JP2020140796A - Light emission control device, light source device and projection type image display device - Google Patents

Abstract

To provide a light emission control device or the like that can appropriately stop an overcurrent even when both ends of a sense resistor for detecting a current flowing through a light emission element are short-circuited.SOLUTION: A light emission control device 100 includes a detection circuit 132 and a light emission control circuit 101. The detection circuit 132 detects the potential difference between both ends of a second resistor RIS. The light emission control circuit 101 outputs a first control signal DRV for controlling ON/OFF of a first switching element 11 and a second control signal GTB for controlling ON/OFF of a second switching element 12. When it is detected that the potential difference between both the ends of the second resistor RIS is larger than a threshold value, the light emission control circuit 101 stops a current flowing through the second switching element 12 and then performs restart processing to increase the current. The light emission control circuit 101 deactivates at least one of the first control signal DRV and the second control signal GTB when the restart processing is performed at a predetermined number of times.SELECTED DRAWING: Figure 1

Description

The present invention relates to a light emission control device, a light source device, a projection type image display device, and the like.

A light emission control device that controls a light source used in a projector or the like is known. The light emission control device controls switching regulation by turning on / off a transistor that allows current to flow through an inductor, and controls the amount of light emitted by the light emitting element by passing a constant current obtained by the switching regulation control to the light emitting element. To do. At this time, the light emission control device detects the current flowing through the light emitting element and the current flowing through the transistor for switching regulation, and performs switching regulation control based on these currents. The prior art of such a light emission control device is disclosed in, for example, Patent Document 1.

Japanese Unexamined Patent Publication No. 2018-106862

The light emission control device performs overcurrent detection in order to avoid an abnormality or failure due to overcurrent. Conventionally, an overcurrent of a light emitting element is detected by connecting a light emitting element and a sense resistor in series and detecting whether or not the potential difference between both ends of the sense resistor is equal to or more than a predetermined value. However, when both ends of the sense resistor are short-circuited, the potential difference between both ends of the sense resistor becomes smaller than the original value. Therefore, even though an overcurrent is flowing through the light emitting element, the overcurrent may not be detected correctly and the overcurrent may continue to flow through the light emitting element.

In one aspect of the present invention, a light emitting element, a first resistor, and a first switching element provided in series between the first power supply node and the first node are connected in series between the first power supply node and the second power supply node. A light emission control device that controls the first switching element and the second switching element of the light source circuit including the inductor, the second switching element, and the second resistor provided in the above, and the potential difference between both ends of the second resistor. The light emission control circuit including a detection circuit for detection, a first control signal for controlling the on / off of the first switching element, and a second control signal for controlling the on / off of the second switching element, and the like. When the detection circuit detects that the potential difference between both ends of the second resistor is larger than the threshold value, the light emission control circuit has a restart process of stopping the current flowing through the second switching element and then increasing the current. The present invention relates to a light emitting control device that performs a stop process for inactivating at least one of the first control signal and the second control signal when the restart process is performed two or more predetermined times.

Configuration example of the light source device. Configuration example of the light source device. Waveform diagram in analog dimming mode. Waveform diagram in PWM dimming mode. The waveform diagram explaining the stop processing. Detailed configuration example of the detection circuit. Detailed configuration example of the operation control circuit. The waveform diagram explaining the operation of the operation control circuit. Detailed configuration example of the soft start control circuit. The waveform diagram explaining the operation of the soft start control circuit. Waveform diagram when soft start processing is performed under normal conditions. Configuration example of a projection type image display device.

Hereinafter, preferred embodiments of the present disclosure will be described in detail. It should be noted that the present embodiment described below does not unreasonably limit the contents described in the claims, and not all of the configurations described in the present embodiment are essential constituent requirements.

1. 1. Light source device, light emission control device FIGS. 1 and 2 are configuration examples of the light source device 200. The light source device 200 includes a light source circuit 10 which is a light emitting element and its peripheral circuit, and a light emitting control device 100 which controls light emission of the light emitting element. The light emission control device 100 is, for example, an integrated circuit device, and is realized by, for example, a semiconductor chip.

First, the configurations of the light source circuit 10 and the light emission control device 100 will be described with reference to FIGS. 1 and 2, and the PWM dimming mode and the analog dimming mode will be described with reference to FIGS. 3 and 4. After that, the overcurrent detection will be described in FIGS.

As shown in FIG. 2, the light source circuit 10 includes a first switching element 11, a second switching element 12, an inductor 14, and a light emitting element 15. Further, the light source circuit 10 includes a first resistor RCS, a second resistor RIS, a capacitor CA, and a diode DA. Note that FIG. 1 illustrates a case where the first switching element 11 and the second switching element 12 are N-type transistors, but these switching elements are not limited to N-type transistors.

The light emitting element 15 is driven by the current ILD and emits light with a brightness corresponding to the current value of the current ILD. The light emitting element 15 is a plurality of laser diodes connected in series. However, the light emitting element 15 may be one laser diode or an LED (Light Emitting Diode).

