23 may generate the control signal PWM2 so as to turn on the switch element SW2 in a period longer than 1/20 and 1/10 or less of the time length during which the switch element SW1 is turned off. .

  The control signals PWM1 and PWM2 are, for example, PWM signals. The control signal PWM1 is generated so as to control (dimming) the brightness of the projected image, for example.

  The diode D1 is connected between the semiconductor light source element 3 and the switch element SW1 and the inductor L1. The diode D2 is connected in parallel with the inductor L1 and the diode D1. The switch element SW2 is connected to a node between the inductor L1 and the diode D1. The diode D1 is used to prevent current backflow. The diode D2 is used as a bypass diode for preventing the switch element SW2 from being destroyed by a surge voltage generated from the inductor L1 when the switch element SW1 is turned on.

  In the present disclosure, the diodes D1 and D2 are also referred to as “first diode” and “second diode”.

  The current detection resistor R <b> 1 is connected between the semiconductor light source element 3 and the switch elements SW <b> 1 and SW <b> 2 and the constant voltage power supply circuit 21. The current detection circuit 22 detects the current flowing through the semiconductor light source element 3 based on the voltage applied to both ends of the current detection resistor R1. The control circuit 23 generates the control signals PWM1 and PWM2 so as to keep the peak value of the current flowing through the semiconductor light source element 3 constant. The control circuit 23 compares the dimming signal with the voltage value of the current detection resistor R1, turns on and off the switch element SW1 according to the calculated duty ratio, and performs PWM dimming.

  The output voltage Vout and the output current Iout of the semiconductor light source driving device 2 are supplied to the semiconductor light source element 3.

  As described above, the semiconductor light source driving device 2 has a booster circuit that operates only when necessary (ie, the switch element SW2) in the circuit that drives the semiconductor light source element 3 by the switch element SW1 connected in series with the semiconductor light source element 3. And an inductor L1).

[1-2. Operation]
FIG. 3 is a timing chart showing waveforms of signals in the semiconductor light source driving device 2 of FIG. The control signal PWM1 has a period T1 in which the switch element SW1 is turned off and a period T2 in which the switch element SW1 is turned on in each cycle (represented by a period T0). The control signal PWM2 has a time length equal to or less than 1/10 of the time length of the period T1 immediately before the switch element SW1 is changed from OFF to ON in the period T1 in which the switch element SW1 is OFF in each cycle. It has a period T3. In the period T3 of the control signal PWM2, the switch element SW2 is turned on, and in other periods other than the period T3 of the control signal PWM2, the switch element SW2 is turned off. Accordingly, the switch element SW2 is always turned off immediately before the switch element SW1 is turned on. In the period T3, energy is stored in the inductor L1, so that the output voltage Vout is boosted. By operating the switch element SW2 in this way, the rising waveform of the current of the semiconductor light source element 3 can be improved as compared with the conventional one without reducing the efficiency.

  According to FIG. 3, a constant input voltage Vin is generated by the constant voltage power supply circuit 21, and is constant from the constant voltage power supply circuit 21 to the semiconductor light source element 3 via the inductance L <b> 1 and the diode D <b> 1 during most of each period. The voltage V1 is applied. In the period T3 in which the switch element SW2 is on, the output voltage Vout is lower than the voltage V1. When the switch element SW2 transitions from on to off, the output voltage Vout transiently increases beyond the voltage V1. Thereafter, when the switch element SW1 is turned on, the increased output voltage Vout is applied to the semiconductor light source element 3, so that an output current Iout having a steep rise flows to the semiconductor light source element 3.

  FIG. 4 is a graph showing the waveform of each signal in the semiconductor light source driving apparatus 2 according to an example of the present embodiment. The upper part of FIG. 4 shows the waveform of the output current Iout, the middle part shows the waveform of the control signal PWM2, and the lower part shows the waveform of the drain-source voltage Vds of the switch element SW2. The graph of FIG. 4 was measured by actually operating the circuit of FIG. In the measurement, an output current Iout having a current value of 3 A was generated when the switch element SW1 was turned on by performing pulse width modulation with a frequency of 150 kHz and a duty ratio of 50%. In the measurement, the input voltage Vin was 380V. In the measurement, the operating environment was room temperature.

  FIG. 5 is a graph showing waveforms of signals in the semiconductor light source driving device according to the first comparative example. FIG. 5 shows a waveform of an output current (current flowing through the semiconductor light source element 3) in a configuration in which the switch element SW2, the inductor L1, and the diodes D1 and D2 are removed from the semiconductor light source driving apparatus 2 of FIG. Pulse width modulation, input voltage, and operating environment conditions were the same as in FIG.

  4 and FIG. 5, in the comparative example (FIG. 5), the rising waveform at the moment when the switch element SW1 is turned on is broken, whereas in this embodiment (FIG. 4), the rising waveform is broken. It can be reduced as compared with the comparative example, and it can be seen that it is approaching a rectangular wave.

