Failure detection circuit and imaging device

Abstract

To provide a failure detection circuit capable of suppressing an increase in circuit scale.SOLUTION: A failure detection circuit (11) includes three detection circuit sections (111a, 111b and 111c) that are provided to light emitting elements (D1, D2 and D3), respectively, which each are an IR-LED, each detection circuit section detecting a voltage (Vf) across the light emitting element corresponding thereto. The outputs of the detection circuit sections (111a, 111b and 111c) are wired to one output terminal (2a), and signals are output from the output terminal (2a), a signal in the case where at least one of the light emitting elements (D1, D2 and D3) fails being different from a signal in the case where all of the light emitting elements (D1, D2 and D3) do not fail.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a failure detection circuit and an imaging device including the same. [Background technology]

[0002] Driver monitoring systems (hereinafter referred to as DMS) for ensuring the safety of automobile occupants have become widespread. DMSs generally recognize the state of occupants by performing image analysis on images of the occupants captured using infrared light. An imaging device for capturing an image of an occupant, for example, illuminates the occupant as a subject with infrared light emitted from a light source and captures an image of the illuminated occupant using an image sensor.

[0003] The light source provided in the imaging device is made up of multiple infrared light emitting diodes (hereinafter referred to as IR-LEDs) connected in series. If one of the multiple IR-LEDs goes out due to a short circuit, the light source as a whole continues to emit light even though the preset light distribution is not met, so the outage may go unnoticed.

[0004] For example, Patent Document 1 describes a lighting control device that does not detect failures in the IR-LEDs used to capture images of occupants in a DMS, but detects failures in multiple LEDs that make up a vehicle headlamp. In this lighting control device, a Vf detection circuit is connected in parallel to both ends of each of multiple LEDs connected in series. By comparing the forward voltages Vf periodically detected by these Vf detection circuits, a short circuit that has occurred in any of the multiple LEDs is detected. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-011872 Summary of the Invention [Problem to be solved by the invention]

[0006] The conventional technology described in Patent Document 1 acquires the forward voltages of a plurality of light-emitting elements and detects a fault occurring in any of the plurality of light-emitting elements based on the results of comparing these voltages. For this reason, the conventional technology requires providing a plurality of output terminals for outputting detection signals for each light-emitting element to a microcontroller (hereinafter referred to as MCU) that detects a fault in the light-emitting element based on the forward voltage detection signals, which poses a problem of increasing the size of the circuit. In particular, the lighting control device described in Patent Document 1 is configured with a relatively large circuit designed to control the lighting of vehicle headlamps, and therefore an increase in circuit size due to the provision of multiple output terminals for outputting detection signals for each light-emitting element is acceptable. However, since the circuit that detects failures in the IR-LEDs used to capture images of occupants in the DMS may be installed in a small imaging device, it is necessary to suppress the increase in circuit size.

[0007] The present disclosure is intended to solve the above-mentioned problems, and has an object to provide a fault detection circuit that can suppress an increase in the circuit size. [Means for solving the problem]

[0008] The fault detection circuit of the present disclosure comprises a plurality of detection circuit units provided for each of a plurality of light-emitting elements, each detecting the voltage across the corresponding light-emitting element, the outputs of the plurality of detection circuit units being connected to a single output terminal, and outputting different signals from the output terminal when a fault occurs in at least one of the plurality of light-emitting elements and when no fault occurs in any of the plurality of light-emitting elements. [Effects of the Invention]