The light emitting element 15 and the first switching element 11 are provided in series between the first power supply node NVI and the first node N1. The first node N1 is a node connected to one end of the inductor 14. The inductor 14, the second switching element 12, and the second resistor RIS are provided in series between the first node N1 and the second power supply node NGN. Specifically, the first resistor RCS is connected between the first power supply node NVI and one end of the light emitting element 15, the other end of the light emitting element 15 is connected to the drain of the first switching element 11, and the first switching element 11 Source is connected to one end of the inductor 14. The other end of the inductor 14 is connected to the drain of the second switching element 12, and the second resistor RIS is connected between the source of the second switching element 12 and the second power supply node NGN. The first power supply node NVI is a node to which the first power supply is input, and the second power supply node NGN is a node to which the second power supply is input. The voltage of the first power supply is higher than the voltage of the second power supply. The second power source is, for example, ground. The connection relationship between the capacitor CA and the diode DA is as shown in FIG. 2, and the operation of the light source circuit 10 including these circuit elements will be described later in FIGS. 3 and 4.

The second switching element 12 controls the switching regulation of the current flowing through the inductor 14. The first switching element 11 controls whether or not the current flowing through the inductor 14 flows through the light emitting element 15. Although the details will be described later, a mode in which the first switching element 11 is always on and the light emitting amount of the light emitting element 15 is controlled by the switching regulate control of the second switching element 12 is called an analog dimming mode. Further, a mode in which the light emitting amount of the light emitting element 15 is controlled by the on-duty of the first switching element 11 by turning it on and off is called a PWM dimming mode.

As shown in FIG. 1, the light emission control device 100 includes a light emission control circuit 101 and a detection circuit 132. Further, the light emission control device 100 includes a PWM terminal TDCS, a dimming voltage input terminal TACS, and terminals TDRV, TGTB, TIS, TCSP, and TCSN.

A PWM signal DCS used for dimming control in the PWM dimming mode is input to the PWM terminal TDCS from the processing device. The dimming voltage ACS used for dimming control in the analog dimming mode is input from the processing device to the dimming voltage input terminal TACS. The processing device is a host device of the light emission control device 100, and is a processor such as an MPU or a CPU.

The light emission control circuit 101 controls the on / off control of the first switching element and the second switching element based on the PWM signal DCS and the dimming voltage ACS to control the light emission amount of the light emitting element 15. The light emission control circuit 101 includes a first drive circuit 110, a second drive circuit 120, an oscillation circuit 140, a soft start control circuit 135, and an operation control circuit 133.

The first drive circuit 110 outputs a first control signal DRV that controls the first switching element 11 on or off based on the PWM signal DCS. The first control signal DRV is output from the terminal TDRV and input to the gate of the first switching element 11. The first drive circuit 110 outputs a first control signal DRV that turns on the first switching element 11 when the PWM signal DCS is active, and turns off the first switching element 11 when the PWM signal DCS is inactive. 1 Outputs the control signal DRV. The first drive circuit 110 is composed of, for example, a buffer circuit that buffers the PWM signal DCS.

The oscillation circuit 140 generates the clock signal CLK. For example, the oscillation circuit 140 is a CR oscillation circuit, a ring oscillator, a multivibrator, or the like.

The second drive circuit 120 outputs the second control signal GTB based on the dimming voltage ACS, the PWM signal DCS, and the clock signal CLK. The second control signal GTB is output from the terminal TGTB and input to the gate of the second switching element 12. The second control signal GTB controls the on / off of the second switching element 12 during the period in which the PWM signal DCS is active. Specifically, the voltage CSP at one end of the first resistor RCS is input to the terminal TCSP, the voltage CSN at the other end of the first resistor RCS is input to the terminal TCSN, and the voltage IS at one end of the second resistor RIS is the terminal TIS. Is entered in. The second drive circuit 120 switches and regulates the current ILD flowing through the light emitting element 15 based on the voltage CSP, CSN, IS and the dimming voltage ACS to obtain the current ILD corresponding to the dimming voltage ACS. Control to be.

The second drive circuit 120 includes a control signal output circuit 121, a slope compensation circuit 122, a current detection circuit 123, an error amplifier circuit 124, a switch circuit 125, and a comparator 126. Hereinafter, the operation of each part of the second drive circuit 120 and the operation of the first drive circuit 110 in each dimming mode will be described with reference to the waveform diagrams of FIGS. 3 and 4. In the following, active is set to high level and inactive is set to low level.

FIG. 3 is a waveform diagram in the analog dimming mode. In the analog dimming mode, the PWM signal DCS is at a high level. The first drive circuit 110 outputs a high-level first control signal DRV to always turn on the first switching element 11. In the PWM dimming mode, the PWM signal DCS is a rectangular wave having a high-width duty of less than 100%. Therefore, the always high level PWM signal DCS in the analog dimming mode is set as a PWM signal having a high width duty of 100%.

The current detection circuit 123 outputs the detection voltage DTQ by multiplying the potential difference CSP-CSN = RCS × ILD at both ends of the first resistor RCS by a given gain. The error amplifier circuit 124 amplifies the error between the detection voltage DTQ and the dimming voltage ACS. The switch circuit 125 is on when the PWM signal DCS is at a high level and is off when the PWM signal DCS is at a low level. In the analog dimming mode, the switch circuit 125 is always on.