  FIG. 6 is a graph showing waveforms of signals in the semiconductor light source driving apparatus according to the second comparative example. FIG. 6 illustrates a case where the switch element SW2 is turned on in a short period after the switch element SW1 is turned on, not in the period T3 immediately before the switch element SW1 is changed from off to on in the semiconductor light source driving device 2 according to the embodiment. Indicates. Similar to FIG. 4, the upper stage of FIG. 6 shows the waveform of the output current Iout, the middle stage shows the waveform of the control signal PWM2, and the lower stage shows the waveform of the drain-source voltage Vds of the switch element SW2. Pulse width modulation, input voltage, and operating environment conditions were the same as in FIG.

  According to FIG. 6, the overshoot of the output current Iout occurs due to the improper time position of the period in which the switch SW2 is turned on. If an overshoot of the output current Iout occurs, the semiconductor light source element 3 may be deteriorated. On the other hand, according to FIG. 4, when the switch element SW2 is once turned on for the period T3 immediately before the switch element SW1 transitions from off to on, and then turned off, no overshoot occurs.

  By limiting the time length of the period T3 during which the switch element SW2 is turned on to a very short period immediately before the switch element SW1 is turned on, loss due to boosting can be reduced. This loss hardly affects the overall efficiency of the semiconductor light source driving device 2.

  The control circuit 23 may set the length of the period T3 to a fixed value, and compensates for the waveform distortion as shown in FIG. 5 so that the waveform of the output current Iout approaches the rectangular wave. May be determined.

[1-3. Effect]
The control circuit, the semiconductor light source driving device, and the electronic device according to the first embodiment have the following configurations.

  The control circuit 23 according to the first embodiment is the control circuit 23 of the semiconductor light source driving device 2 that drives at least one semiconductor light source element 3. The semiconductor light source driving device 2 includes a switch element SW1 connected in series with the semiconductor light source element 3, a switch element SW2 connected in parallel with the semiconductor light source element 3 and the switch element SW1, a semiconductor light source element 3 and a switch element SW1, An inductor L1 connected between SW2 and the constant voltage power supply circuit 21 is provided. The control circuit 23 generates a first control signal PWM1 that periodically turns on and off the switch element SW1. In the period T1 in which the switch element SW1 is turned off in each cycle, the control circuit 23 is 1/10 or less of the time length in which the switch element SW1 is turned off immediately before the switch element SW1 is changed from off to on. A second control signal PWM2 is generated that turns on the switch element SW2 in the time period T3 and turns off the switch element SW2 in the other period.

  The control circuit 23 according to the first embodiment is configured to turn on the switch element SW2 in a period T3 having a time length of 1/20 or more and 1/10 or less of the time length of turning off the switch element SW1. The control signal PWM2 may be generated.

  According to the control circuit 23 according to the first embodiment, the first control signal PWM1 and the second control signal PWM2 may be PWM signals.

  The semiconductor light source driving device 2 according to the first embodiment is a semiconductor light source driving device 2 that drives at least one semiconductor light source element 3. The semiconductor light source driving device 2 includes a switch element SW1 connected in series with the semiconductor light source element 3, a switch element SW2 connected in parallel with the semiconductor light source element 3 and the switch element SW1, a semiconductor light source element 3 and a switch element SW1, An inductor L1 connected between SW2 and the constant voltage power supply circuit 21 and a control circuit 23 are provided.

  The semiconductor light source driving apparatus 2 according to the first embodiment includes a diode D1 connected between the semiconductor light source element 3 and the switch element SW1, and the inductor L1, and a diode D2 connected in parallel with the inductor L1 and the diode D1. And may further be provided. The switch element SW2 is connected to a node between the inductor L1 and the diode D1.

  The semiconductor light source drive device 2 according to the first embodiment includes a current detection resistor R1 connected between the semiconductor light source element 3 and the switch elements SW1 and SW2 and the constant voltage power supply circuit 21, and both ends of the current detection resistor R1. You may further provide the current detection circuit 22 which detects the electric current which flows into the semiconductor light source element 3 based on this voltage. The control circuit 23 generates the first control signal PWM1 and the second control signal PWM2 so as to keep the peak value of the current flowing through the semiconductor light source element 3 constant.

  According to the semiconductor light source driving device 2 according to the first embodiment, the switch elements SW1 and SW2 may be field effect transistors.

  The electronic apparatus according to the first embodiment includes at least one semiconductor light source element 3 and a semiconductor light source driving device 2.

  According to the first embodiment, as described above, the semiconductor light source device 3, the switch devices SW1 and SW2, and the inductor L1 are connected to operate the switch device SW2, thereby reducing the efficiency of the semiconductor light source. The rising waveform of the current of the element 3 can be improved as compared with the prior art.

  According to the first embodiment, when the current of the semiconductor light source element 3 is dimmed, the rising waveform of the current of the semiconductor light source element 3 can be improved without reducing efficiency by adding a small amount of components. Can do.

  According to the first embodiment, improvement of flicker and the like when lighting at low luminance can be expected.