[0009] According to the present disclosure, the outputs of a plurality of detection circuit units that detect the voltages across the light-emitting elements are connected to a single output terminal, and different signals are output from the output terminal when a fault occurs in at least one of the plurality of light-emitting elements and when none of the plurality of light-emitting elements has a fault. Because it is possible to recognize that a fault has occurred in at least one of the plurality of light-emitting elements from the signal output from the single output terminal, the fault detection circuit according to the present disclosure can prevent an increase in the circuit size. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a block diagram showing an example of the configuration of an imaging device according to a first embodiment. [Figure 2] 1 is a circuit diagram showing a configuration example of a failure detection circuit according to a first embodiment. [Figure 3] FIG. 3 is a waveform diagram showing a voltage waveform of an infrared light emitting diode that constitutes a light source. [Figure 4] 3 is a waveform diagram showing voltage waveforms at various points in the failure detection circuit according to the first embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Embodiment 1 FIG. 1 is a block diagram showing an example of the configuration of an imaging device 1 according to a first embodiment. In FIG. 1, the imaging device 1 is, for example, a device constituting a DMS mounted on a vehicle, and illuminates a vehicle driver with infrared light and captures an image of the illuminated driver. The imaging device 1 is connected to an MCU 2 via a signal line. The MCU 2 controls the imaging process of the imaging device 1 by executing a control program stored in a memory (not shown in FIG. 1). For example, the MCU 2 determines whether a short-circuit fault has occurred in the light source based on a voltage detection signal output from a fault detection circuit 11.

[0012] As shown in FIG. 1, the imaging device 1 includes a fault detection circuit 11, light-emitting elements D1, D2, and D3, a drive circuit 12, and an image sensor 13. The fault detection circuit 11 detects short-circuit faults in the light-emitting elements D1, D2, and D3. The fault detection circuit 11 is connected to an MCU 2 via one output terminal 2a. A voltage detection signal detected by the fault detection circuit 11 is output to the MCU 2 via the output terminal 2a. The fault detection circuit 11 is further connected to a drive circuit 12 via an input terminal 12a and an output terminal 12b. By being connected to the drive circuit 12 via the input terminal 12a and the output terminal 12b, the fault detection circuit 11 forms a closed circuit with the drive circuit 12.

[0013] Light-emitting elements D1, D2, and D3 are IR-LEDs that constitute an infrared light source that emits illumination light. The IR-LED light-emitting elements D1, D2, and D3 are light-emitting diodes that emit near-infrared illumination light. As shown in Figure 1, the light-emitting elements D1, D2, and D3 are connected in series. When an LED current flows through a closed circuit, the light-emitting elements D1, D2, and D3 emit near-infrared light for imaging, generating a forward voltage Vf.

[0014] 1 shows a case where there are three IR-LEDs, but the imaging device 1 is not limited to this. For example, the number of IR-LEDs connected in series in the imaging device 1 may be any number, such as four or more. Furthermore, the light source made up of IR-LEDs may be configured integrally with the imaging device 1, or may be provided externally (for example, detachably) to the imaging device 1 via any connection means (not shown).

[0015] The drive circuit 12 supplies LED current to the light-emitting elements D1, D2, and D3 to cause them to emit light. By passing the LED current through the light-emitting elements D1, D2, and D3, the drive circuit 12 generates a forward voltage Vf between the anode and cathode of each of the light-emitting elements D1, D2, and D3, thereby driving the light-emitting elements D1, D2, and D3. The LED current is a square wave supplied to the light-emitting elements D1, D2, and D3 in synchronization with a flash signal. The flash signal is a square wave sent from the image sensor 13, and the image sensor 13 captures an image of the subject while the light source is illuminating the subject.

[0016] The image sensor 13 is an imaging element that captures an image of a subject. For example, the image sensor 13 is a CMOS (Complementary Metal Oxide Semiconductor) image sensor, which is a solid-state imaging element. The image sensor 13 also outputs a flash signal, which is a square wave, and captures an image of the subject when the flash signal is at a high level, for example.

[0017] Fig. 2 is a circuit diagram showing an example configuration of the fault detection circuit 11. In Fig. 2, the fault detection circuit 11 includes a detection circuit unit 111a, a detection circuit unit 111b, and a detection circuit unit 111c. The outputs of the detection circuit unit 111a, the detection circuit unit 111b, and the detection circuit unit 111c are each connected to a single output terminal 2a. A detection circuit unit is provided for each IR-LED, so there are multiple detection circuit units, and the number may be four or more depending on the number of IR-LEDs.

[0018] The detection circuit unit 111a includes resistors R1a, R2a, R3a, R4a, R5a, and R6a, and transistors T1a, T2a, and T3a. Similarly, the detection circuit unit 111b includes resistors R1b, R2b, R3b, R4b, R5b, and R6b, and transistors T1b, T2b, and T3b. The detection circuit unit 111c includes resistors R1c, R2c, R3c, R4c, R5c, and R6c, and transistors T1c, T2c, and T3c.