The slope compensation circuit 122 increases the slope of the voltage IS with time change and outputs the voltage SLQ after the slope increase in order to suppress the subharmonic oscillation of the drive current flowing through the laser diode. The comparator 126 compares the voltage SLQ with the output voltage ERQ of the error amplifier circuit 124, outputs a low-level signal CPQ when SLQ <ERQ, and outputs a high-level signal CPQ when SLQ> ERQ.

The control signal output circuit 121 shifts the second control signal GTB from the low level to the high level at the edge of the clock signal CLK. Since the second switching element 12 is on when the second control signal GTB is at a high level, a current flows from the inductor 14 to the second power supply node NGN via the second switching element 12 and the second resistor RIS. Since the current flowing through the inductor 14 increases, the voltage IS rises and the output voltage SLQ of the slope compensation circuit 122 rises. Since the current flowing through the inductor 14 flows through the light emitting element 15 via the first switching element 11, the current ILD flowing through the light emitting element 15 also increases.

When SLQ> ERQ, the output signal CPQ of the comparator 126 transitions from low level to high level. At this time, the control signal output circuit 121 shifts the second control signal GTB from the high level to the low level. When the second control signal GTB is at a low level, since the second switching element 12 is off, a current flows from the inductor 14 to the first power supply node NVI via the diode DA. Since the current flowing through the inductor 14 is reduced, the current ILD flowing through the light emitting element 15 is also reduced.

When the detection voltage DTQ, which is the detection result of the current ILD, and the dimming voltage ACS are different, the output voltage ERQ of the error amplifier circuit 124 changes, so that the duty of the second control signal GTB changes. As a result, the current ILD is feedback-controlled so that the detected voltage DTQ matches the dimming voltage ACS. By such feedback control, the current ILD is kept constant. The control that keeps this current ILD constant is called switching regulate control. The current ILD is maintained at a current value corresponding to the dimming voltage ACS, and when the processing device changes the dimming voltage ACS, the current ILD changes accordingly. That is, in the analog dimming mode, the amount of light emitted from the light emitting element 15 is dimmed by the dimming voltage ACS.

The above analog dimming mode is used from the maximum value of the current ILD to a predetermined value. That is, the analog dimming mode is used when the light emitting element 15 emits light with high brightness. On the other hand, when the current ILD is less than a predetermined value, that is, when the light emitting element 15 emits light with low brightness, the PWM dimming mode is used.

FIG. 4 is a waveform diagram in the PWM dimming mode. The period of the PWM signal DCS is TPWM, and the period of high level of the PWM signal DCS is THW. The duty of the PWM signal DCS is (THW / TPWM) × 100%. The frequency of the second control signal GTB is set higher than the frequency of the PWM signal DCS.

When the PWM signal DCS is at a high level, the first drive circuit 110 outputs a high-level first control signal DRV and turns on the first switching element 11. At this time, the second drive circuit 120 switches the second control signal GTB to perform switching regulation control. As a result, the current ILD corresponding to the dimming voltage ACS flows through the light emitting element 15. When the PWM signal DCS is low level, the first drive circuit 110 outputs a low level first control signal DRV and turns off the first switching element 11. Further, the second drive circuit 120 lowers the second control signal GTB to a low level. At this time, no current flows through the light emitting element 15.

Since the time average of the current ILD flowing through the light emitting element 15 is determined by the duty of the PWM signal DCS, the amount of light emitted is also determined by the duty of the PWM signal DCS. As described above, in the PWM dimming mode, dimming is controlled by the duty of the PWM signal DCS. On the other hand, the current value when the current ILD is flowing through the light emitting element 15 is secured to be higher than the time average. In order to make the laser diode emit light, it is necessary to pass a current ILD equal to or higher than the threshold value through the laser diode. By performing the PWM control as described above, it is possible to make the laser diode emit light by passing a current ILD equal to or higher than the threshold value, and to perform dimming as a time average.

2. 2. Overcurrent detection Next, overcurrent detection will be described. First, a comparative example will be described, and then the overcurrent detection of the present embodiment will be described.

In the comparative example, it is determined whether or not an overcurrent has flowed through the light emitting element 15 based on the potential difference (CSP-CSN) at both ends of the first resistor RCS. When it is determined that an overcurrent has flowed through the light emitting element 15, the second drive circuit 120 turns off the second switching element 12 by deactivating the second control signal GTB. As a result, the current path is cut off, so that no current flows through the light emitting element 15.

Further, in the comparative example, it is determined whether or not an overcurrent has flowed through the second switching element 12 based on the voltage IS at one end of the second resistor RIS. When it is determined that an overcurrent has flowed through the second switching element 12, the second drive circuit 120 restarts the switching regulation control. At the restart, a soft start is performed in which the on-duty of the second switching element 12 is gradually increased. This suppresses overcurrent. As will be described later, a large current may flow through the second switching element 12 even in the normal state. Therefore, even if the overcurrent of the second switching element 12 is detected, the switching regulation control is not stopped but restarted.

