Protective devices

Abstract

To reduce a cost, and prevent occurrence of a short-circuit.SOLUTION: A protection device includes a switch control unit that controls a switch which is turned on / off in response to an inputted pulse signal, and supplies power from a power source to a load when the switch is on and shuts off the power supply to the load when the switch is off, and a computation unit that obtains a voltage value of voltage between the power source and the switch measured within a prescribed time period since an input of the pulse signal to the switch, and a voltage value of voltage between the switch and the load, from a voltage measurement unit that measures the voltage values, and calculates a resistance value at a stage subsequent to the switch on the basis of the resistance value of the switch and the obtained voltage values. When the switch is on in response to the pulse signal, the load is not in operation. The switch control unit turns off the switch when the resistance value calculated by the computation unit is less than a threshold.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a protection device.

Background Art

[0002] As an invention for preventing overcurrent from flowing from a power source to a load, for example, there is a switch device disclosed in Patent Document 1. This switch device has a switch circuit and a connector connected to a load. The switch circuit has a main switch provided in a first current path from a DC power source to the connector and a sub-switch provided in a second current path from the DC power source to the connector. Further, the switch circuit has a resistor in parallel with the main switch and the sub-switch. In the switch circuit, the resistance value when the sub-switch is on is larger than the resistance value when the main switch is on. The switch device acquires the voltage of a connection node on the downstream side of the main switch and the sub-switch in a state where the main switch is off and the sub-switch is on. Then, the switch circuit determines based on the acquired voltage whether the current flowing through the main switch when the main switch is switched on is less than a threshold value. This threshold value is less than the voltage of the DC power source and is a voltage exceeding the voltage obtained by dividing the voltage of the DC power source by the resistor and the load. The switch device maintains the main switch off when the acquired voltage is equal to or higher than this threshold value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the case of the switch device disclosed in Patent Document 1, an additional resistor is required in parallel with the main switch and the sub-switch, increasing the number of components and thus the cost.

[0005] The present invention has been made in view of the above, and aims to provide a technology that reduces costs and prevents short circuits from occurring. [Means for solving the problem]

[0006] To solve the above-mentioned problems and achieve the objective, a protective device according to one aspect of the present invention includes a switch control unit that controls a switch which turns on or off in response to an input pulse signal, supplies power from a power source to a load when on, and cuts off the power supply from the power source to the load when off; and a calculation unit that obtains the voltage value of the voltage between the power source and the switch, measured within a predetermined time after the pulse signal is input to the switch, and the voltage value of the voltage between the switch and the load from a voltage measuring unit that measures the said voltage value, and calculates the resistance value of the downstream stage of the switch based on the resistance value of the switch and the acquired voltage value, wherein the time during which the switch turns on in response to the pulse signal is the time during which the load is not operating, and the switch control unit turns off the switch if the resistance value calculated by the calculation unit is less than a threshold.

[0007] In a protective device according to one aspect of the present invention, the pulse signal is a PWM signal with a duty cycle in which the load does not operate, and the calculation unit acquires the output voltage of a low-pass filter that smooths the voltage change between the switch and the load as the voltage value of the voltage between the switch and the load.

[0008] In a protective device according to one aspect of the present invention, the calculation unit calculates the potential difference between the ground potential of the load and the ground potential of the voltage measuring unit based on the acquired voltage value and the duty cycle, and calculates the resistance value of the stage downstream of the switch based on the calculated potential difference, the voltage value acquired by the calculation unit, and the resistance value of the switch.

[0009] In a protective device according to one aspect of the present invention, the calculation unit calculates the potential difference based on the voltage value obtained when the PWM signal has a first duty cycle, the voltage value obtained when the PWM signal has a second duty cycle, the first duty cycle, and the second duty cycle.

[0010] In a protective device according to one aspect of the present invention, the switch control unit controls a first sub-switch provided in parallel with the switch and a second sub-switch provided in parallel with the load. The calculation unit calculates the potential difference between the ground potential of the load and the ground potential of the voltage measuring unit based on the voltage value of the voltage applied to the load acquired when the first sub-switch is ON and the switch and the second sub-switch are OFF, the voltage value of the voltage applied to the load acquired when the first sub-switch and the second sub-switch are ON and the switch is OFF, and the current value of the current flowing through the second sub-switch. The calculation unit then calculates the resistance value of the stage downstream of the switch based on the calculated potential difference, the voltage value acquired by the calculation unit, and the resistance value of the switch.

[0011] In a protective device according to one aspect of the present invention, the voltage value acquired by the calculation unit is the voltage value measured by the voltage measurement unit during the falling edge of the pulse signal.