[0019] (Detection circuit section 111a) The resistor R1a is a first resistor having one terminal connected to the cathode of the light-emitting element D1 and one terminal connected to the resistor R2a and the gate terminal of the transistor T1a. The resistor R2a is a second resistor having the other terminal connected to the anode of the light-emitting element D1 and the gate and source terminals of the transistor T1a. The forward voltage Vf, which is the voltage across the light-emitting element D1, is resistively divided by the resistors R1a and R2a. The resistors R1a and R2a are provided to divide the forward voltage Vf so that it does not exceed the rated voltage between the gate and source terminals of the transistor T1a. The resistor R2a is provided to stabilize the potential of the gate terminal of the transistor T1a.

[0020] The transistor T1a is a P-channel field-effect transistor, such as a Pch-MOSFET. When an LED current flows through the normal light-emitting element D1, a forward voltage Vf is generated between the anode and cathode of the light-emitting element D1. The forward voltage Vf is resistively divided by the resistor elements R1a and R2a, and the resulting voltage is applied between the gate and source terminals of the transistor T1a. At this time, the potential of the gate terminal of the transistor T1a becomes lower than the potential of the source terminal. As a result, the voltage between the gate and source terminals exceeds the threshold voltage, turning on the transistor T1a.

[0021] The resistor R3a is a third resistor element, with one terminal connected to the drain terminal of the transistor T1a and the other terminal connected to one terminal of the resistor R4a and the gate terminal of the transistor T2a. The other terminal of the resistor R4a is grounded and is connected to the ground potential GND. The resistors R3a and R4a are provided to divide the voltage generated on the drain terminal side of the transistor T1a so that it does not exceed the rated voltage between the gate terminal and source terminal of the transistor T2a. The resistor R4a is connected to the ground potential GND so that the potential of the gate terminal of the transistor T2a does not become unstable.

[0022] The transistors T2a and T3a form a two-stage output-side switching element group. The transistor T2a is a first N-channel field-effect transistor, such as an Nch-MOSFET. The transistor T2a has a gate terminal grounded via a fourth resistor R4a, a source terminal directly grounded, and a drain terminal connected to the power supply Vcc via a resistor R5a.

[0023] The transistor T3a is a second N-channel field-effect transistor (e.g., an Nch-MOSFET) that serves as an output-side switching element. The gate terminal of the transistor T3a is connected to the drain terminal of the transistor T2a, the source terminal is grounded, and the drain terminal is connected to the power supply Vcc via the resistor R6a. The drain terminal of the transistor T2a is connected to the output terminal 2a.

[0024] Transistor T2a turns on in synchronization with the timing when transistor T1a turns on. When transistor T2a turns on, its drain terminal goes low, for example, to ground potential GND. At this time, the potential at the gate terminal of the subsequent transistor T3a also goes low, turning it off. Resistors R5a and R6a are provided to pull up the voltage supplied from power supply Vcc.

[0025] The voltage supplied from the power supply Vcc is the power supply voltage for a device, such as the MCU2, that receives the voltage detection signal from the fault detection circuit 11. The potential of the drain terminal of transistor T3a is pulled up to the voltage from the power supply Vcc by resistor R6a, i.e., it is an open drain. When the LED current is high, the voltage detection signal output from the drain terminal of transistor T3a goes high, and when the LED current is low, the voltage detection signal output from the drain terminal of transistor T3a goes low. By repeating this operation, the voltage detection signal output from the drain terminal of transistor T3a becomes a square wave synchronized with the LED current.

[0026] (Detection circuit section 111b) The resistor R1b is a first resistor having one terminal connected to the cathode of the light-emitting element D2 and one terminal connected to the resistor R2b and the gate terminal of the transistor T1b. The resistor R2b is a second resistor having the other terminal connected to the anode of the light-emitting element D2 and the gate and source terminals of the transistor T1b. The forward voltage Vf, which is the voltage across the light-emitting element D2, is resistively divided by the resistors R1b and R2b. The resistors R1b and R2b are provided to divide the forward voltage Vf so that it does not exceed the rated voltage between the gate and source terminals of the transistor T1b. The resistor R2b is provided to stabilize the potential of the gate terminal of the transistor T1b.