In the above comparative example, whether or not an overcurrent has flowed through the light emitting element 15 is determined based on the potential difference between both ends of the first resistor RCS. Therefore, if both ends of the first resistor RCS are short-circuited, it may not be possible to appropriately deal with the overcurrent. That is, when both ends of the first resistor RCS are short-circuited, a current flows through the path due to the short circuit, so that the potential difference between both ends of the first resistor RCS becomes small. Therefore, the current detection circuit 123 erroneously determines that the current flowing through the light emitting element 15 is small, and the second drive circuit 120 increases the current flowing through the light emitting element 15. That is, even if a large current actually flows through the light emitting element 15, the current of the light emitting element 15 may be further increased, and the current or the amount of light emitted may exceed the rating.

In the present embodiment, overcurrent can be appropriately dealt with by determining whether or not both ends of the first resistor RCS are short-circuited based on the potential difference between both ends of the second resistor RIS.

A short circuit is the occurrence of an abnormal current path other than the regular current path. That is, a short circuit at both ends of a resistor means that an abnormal current path connecting both ends of the resistor is generated due to adhesion of metal or dust, or improper mounting. Since a current path is generated in parallel with the resistor due to the short circuit, the resistance value is apparently lowered. This apparent resistance value is not limited to zero Ω, and if the apparent resistance value is larger than zero Ω, it is included in the short circuit.

Hereinafter, the present embodiment will be described in detail. First, the overcurrent detection performed by the light emission control device 100 will be described with reference to FIGS. 1 and 2. Hereinafter, the potential difference between both ends of the first resistance RCS is referred to as a first potential difference, and the potential difference between both ends of the second resistance RIS is referred to as a second potential difference.

The detection circuit 132 detects the second potential difference, which is the potential difference between both ends of the second resistance RIS, by detecting the voltage IS at one end of the second resistance RIS. Specifically, the detection circuit 132 detects whether or not the second potential difference is smaller than the threshold value, and outputs the detection signal DETB as a result. The threshold value is a threshold value for detecting the overcurrent of the second switching element 12. It is set to a value sufficiently larger than the current flowing through the second switching element 12 in the steady state of the switching regulate control. That is, it is a value larger than the maximum value of the current flowing through the second switching element 12 in a stable state where the on-duty of the second switching element 12 hardly changes.

The detection of the potential difference does not necessarily have to monitor the voltage across the resistor. That is, when one end of the resistor has a constant voltage, the potential difference can be detected by monitoring the voltage at the other end of the resistor. Specifically, in FIG. 2, the voltage IS is a ground-referenced voltage. By monitoring this voltage IS, the potential difference between both ends of the second resistor RIS can be detected.

When the light emission control circuit 101 detects that the potential difference between both ends of the second resistor RIS is larger than the threshold value, the light emission control circuit 101 stops the current flowing through the second switching element 12 and then increases the current. This process is called a restart process. Then, the light emission control circuit 101 deactivates at least one of the first control signal DRV and the second control signal GTB when the restart process is performed two or more predetermined times. This process is called a stop process.

FIG. 5 shows a waveform diagram illustrating the operation of the light emission control circuit 101. In the following, the high level is active and the low level is inactive, but the correspondence between active and logical levels is not limited to this.

As shown in FIG. 5, when both ends of the first resistor RCS are not short-circuited, the current ILD rises due to soft start, and the detection voltage DTQ of the current detection circuit 123 rises accordingly.

It is assumed that both ends of the first resistor RCS are short-circuited at time t0. When the detection voltage DTQ drops due to a short circuit, the second drive circuit 120 tries to increase the current ILD flowing through the light emitting element 15, so that the on-duty of the second switching element 12 is increased. Then, the current flowing through the second resistor RIS increases, so that the detection circuit 132 changes the detection signal DETB from a low level to a high level when the potential difference between both ends of the second resistor RIS becomes larger than the threshold value.

When the detection signal DETB reaches a high level, the soft start control circuit 135 soft starts. This soft start corresponds to the restart process. When the soft start is executed, the on-duty of the second switching element 12 decreases, and the current ILD flowing through the light emitting element 15 decreases. Further, the detection signal DETB changes from high level to low level.

Since both ends of the first resistor RCS are short-circuited after the time t0, the detection voltage DTQ of the current detection circuit 123 remains low. The current ILD flowing through the light emitting element 15 gradually increases due to the soft start, but since the detection voltage DTQ of the current detection circuit 123 remains low, the second drive circuit 120 determines that the current ILD remains small, and the second switching element 12 Continue to increase on-duty. Then, since the potential difference between both ends of the second resistor RIS becomes larger than the threshold value again, the detection circuit 132 changes the detection signal DETB from a low level to a high level, and the soft start control circuit 135 performs a soft start. After that, the same operation is repeated.