[2. Second Embodiment]
The second embodiment will be described with reference to FIG.

  In the first embodiment, the case where one semiconductor light source element 3 is driven has been described. However, the semiconductor light source driving device according to the embodiment of the present disclosure may drive a plurality of semiconductor light source elements 3. In the second embodiment, such a case will be described.

  FIG. 7 is a circuit diagram showing a configuration of the semiconductor light source driving device 2A and the semiconductor light source elements 3-1 and 3-2 according to the second embodiment. The semiconductor light source driving device 2A is configured similarly to the semiconductor light source driving device 2 of FIG. In the semiconductor light source driving device 2A, the first semiconductor light source element 3-1 is connected between the switch element SW1 and one terminal of the constant voltage power supply circuit 21, and the other terminal of the switch element SW1 and constant voltage power supply circuit 21 is connected. The second semiconductor light source element 3-2 is connected between the two. Each of the semiconductor light source elements 3-1 and 3-2 includes one or a plurality of unit elements, like the semiconductor light source element 3 of FIG.

  According to the second embodiment, the degree of freedom in designing the electronic device can be improved as compared with the case of the first embodiment.

[Other Embodiments]
As described above, each embodiment has been described as an example of the technique disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can also be applied to embodiments in which changes, replacements, additions, omissions, and the like have been made as appropriate. Moreover, it is also possible to combine each component demonstrated by the said embodiment into a new embodiment.

  The projector 10 in FIG. 1 is an example of an electronic apparatus according to the present disclosure. However, the electronic apparatus according to the present disclosure may be another image forming apparatus that drives the semiconductor light source element, such as a laser printer.

  As described above, the embodiments have been described as examples of the technology in the present disclosure. For this purpose, the accompanying drawings and detailed description are provided.

  Accordingly, among the components described in the accompanying drawings and the detailed description, not only the components essential for solving the problem, but also the components not essential for solving the problem in order to illustrate the above technique. May also be included. Therefore, it should not be immediately recognized that these non-essential components are essential as those non-essential components are described in the accompanying drawings and detailed description.

  Moreover, since the above-mentioned embodiment is for demonstrating the technique in this indication, a various change, substitution, addition, abbreviation, etc. can be performed in a claim or its equivalent range.

1 ... Image processing device,
2, 2A ... Semiconductor light source driving device,
3,3-1, 3-2 ... semiconductor light source element,
4 ... MEMS mirror device,
5 ... Optical system,
10 ... Projector,
11 ... Screen,
21 ... Constant voltage power supply circuit,
22 ... current detection circuit,
23 ... Control circuit,
D1, D2 ... diodes,
L1 ... inductor,
R1 ... current detection resistor,
SW1, SW2 ... switch elements.

Claims (9)

A control circuit for a semiconductor light source driving device for driving at least one semiconductor light source element,
The semiconductor light source driving device includes a first switch element connected in series with the semiconductor light source element, a second switch element connected in parallel with the semiconductor light source element and the first switch element, and the semiconductor A light source element and an inductor connected between the first and second switch elements and a power source;
The control circuit includes:
Generating a first control signal for periodically turning on and off the first switch element;
Of the period in which the first switch element is turned off in each cycle, immediately before the first switch element is changed from off to on, 1 / of the length of time during which the first switch element is turned off. Generating a second control signal for turning on the second switch element in a period of 10 or less time length and turning off the second switch element in another period;
Control circuit. The control circuit turns on the second switch element so as to turn on the second switch element in a period of 1/20 or more and 1/10 or less of a time length of turning off the first switch element. Generate control signals,
The control circuit according to claim 1. The first and second control signals are PWM signals;
The control circuit according to claim 1 or 2. A semiconductor light source driving apparatus for driving at least one semiconductor light source element,
A first switch element connected in series with the semiconductor light source element;
A second switch element connected in parallel with the semiconductor light source element and the first switch element;
An inductor connected between the semiconductor light source element and the first and second switch elements and a power source;
A control circuit according to claim 1,
Semiconductor light source driving device. A first diode connected between the semiconductor light source element and the first switch element and the inductor;
A second diode connected in parallel with the inductor and the first diode;
The second switch element is connected to a node between the inductor and the first diode;
The semiconductor light source driving device according to claim 4. A current detection resistor connected between the semiconductor light source element and the first and second switch elements and a power source;
A current detection circuit for detecting a current flowing through the semiconductor light source element based on a voltage applied to both ends of the current detection resistor;
The control circuit generates the first and second control signals so as to keep a peak value of a current flowing through the semiconductor light source element constant.
The semiconductor light source driving device according to claim 4 or 5. The first and second switch elements are field effect transistors,
The semiconductor light source drive device according to claim 4. At least one semiconductor light source element;
A semiconductor light source driving device according to claim 4,
Electronics. A first semiconductor light source element connected between the first switch element and a first terminal of the power source;
A second semiconductor light source element connected between the first switch element and a second terminal of the power source;
The electronic device according to claim 8.

Images