[0027] Transistor T1b is a P-channel field-effect transistor, such as a Pch-MOSFET. When an LED current flows through light-emitting element D2 in a normal state, a forward voltage Vf is generated between the anode and cathode of light-emitting element D2. The forward voltage Vf is divided by resistors R1b and R2b, and the resulting voltage is applied between the gate and source terminals of transistor T1b. At this time, the potential of the gate terminal of transistor T1b becomes lower than the potential of the source terminal. As a result, the voltage between the gate and source terminals exceeds the threshold voltage, turning transistor T1b on.

[0028] Resistor R3b is a third resistor element, with one terminal connected to the drain terminal of transistor T1b and the other terminal connected to resistor R4b and the gate terminal of transistor T2b. Resistor R4b has the other terminal grounded, which is the ground potential GND. Resistors R3b and R4b are provided to divide the voltage generated at the drain terminal of transistor T1b so that it does not exceed the rated voltage between the gate and source terminals of transistor T2b. Resistor R4b is connected to ground potential GND to prevent the potential at the gate terminal of transistor T2b from becoming unstable.

[0029] Transistors T2b and T3b form a two-stage output-side switching element group. Transistor T2b is a first N-channel field-effect transistor, such as an Nch-MOSFET. Transistor T2b has a gate terminal grounded via a fourth resistor R4b, a source terminal directly grounded, and a drain terminal connected to power supply Vcc via resistor R5b.

[0030] The transistor T3b is a second N-channel field-effect transistor (e.g., an Nch-MOSFET) that serves as an output-side switching element. The gate terminal of the transistor T3b is connected to the drain terminal of the transistor T2b, the source terminal is grounded, and the drain terminal is connected to the power supply Vcc via the resistor R6b. The drain terminal of the transistor T2b is connected to the output terminal 2a.

[0031] Transistor T2b turns on in synchronization with the timing when transistor T1b turns on. When transistor T2b turns on, its drain terminal goes low, for example, to ground potential GND. At this time, the potential at the gate terminal of the subsequent transistor T3b also goes low, turning it off. Resistors R5b and R6b are provided to pull up the voltage supplied from the power supply Vcc.

[0032] The voltage supplied from the power supply Vcc is the power supply voltage for a device, such as the MCU2, that receives the voltage detection signal from the fault detection circuit 11. The potential of the drain terminal of transistor T3b is pulled up to the voltage from the power supply Vcc by resistor R6b, i.e., it is an open drain. When the LED current is high, the voltage detection signal output from the drain terminal of transistor T3b goes high, and when the LED current is low, the voltage detection signal output from the drain terminal of transistor T3b goes low. By repeating this operation, the voltage detection signal output from the drain terminal of transistor T3b becomes a square wave synchronized with the LED current.

[0033] (Detection circuit section 111c) The resistor R1c is a first resistor having one terminal connected to the cathode of the light-emitting element D3 and one terminal connected to the resistor R2c and the gate terminal of the transistor T1c. The resistor R2c is a second resistor having the other terminal connected to the anode of the light-emitting element D3 and the gate and source terminals of the transistor T1c. The forward voltage Vf, which is the voltage across the light-emitting element D3, is resistively divided by the resistors R1c and R2c. The resistors R1c and R2c are provided to divide the forward voltage Vf so that it does not exceed the rated voltage between the gate and source terminals of the transistor T1c. The resistor R2c is provided to stabilize the potential of the gate terminal of the transistor T1c.

[0034] Transistor T1c is a P-channel field-effect transistor, such as a Pch-MOSFET. When an LED current flows through light-emitting element D3 in a normal state, a forward voltage Vf is generated between the anode and cathode of light-emitting element D3. The forward voltage Vf is divided by resistors R1c and R2c, and the resulting voltage is applied between the gate and source terminals of transistor T1c. At this time, the potential of the gate terminal of transistor T1c becomes lower than the potential of the source terminal. As a result, the voltage between the gate and source terminals exceeds the threshold voltage, turning transistor T1c on.