When the rising edge of the detection signal DETB occurs twice, the operation control circuit 133 changes the stop signal SST from the low level to the high level. When the stop signal SST is at a high level, the second drive circuit 120 turns off the second switching element 12 by lowering the second control signal GTB to a low level. Although the predetermined number of times is set to 2 in FIG. 5, the predetermined number of times is not limited to this and may be 2 or more. Further, in FIG. 5, the stop signal SST is input to the control signal output circuit 121, but the stop signal SST may be input to the first drive circuit 110. In that case, the first drive circuit 110 outputs an inactive first control signal DRV when the stop signal SST is active. As a result, the first switching element 11 is turned off, so that the current flowing through the light emitting element 15 is stopped.

According to this embodiment, even when both ends of the first resistor RCS are short-circuited, the overcurrent flowing through the light emitting element 15 can be stopped based on the potential difference between both ends of the second resistor RIS. That is, the restart process is performed when the potential difference between both ends of the second resistor RIS exceeds the threshold value, but the restart process is repeated when both ends of the first resistor RCS are short-circuited. In the present embodiment, the overcurrent flowing through the light emitting element 15 can be stopped by performing the stop process when the restart process is repeated.

Further, in FIG. 5, the detection signal DETB became high level due to the short circuit at both ends of the first resistor RCS, but as will be described later, the detection signal DETB may become high level one or more times even in the normal state. There is. According to the present embodiment, since the stop process is performed when the restart process by soft start is performed a predetermined number of times of 2 or more, it is possible to prevent the stop process from being executed in the normal state. The predetermined number of times may be set to be larger than the number of times when the detection signal DETB becomes a high level in the normal state.

Further, in the present embodiment, the light emission control circuit 101 PWM-controls the second control signal GTB based on the potential difference between both ends of the first resistor RCS and the potential difference between both ends of the second resistor RIS. The light emission control circuit 101 increases the current flowing through the second switching element 12 by increasing the duty of the second control signal GTB in the restart process. This process is called a soft start process.

Specifically, in the soft start process, the soft start control circuit 135 once lowers the output voltage ERQ of the error amplifier circuit 124, and then gradually raises the output voltage ERQ. As described with reference to FIG. 3, the duty of the second control signal GTB is determined by the ERQ. Therefore, as the output voltage ERQ decreases, the second control signal GTB becomes inactive and the second switching element 12 is turned off. Then, the duty of the second control signal GTB gradually increases as the output voltage ERQ gradually increases. The current flowing through the second switching element 12 is on and off, but when it is averaged over time, the current increases as the on-duty gradually increases.

As will be described later, even when normal, that is, when both ends of the first resistor RCS are not short-circuited, the potential difference between both ends of the second resistor RIS may be larger than the threshold value. When it is detected that the potential difference between both ends of the second resistor RIS is larger than the threshold value, the restart process is performed to return to the normal switching regulated control. On the other hand, when both ends of the first resistor RCS are short-circuited, the restart process is repeated, so that the stop process is performed. As a result, the overcurrent flowing through the light emitting element 15 can be stopped.

Further, in the present embodiment, the light emission control circuit 101 determines that both ends of the first resistor RCS are short-circuited when the restart process is performed a predetermined number of times.

When both ends of the first resistor RCS are short-circuited, the resistance value between both ends of the first resistor RCS differs depending on the short-circuited state, so it is unknown what value the potential difference between both ends of the first resistor RCS will be. Therefore, it is difficult to determine a short circuit based on the potential difference between both ends of the first resistor RCS. According to this embodiment, it can be determined that both ends of the first resistor RCS are short-circuited based on the detection result of the current flowing through the second switching element 12. That is, the restart process is executed when the current flowing through the second switching element 12 exceeds the threshold value. Therefore, by determining the short circuit based on the restart process, both ends of the first resistor RCS are appropriately set. It can be determined that it has been short-circuited.

3. 3. Detailed Configuration Example FIG. 6 is a detailed configuration example of the detection circuit 132. The detection circuit 132 includes a comparator CPB. The comparator CPB compares the voltage IS at one end of the second resistor RIS with the reference voltage VTB, and outputs the detection signal DETB as a result. The reference voltage VTB corresponds to the above-mentioned threshold value, that is, the threshold value for the potential difference across the second resistor RIS. The comparator CPB outputs DETB = L when IS <VTB, and outputs DETB = H when IS> VTB.

FIG. 7 is a detailed configuration example of the operation control circuit 133. The operation control circuit 133 includes a timer TIM, a counter CNCA, a latch circuit FA3, and an AND circuit ANA. The latch circuit FA3 is, for example, a dynamic flip-flop circuit.

FIG. 8 is a waveform diagram illustrating the operation of the operation control circuit 133. The timer TIM is activated at the rising edge of the detection signal DETB, and outputs a signal TMQ that becomes a high level for a predetermined period from the rising edge. When both ends of the first resistor RCS are short-circuited, the soft start process is repeated, but a period longer than the interval is set as a predetermined period of the timer TIM.

The counter CNCA counts the number of restart processes. Specifically, the counter CNCA counts the rising edge of the detection signal DETB during the period when the signal TMQ is at a high level. The counter CNCA includes latch circuits FA1 and FA2. The latch circuits FA1 and FA2 are, for example, dynamic flip-flop circuits.