[0035] Resistor R3c is a third resistor element, with one terminal connected to the drain terminal of transistor T1c and the other terminal connected to resistor R4c and the gate terminal of transistor T2c. Resistor R4c has the other terminal grounded, which is the ground potential GND. Resistors R3c and R4c are provided to divide the voltage generated on the drain terminal side of transistor T1c so that it does not exceed the rated voltage between the gate and source terminals of transistor T2c. Resistor R4c is connected to ground potential GND to prevent the potential of the gate terminal of transistor T2c from becoming unstable.

[0036] Transistors T2c and T3c form a two-stage output-side switching element group. Transistor T2c is a first N-channel field-effect transistor, such as an Nch-MOSFET. Transistor T2c has a gate terminal grounded via a fourth resistor R4c, a source terminal directly grounded, and a drain terminal connected to power supply Vcc via resistor R5c.

[0037] The transistor T3c is a second N-channel field-effect transistor (e.g., an Nch-MOSFET) that serves as an output-side switching element. The gate terminal of the transistor T3c is connected to the drain terminal of the transistor T2c, the source terminal is grounded, and the drain terminal is connected to the power supply Vcc via the resistor R6c. The drain terminal of the transistor T2c is connected to the output terminal 2a.

[0038] Transistor T2c turns on in synchronization with the timing when transistor T1c turns on. When transistor T2c turns on, its drain terminal goes low, for example, to ground potential GND. At this time, the potential at the gate terminal of the subsequent transistor T3c also goes low, turning it off. Resistors R5c and R6c are provided to pull up the voltage supplied from the power supply Vcc.

[0039] The voltage supplied from the power supply Vcc is the power supply voltage for a device, such as the MCU2, that receives the voltage detection signal from the fault detection circuit 11. The potential of the drain terminal of transistor T3c is pulled up to the voltage from the power supply Vcc by resistor R6c, i.e., it is an open drain. When the LED current is high, the voltage detection signal output from the drain terminal of transistor T3c goes high, and when the LED current is low, the voltage detection signal output from the drain terminal of transistor T3c goes low. By repeating this operation, the voltage detection signal output from the drain terminal of transistor T3c becomes a square wave synchronized with the LED current.

[0040] Fig. 3 is a waveform diagram showing the voltage waveforms of light-emitting elements D1, D2, and D3, which are infrared light-emitting diodes that constitute the light source. The voltage waveforms shown in Fig. 3 are the result of a simulation performed using LTspice (registered trademark), a simulation model, in which a forward voltage Vf is generated in each of the light-emitting elements D1, D2, and D3 that constitute the light source when an LED current is passed through the light source provided in the imaging device 1. When the light-emitting elements D1, D2, and D3 are in a normal state, a square-wave forward voltage Vf synchronized with the LED current as shown in Fig. 3 is generated in each of the light-emitting elements D1, D2, and D3 when a square-wave LED current is passed through them.

[0041] For example, if a short circuit occurs in light-emitting element D1 at short-circuit failure occurrence time TS, conduction occurs between the anode and cathode of light-emitting element D1, and no forward voltage Vf is generated even though an LED current flows. For example, in Figure 3, after the short-circuit failure occurrence time TS, no square-wave forward voltage Vf is generated across both ends of light-emitting element D1. On the other hand, even after the short-circuit failure occurrence time TS, a square-wave forward voltage Vf is generated in light-emitting elements D2 and D3, which are in a normal state, due to the flow of LED current.

[0042] Fig. 4 is a waveform diagram showing voltage waveforms at points A, B, C, and D of the fault detection circuit 11. The voltage waveforms shown in Fig. 4 are the results obtained at the detection circuit units 111a, 111b, and 111c and the output terminal 2a by using LTspice to simulate the operation of the fault detection circuit 11 when an LED current is passed through the light source provided in the imaging device 1. Point A is the connection point between the resistor elements R3a and R4a in the detection circuit unit 111a, point B is the connection point between the resistor elements R3b and R4b in the detection circuit unit 111b, and point C is the connection point between the resistor elements R3c and R4c in the detection circuit unit 111c. Point D is an output point where the outputs of detection circuit section 111a, detection circuit section 111b, and detection circuit section 111c are connected together.

[0043] When the voltage obtained by dividing the forward voltage Vf by resistors R1a and R2a is applied between the gate and source terminals of transistor T1a, the voltage between the gate and source terminals of transistor T1a exceeds the threshold voltage, and the potential of the gate terminal becomes lower than the potential of the source terminal of transistor T1a. This turns on transistor T1a, and the square wave voltage waveform shown in Figure 4 appears at point A on the drain terminal side. The voltage at point A on the drain terminal side is applied to the gate terminal of transistor T2a, and transistor T2a turns on when the potential at point A is high.

[0044] Similarly, when the voltage obtained by dividing the forward voltage Vf by resistors R1b and R2b is applied between the gate and source terminals of transistor T1b, the voltage between the gate and source terminals of transistor T1b exceeds the threshold voltage, and the potential of the gate terminal becomes lower than the potential of the source terminal of transistor T1b. This turns on transistor T1b, and the square wave voltage waveform shown in Figure 4 appears at point B on the drain terminal side. The voltage at point B on the drain terminal side is applied to the gate terminal of transistor T2b, and transistor T2b turns on when the potential at point B is high.

[0045] When the voltage obtained by dividing the forward voltage Vf by resistors R1c and R2c is applied between the gate and source terminals of transistor T1c, the voltage between the gate and source terminals of transistor T1c exceeds the threshold voltage, and the potential of the gate terminal becomes lower than the potential of the source terminal of transistor T1c. This turns on transistor T1c, and the square wave voltage waveform shown in Figure 4 appears at point C on the drain terminal side. The voltage at point C on the drain terminal side is applied to the gate terminal of transistor T2c, and transistor T2c turns on when the potential at point C is high.

[0046] In the fault detection circuit 11, the open-drain outputs of transistors T3a, T3b, and T3c are connected in parallel, and these outputs are connected together at the output terminal 2a. When the light-emitting elements D1, D2, and D3 are normal, square-wave voltage waveforms as shown in FIG. 4 are obtained at points A, B, and C. A voltage detection signal having a voltage waveform that alternates between high and low levels in synchronization with these voltage waveforms is output from point D of the output terminal 2a. Note that the simulation shown in FIG. 4 assumes the resistance values ​​of the resistive elements to be constants, but in reality, tuning is required for each circuit.

[0047] Meanwhile, fault detection circuit 11 outputs different signals from output terminal 2a depending on whether a short-circuit fault has occurred in at least one of light-emitting elements D1, D2, and D3 or whether none of light-emitting elements D1, D2, and D3 has a fault. For example, when none of light-emitting elements D1, D2, and D3 has a fault, fault detection circuit 11 outputs a voltage detection signal having a high-level voltage synchronized with the LED current from output terminal 2a. When a short-circuit fault has occurred in at least one of light-emitting elements D1, D2, and D3, a low-level voltage detection signal is constantly output from output terminal 2a.

[0048] As shown in Figure 4, for example, if a short circuit occurs in light-emitting element D1 at short-circuit fault occurrence time TS, a low-level voltage detection signal continues to be output from output terminal 2a. That is, no forward voltage Vf is generated between the anode and cathode of light-emitting element D1. Therefore, no potential difference is generated between the gate terminal and source terminal of transistor T1a, and transistor T1a continues to be off. At this time, transistor T3a, which is the output-side switching element of the two-stage configuration, continues to be on, and a low-level voltage detection signal is output from output terminal 2a.

[0049] The voltage detection signal is output to the MCU 2 via the output terminal 2a. The MCU 2 determines whether a short-circuit fault has occurred in the light source based on the voltage detection signal. For example, if the voltage detection signal output from the output terminal 2a is at a high level, the MCU 2 determines that a short-circuit fault has not occurred in any of the light-emitting elements D1, D2, and D3 that constitute the light source provided in the imaging device 1, and if the voltage detection signal is at a low level, the MCU 2 determines that a short-circuit fault has occurred in one of the light-emitting elements D1, D2, and D3. In this way, the fault detection circuit 11 can determine whether a fault has occurred in any of the light-emitting elements D1, D2, and D3 based on the voltage detection signal acquired via one output terminal 2a.