At the first rising edge of the detection signal DETB, the signal TMQ goes from low level to high level. When the signal TMQ is at a high level, the latch circuits FA1 and FA2 are in the reset release state. The latch circuit FA1 captures a high level at the first rising edge of the detection signal DETB. As a result, the output signal ERR1 of the latch circuit FA1 changes from a low level to a high level.

It is assumed that the rising edge of the second detection signal DETB occurs within the period when the signal TMQ is at a high level. At this time, the latch circuit FA2 captures the high-level output signal ERR1 at the rising edge of the detection signal DETB. As a result, the output signal ERR2 of the latch circuit FA2 changes from low level to high level.

The AND circuit ANA outputs the logical product of the output signals ERR1 and ERR2. When all of the output signals ERR1 and ERR2 go to high level, that is, at the rising edge of the second detection signal DETB in FIG. 8, the output signal ANAQ of the AND circuit ANA goes from low level to high level. When the signal TMQ becomes low level after the predetermined period elapses, the latch circuits FA1 and FA2 are reset, so that the output signals ERR1, ERR2, and ANAQ become low level.

The output signal ANAQ of the AND circuit ANA is input to the clock terminal of the latch circuit FA3. At the rising edge of the output signal ANAQ, the latch circuit FA3 captures a high level. As a result, the stop signal SST output by the latch circuit FA3 changes from low level to high level.

As described above, when the rising edge of the detection signal DETB occurs a predetermined number of times, that is, when the count number of the counter CTAN reaches a predetermined number of times, the stop signal SST changes from a low level to a high level. When the stop signal SST is at a high level, the control signal output circuit 121 deactivates the second control signal GTB. That is, the stop process is performed. Although the predetermined number of times is set to 2 in FIG. 8, the predetermined number of times may be 2 or more.

4. Soft start control circuit The configuration and operation of the soft start control circuit 135 will be described. FIG. 9 is a detailed configuration example of the soft start control circuit 135.

The soft start control circuit 135 includes P-type transistors TP1 to TP3, N-type transistors TN1, TN2, bipolar transistors BPT, an inverter INV, and a current source IBS1.

FIG. 10 shows a waveform diagram illustrating the operation of the soft start control circuit 135. When the detection signal DETB changes from low level to high level, the N-type transistors TN1 and TN2 turn from off to on.

When the N-type transistors TN1 and TN2 are on, the terminals TCM and TSS are connected to the ground via the N-type transistors TN1 and TN2. As a result, the capacitor CM connected to the terminal TCM and the capacitor CSS connected to the terminal TSS are discharged. The capacitors CM and CSS are external components of the light emission control device 100. When the capacitors CM and CSS are discharged, the output voltage ERQ of the error amplifier circuit 124 and the voltage SS of the terminal TSS become a voltage near the ground.

The P-type transistors TP2 and TP3 form a current mirror circuit, and the current flowing through the current source IBS1 is mirrored by the drain current of the P-type transistor TP3. When the detection signal DETB is at a high level, the P-type transistor TP1 is on. At this time, the current flowing through the current source IBS1 flows through the P-type transistor TP1, so that the mirror current is zero.

When the detection signal DETB changes from high level to low level, the N-type transistors TN1 and TN2 turn from on to off.

When the detection signal DETB is low level, the P-type transistor TP1 and the N-type transistors TN1 and TN2 are off. At this time, the current flowing through the current source IBS1 is mirrored by the drain current of the P-type transistor TN3, and the mirror current charges the capacitor CSS, so that the voltage SS gradually rises. When the voltage SS rises, the base-emitter voltage of the bipolar transistor BPT increases, so that the bipolar transistor BPT turns off. As a result, the capacitor CM is charged by the output of the error amplifier circuit 124, and the output voltage ERQ of the error amplifier circuit 124 gradually rises.

FIG. 11 is a waveform diagram when the soft start process is performed in the normal state. After the power is turned on to the light emission control device 100, the voltage SS rises due to the soft start. At this time, it is assumed that the dimming voltage ACS is small, that is, the current ILD flowing through the light emitting element 15 is small.

It is assumed that the dimming voltage ACS suddenly increases when the soft start is completed and the capacitor CSS is sufficiently charged. At this time, since the current ILD flowing through the light emitting element 15 is still small, the detection voltage DTQ of the current detection circuit 123 is lower than the dimming voltage ACS. Therefore, the output voltage ERQ of the error amplifier circuit 124 rises.

As the ERQ increases, the duty of the second control signal GTB increases, so that the on-duty of the second switching element 12 increases, and a large current is supplied to the inductor 14. Then, since the voltage IS at one end of the second resistor RIS becomes large, the detection signal DETB becomes high level, and the restart process, that is, the soft start process is executed.

As described above, the restart process may be executed at least once in the normal state when both ends of the first resistor RCS are not short-circuited.

5. Projection-type image display device FIG. 12 is a configuration example of a projection-type image display device 400 including a light source device 200. The projection type image display device 400 is a device that projects an image on a screen, and is also called a projector. The projection type image display device 400 includes a light source device 200, a processing device 300, an operation unit 310, a storage unit 320, a communication unit 330, a display device 340, and an optical system 350. The light source device 200 includes a light emission control device 100 and a light source circuit 10.

The communication unit 330 communicates with an information processing device such as a PC. The communication unit 330 is various video interfaces such as VGA standard, DVI standard, HDMI (HDMI is a registered trademark) standard and the like. Alternatively, the communication unit 330 may be a communication interface such as a USB standard, or may be a network interface such as a LAN. The storage unit 320 stores the image data input from the communication unit 330. Further, the storage unit 320 may function as a working memory of the processing device 300. The storage unit 320 is various storage devices such as a semiconductor memory or a hard disk drive. The operation unit 310 is a user interface for the user to operate the projection type image display device 400. For example, the operation unit 310 is a button or touch panel, a pointing device, a character input device, or the like. The processing device 300 is a processor such as a CPU or MPU. The processing device 300 transmits the image data stored in the storage unit 320 to the display device 340. Further, the processing device 300 performs dimming control by outputting a PWM signal and a dimming voltage to the light emission control device 100. The display device 340 includes a liquid crystal display panel and a display driver for displaying an image on the liquid crystal display panel based on image data. Light is incident on the liquid crystal panel from the light source circuit 10, and the light transmitted through the liquid crystal panel is projected onto the screen by the optical system 350. In FIG. 12, the light path is indicated by a dotted arrow.

The light emission control device of the present embodiment described above controls the first switching element and the second switching element of the light source circuit. The light source circuit includes a light emitting element, a first resistor, and a first switching element provided in series between the first power supply node and the first node, and an inductor provided in series between the first node and the second power supply node. And a second switching element and a second resistor. The light emission control device includes a detection circuit and a light emission control circuit. The detection circuit detects the potential difference between both ends of the second resistor. The light emission control circuit outputs a first control signal for controlling the on / off of the first switching element and a second control signal for controlling the on / off of the second switching element. When the detection circuit detects that the potential difference between both ends of the second resistor is larger than the threshold value, the light emission control circuit performs a restart process of stopping the current flowing through the second switching element and then increasing the current. The light emission control circuit performs a stop process for deactivating at least one of the first control signal and the second control signal when the restart process is performed two or more predetermined times.

In this way, even when both ends of the first resistor are short-circuited, the overcurrent flowing through the light emitting element can be stopped based on the potential difference between both ends of the second resistor. That is, the restart process is performed when the potential difference between both ends of the second resistor exceeds the threshold value, but the restart process is repeated when both ends of the first resistor are short-circuited. According to the present embodiment, the overcurrent flowing through the light emitting element can be stopped by performing the stop process when the restart process is repeated.

Further, in the present embodiment, the light emission control circuit may have a counter that counts the number of restart processes. The light emission control circuit may perform stop processing when the number of counts of the counter reaches a predetermined number of times.

According to the present embodiment, the count number of counters is the number of restart processes, and when the number of times reaches a predetermined number, the stop process is performed. As a result, at least one of the first control signal and the second control signal can be deactivated when the restart process is performed two or more predetermined times.

Further, in the present embodiment, the light emission control circuit may perform PWM control of the second control signal based on the potential difference between both ends of the first resistor and the potential difference between both ends of the second resistor. In the restart process, the light emission control circuit may perform a soft start process of increasing the current flowing through the second switching element by increasing the duty of the second control signal.

In the normal state where both ends of the first resistor are not short-circuited, the potential difference between both ends of the second resistor may be larger than the threshold value. When it is detected that the potential difference between both ends of the second resistor is larger than the threshold value, the restart process is performed by the soft start process, so that the normal switching regulate control can be restored. On the other hand, when both ends of the first resistor are short-circuited, the restart process is repeated, so that the stop process is performed. As a result, the overcurrent flowing through the light emitting element can be stopped.

Further, in the present embodiment, the light emission control circuit may determine that both ends of the first resistor are short-circuited when the restart process is performed a predetermined number of times.

When both ends of the first resistor are short-circuited, the resistance value between both ends of the first resistor differs depending on the state of the short circuit, so it is unknown what the potential difference between both ends of the first resistor will be. Therefore, it is difficult to determine a short circuit based on the potential difference between both ends of the first resistor. According to this embodiment, it can be determined that both ends of the first resistor are short-circuited based on the detection result of the current flowing through the second switching element. That is, since the restart process is executed when the current flowing through the second switching element exceeds the threshold value, both ends of the first resistor are appropriately short-circuited by determining the short circuit based on the restart process. You can judge that.

Further, in the present embodiment, when the detection circuit detects that the potential difference between both ends of the second resistor is larger than the threshold value, the light emission control circuit may determine that an overcurrent has flowed through the second switching element.

In this way, it is possible to determine whether or not an overcurrent has flowed through the second switching element both when both ends of the first resistor are short-circuited and when both ends of the first resistor are not short-circuited.

Further, in the present embodiment, the light emission control circuit may include a current detection circuit that detects a current flowing through the light emitting element based on the potential difference between both ends of the first resistor. The light emission control circuit may PWM control the second control signal based on the detection result from the current detection circuit and the potential difference between both ends of the second resistor.