[0050] Furthermore, the switching elements included in each of the detection circuit units 111a, 111b, and 111c may be Pch-MOSFETs and Nch-MOSFETs as described above, but may also be other switching elements.

[0051] As described above, fault detection circuit 11 according to embodiment 1 includes three detection circuit units 111a, 111b, and 111c, each of which is provided for one of IR-LED light-emitting elements D1, D2, and D3. Each detection circuit unit detects a forward voltage Vf, which is the voltage across the corresponding light-emitting element. The outputs of detection circuit units 111a, 111b, and 111c are connected to a single output terminal 2a, which outputs different signals when a fault occurs in at least one of light-emitting elements D1, D2, and D3 and when none of light-emitting elements D1, D2, and D3 are fault-free. Because a fault in at least one of light-emitting elements D1, D2, and D3 can be detected by the signal output from a single output terminal 2a, fault detection circuit 11 can minimize an increase in circuit size.

[0052] In the fault detection circuit 11 according to the first embodiment, the light-emitting elements D1, D2, and D3 are connected in series. The detection circuit units 111a, 111b, and 111c each include at least N-channel MOSFET transistors T3a, T3b, and T3c, which output high-level and low-level signals depending on whether or not the IR-LED forward voltage Vf is present. The outputs of the transistors T3a, T3b, and T3c are connected to a single output terminal 2a. When a fault occurs in at least one of the light-emitting elements D1, D2, and D3, the output terminal 2a outputs a low-level signal. When a fault occurs in none of the light-emitting elements D1, D2, and D3, the output terminal 2a outputs a high-level signal. Since the occurrence of a failure in at least one of the light-emitting elements D1, D2, and D3 can be recognized by a signal output from one output terminal 2a, the failure detection circuit 11 can prevent an increase in the circuit size.

[0053] In the fault detection circuit 11 according to the first embodiment, each of the detection circuit units 111a, 111b, and 111c includes resistive elements R1a, R1b, and R1c, resistive elements R2a, R2b, and R2c, resistive elements R3a, R3b, and R3c, resistive elements R4a, R4b, and R4c, resistive elements R5a, R5b, and R5c, resistive elements R6a, R6b, and R6c, transistors T1a, T1b, and T1c, transistors T2a, T2b, and T2c, and transistors T3a, T3b, and T3c. The forward voltage Vf is resistively divided by resistors R1a and R2a and applied between the gate and source terminals of transistor T1a. The voltage generated at the drain terminal of transistor T1a is resistively divided by resistors R3a and R4a and applied between the gate and source terminals of transistor T2a. The gate terminal of transistor T2a is grounded via resistor R4a, the source terminal is directly grounded, and the drain terminal is connected to power supply Vcc via resistor R5a. The voltage generated at the drain terminal of transistor T2a is applied between the gate and source terminals of transistor T3a, and the drain terminal of transistor T3a is pulled up to the voltage supplied from power supply Vcc by resistor R6a. The forward voltage Vf is resistively divided by resistors R1b and R2b and applied between the gate and source terminals of transistor T1b. The voltage generated at the drain terminal of transistor T1b is resistively divided by resistors R3b and R4b and applied between the gate and source terminals of transistor T2b. The gate terminal of transistor T2b is grounded via resistor R4b, the source terminal is directly grounded, and the drain terminal is connected to power supply Vcc via resistor R5b. The voltage generated at the drain terminal of transistor T2b is applied between the gate and source terminals of transistor T3b, and the drain terminal of transistor T3b is pulled up to the voltage supplied from power supply Vcc by resistor R6b. The forward voltage Vf is resistively divided by resistors R1c and R2c and applied between the gate and source terminals of transistor T1c. The voltage generated at the drain terminal of transistor T1c is resistively divided by resistors R3c and R4c and applied between the gate and source terminals of transistor T2c. The gate terminal of transistor T2c is grounded via resistor R4c, the source terminal is directly grounded, and the drain terminal is connected to power supply Vcc via resistor R5c. The voltage generated at the drain terminal of transistor T2c is applied between the gate and source terminals of transistor T3c, and the drain terminal of transistor T3c is pulled up to the voltage supplied from power supply Vcc by resistor R6c. The drain terminals of the transistors T3a, T3b, and T3c included in the detection circuit sections 111a, 111b, and 111c are connected to one output terminal 2a. Since the occurrence of a failure in at least one of the light-emitting elements D1, D2, and D3 can be recognized by a signal output from one output terminal 2a, the failure detection circuit 11 can prevent an increase in the circuit size.

[0054] The imaging device 1 according to the first embodiment includes an image sensor 13 that captures an image of a subject, a light source in which light-emitting elements D1, D2, and D3 that are IR-LEDs for illuminating the subject are connected in series, a drive circuit 12 that supplies LED current to the light-emitting elements D1, D2, and D3 to cause the IR-LEDs to emit light, and a fault detection circuit 11. With this configuration, it is possible to provide an imaging device 1 that includes a fault detection circuit 11 that does not increase in size.

[0055] Any of the components of the embodiments may be modified or omitted. [Explanation of symbols]

[0056] 1 imaging device, 2 MCU, 2a output terminal, 11 fault detection circuit, 12 drive circuit, 12a input terminal, 12b output terminal, 13 image sensor, 111a, 111b, 111c detection circuit section, D1, D2, D3 light emitting elements, R1a, R1b, R1c, R2a, R2b, R2c, R3a, R3b, R3c, R4a, R4b, R4c, R5a, R5b, R5c, R6a, R6b, R6c resistor elements, T1a, T1b, T1c, T2a, T2b, T2c, T3a, T3b, T3c transistors.

Claims

1. a plurality of detection circuit units provided for the plurality of light emitting elements, each detecting a voltage across the corresponding light emitting element; outputs of the plurality of detection circuit units are connected to a single output terminal; A different signal is output from the output terminal when a failure occurs in at least one of the plurality of light-emitting elements and when a failure does not occur in any of the plurality of light-emitting elements. A fault detection circuit comprising:

2. The plurality of light-emitting elements are connected in series, each of the plurality of detection circuit units includes at least an output-side switching element that outputs a high-level or low-level signal depending on whether or not there is a voltage across the light-emitting element; outputs of the plurality of output-side switching elements are connected to one of the output terminals, outputting a low-level signal from the output terminal when a failure occurs in at least one of the plurality of light-emitting elements; When none of the plurality of light emitting elements is faulty, high level and low level signals are alternately output from the output terminal.

2. The fault detection circuit according to claim 1.

3. each of the plurality of detection circuit units includes a first resistance element, a second resistance element, a third resistance element, a fourth resistance element, a fifth resistance element, a sixth resistance element, a P-channel field effect transistor, a first N-channel field effect transistor, and a second N-channel field effect transistor that is the output-side switching element; a voltage obtained by resistively dividing a voltage across the light emitting element by the first resistor element and the second resistor element is applied between a gate terminal and a source terminal of the P-channel field effect transistor; a voltage obtained by resistively dividing a voltage generated on the drain terminal side of the P-channel field effect transistor by the third resistor element and the fourth resistor element is applied between the gate terminal and the source terminal of the first N-channel field effect transistor, the first N-channel field effect transistor has a gate terminal grounded via the fourth resistor element, a source terminal directly grounded, and a drain terminal connected to a power supply via the fifth resistor element; a voltage generated on the drain terminal side of the first N-channel field effect transistor is applied between the gate terminal and the source terminal of the second N-channel field effect transistor; a drain terminal of the second N-channel field effect transistor is pulled up by the sixth resistor element to a voltage supplied from the power supply; The drain terminals of the second N-channel field effect transistors included in the plurality of detection circuit units are connected to one of the output terminals.

3. The fault detection circuit according to claim 2.

4. The light emitting element is an infrared light emitting diode.

4. The fault detection circuit according to claim 1, wherein the first and second inputs are connected to a first input terminal.

5. an image sensor that captures an image of a subject; a light source for illuminating the subject, the light source being a plurality of infrared light emitting diodes connected in series; a drive circuit that supplies a current to the light-emitting element to cause the light-emitting element to emit light; The fault detection circuit according to any one of claims 1 to 3. An imaging device characterized by:

Images