In this way, the current flowing through the light emitting element can be controlled by switching regulation based on the detection result of the current flowing through the light emitting element and the detection result of the current flowing through the second switching element. Then, even when both ends of the first resistor are short-circuited, the overcurrent can be appropriately dealt with by using the detection result of the current flowing through the second switching element.

Further, in the present embodiment, the light source device includes the light emission control device according to any one of the above and the light source circuit.

Further, in the present embodiment, the first resistor may be connected between the first power supply node and one end of the light emitting element. The first switching element may be connected between the other end of the light emitting element and one end of the inductor. The second switching element may be connected between the other end of the inductor and one end of the second resistor. The other end of the second resistor may be connected to the second power supply node.

Further, the projection type image display device of the present embodiment includes the light source device described in any of the above and a processing device for controlling the light source device.

Although the present embodiment has been described in detail as described above, those skilled in the art will easily understand that many modifications that do not substantially deviate from the novel matters and effects of the present disclosure are possible. Therefore, all such variations are included in the scope of the present disclosure. For example, a term described at least once in a specification or drawing with a different term in a broader or synonymous manner may be replaced by that different term anywhere in the specification or drawing. All combinations of the present embodiment and modifications are also included in the scope of the present disclosure. Further, the configuration and operation of the light emission control circuit, the light emission control device, the light source circuit, the light source device, the projection type image display device, and the like are not limited to those described in the present embodiment, and various modifications can be performed.

10 ... light source circuit, 11 ... first switching element, 12 ... second switching element, 14 ... inductor, 15 ... light emitting element, 100 ... light emission control device, 101 ... light emission control circuit, 110 ... first drive circuit, 120 ... first 2 drive circuit, 121 ... control signal output circuit, 122 ... slope compensation circuit, 123 ... current detection circuit, 124 ... error amplifier circuit, 125 ... switch circuit, 126 ... comparator, 132 ... detection circuit, 133 ... operation control circuit, 135 ... Soft start control circuit, 140 ... Oscillation circuit, 200 ... Light source device, 300 ... Processing device, 310 ... Operation unit, 320 ... Storage unit, 330 ... Communication unit, 340 ... Display device, 350 ... Optical system, 400 ... Projection Type image display device, ACS ... Dimming voltage, DCS ... PWM signal, DRV ... 1st control signal, GTB ... 2nd control signal, ILD ... Current flowing through the light emitting element, N1 ... 1st node, NGN ... 2nd power supply Node, NVI ... 1st power supply node, RCS ... 1st resistance, RIS ... 2nd resistance

Claims (9)

A light emitting element, a first resistor, and a first switching element provided in series between the first power supply node and the first node, and an inductor and a second in series provided between the first node and the second power supply node. A light emission control device that controls the first switching element and the second switching element of the light source circuit including the switching element and the second resistor.
A detection circuit that detects the potential difference between both ends of the second resistor,
A light emission control circuit that outputs a first control signal that controls on / off of the first switching element and a second control signal that controls on / off of the second switching element.
Including
The light emission control circuit
When the detection circuit detects that the potential difference between both ends of the second resistor is larger than the threshold value, a restart process is performed to increase the current after stopping the current flowing through the second switching element.
A light emission control device characterized in that when the restart process is performed two or more predetermined times, a stop process for inactivating at least one of the first control signal and the second control signal is performed. In the light emission control device according to claim 1,
The light emission control circuit
It has a counter that counts the number of times of the restart process.
A light emitting control device characterized in that the stop processing is performed when the count number of times of the counter reaches the predetermined number of times. In the light emission control device according to claim 1 or 2.
The light emission control circuit
The second control signal is PWM controlled based on the potential difference between both ends of the first resistor and the potential difference between both ends of the second resistor.
A light emission control device characterized in that, in the restart process, a soft start process is performed in which the duty of the second control signal is increased to increase the current flowing through the second switching element. In the light emission control device according to any one of claims 1 to 3.
The light emission control circuit
A light emission control device, characterized in that it is determined that both ends of the first resistor are short-circuited when the restart process is performed a predetermined number of times. In the light emission control device according to any one of claims 1 to 4.
The light emission control circuit
A light emission control device, characterized in that, when the detection circuit detects that the potential difference between both ends of the second resistor is larger than the threshold value, it is determined that an overcurrent has flowed through the second switching element. In the light emission control device according to claim 1 or 2.
The light emission control circuit
A current detection circuit for detecting a current flowing through the light emitting element based on a potential difference between both ends of the first resistor is included.
The light emission control circuit
A light emission control device characterized in that the second control signal is PWM-controlled based on the detection result from the current detection circuit and the potential difference between both ends of the second resistor. In the light emission control device according to any one of claims 1 to 6.
With the light source circuit
With the light emission control device
A light source device characterized by including. In the light source device according to claim 7.
The first resistor is connected between the first power supply node and one end of the light emitting element.
The first switching element is connected between the other end of the light emitting element and one end of the inductor.
The second switching element is connected between the other end of the inductor and one end of the second resistor.
A light source device characterized in that the other end of the second resistor is connected to the second power supply node. The light source device according to claim 7 or 8.
A processing device that controls the light source device and
A projection type image display device characterized by including.

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