[0012] In a protective device according to one aspect of the present invention, the switch is an FET, the voltage value applied to the gate of the FET when the switch is turned on by the pulse signal is a voltage value obtained by adding a predetermined voltage value to the gate threshold value of the FET, and the switch control unit turns off the switch if the voltage value of the voltage between the switch and the load obtained when the switch is turned on by the pulse signal is less than the predetermined voltage value. [Effects of the Invention]

[0013] According to the present invention, it is possible to reduce costs and prevent short circuits from occurring. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a block diagram showing the configuration according to the first embodiment. [Figure 2] Figure 2 shows an example of a signal waveform related to the control of the first embodiment. [Figure 3] Figure 3 is a block diagram showing the configuration according to the second embodiment. [Figure 4] Figure 4 is a graph showing the relationship between the voltage applied to the load and the duty cycle of the PWM signal input to the semiconductor switch. [Figure 5] Figure 5 is a block diagram showing the configuration according to the third embodiment. [Figure 6] Figure 6 shows an example of a signal waveform related to control in the third embodiment. [Figure 7] Figure 7 shows an example of a signal waveform related to control in the third embodiment. [Figure 8] Figure 8 is a block diagram showing the configuration according to the fourth embodiment. [Modes for carrying out the invention]

[0015] Embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the embodiments described below. Furthermore, in the drawings, the same or corresponding elements are denoted by the same reference numerals as appropriate.

[0016] [First Embodiment] FIG. 1 is a block diagram showing the configuration of a protection device 1A according to the first embodiment of the present invention. The power supply 2 is, for example, a storage battery mounted on a vehicle. The power supplied by the power supply 2 is supplied from the positive electrode of the power supply 2 to the load 3 via the semiconductor switch 4. The semiconductor switch 4 is a switch including, for example, a FET (Field effect transistor) and is connected to the positive electrode of the power supply 2. The semiconductor switch 4 is turned on or off by a signal output from the protection device 1A, and outputs and cuts off the power supplied from the power supply 2. The load 3 is an electrical component driven by the power supplied from the semiconductor switch 4 in the vehicle. The load 3 is connected to the negative electrode of the power supply 2 via the ground line G. The protection device 1A is a device that prevents short circuits and is mounted on a vehicle.

[0017] The protection device 1A includes a control unit 10, a first voltage measurement unit 11A, and a second voltage measurement unit 11B. The first voltage measurement unit 11A has a circuit for measuring voltage and is connected between the semiconductor switch 4 and the power supply 2 and to the ground line G. The first voltage measurement unit 11A measures the voltage value of the voltage between the semiconductor switch 4 and the power supply 2. The voltage value measured by the first voltage measurement unit 11A is output to the control unit 10. The second voltage measurement unit 11B has a circuit for measuring voltage and is connected between the semiconductor switch 4 and the load 3 and to the ground line G. The second voltage measurement unit 11B measures the voltage value of the voltage between the semiconductor switch 4 and the load 3. The voltage value measured by the second voltage measurement unit 11B is output to the control unit 10.

[0018] The control unit 10 includes an arithmetic unit 101 and a switch control unit 102 to realize the function of preventing the occurrence of a short circuit. The arithmetic unit 101 acquires the voltage value measured by the first voltage measurement unit 11A and the voltage value measured by the second voltage measurement unit 11B. The arithmetic unit 101 calculates the resistance value of the load 3 based on the acquired voltage value and the resistance value of the semiconductor switch 4 when the semiconductor switch 4 is turned on. Also, the arithmetic unit 101 acquires an operation signal from an upper device (not shown), namely an ECU (Electronic Control Unit). The operation signal is a signal indicating whether to turn on or off the semiconductor switch 4. The arithmetic unit 101 outputs an output control signal Sa and a pulse signal Sb to the switch control unit 102 according to the calculation result and the operation signal. The switch control unit 102 acquires an operation signal from the ECU. The switch control unit 102 outputs a switch control signal Sc for turning on or off the semiconductor switch 4 according to the operation signal, the output control signal Sa, and the pulse signal Sb.

[0019] Note that the control unit 10 may be configured to include a processor that performs various arithmetic processes and a storage unit. The processor includes, for example, processors such as a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), a DSP (Digital Signal Processor), and a GPU (Graphics Processing Unit). The storage unit stores various programs and data used for the processor to perform arithmetic processes, for example, and includes a ROM (Read Only Memory). Also, the storage unit is used to store, for example, a work space when the processor performs arithmetic processes and the results of the processor's arithmetic processes, and includes a RAM (Random Access Memory). The functions of the control unit 10 may be realized as functional units by the processor reading and executing various programs from the storage unit.

[0020] Next, an example of the operation of the protective device 1A will be explained using Figure 2. Figure 2 is a diagram showing an example of the waveform of a control signal. When the ECU supplies power to the load 3, it outputs a high-level operating signal. This operating signal is supplied to the calculation unit 101 and the switch control unit 102. When the level of the operating signal changes from low level to high level, the calculation unit 101 outputs a low-level output control signal Sa and a pulse signal Sb that turns on the semiconductor switch 4 for a predetermined time. This pulse signal Sb is, for example, a one-shot pulse signal that is high level for a certain period of time. The certain period of time during which this pulse signal is high level is set to a time during which the semiconductor switch 4 will not be damaged even if a short circuit occurs.

[0021] The switch control unit 102 outputs a switch control signal Sc, which is a one-shot pulse signal that is high level for a certain period of time in response to the pulse signal Sb. The semiconductor switch 4 turns on when the switch control signal Sc is high level. When the semiconductor switch 4 is turned on, current flows to the load 3 through the semiconductor switch 4. The calculation unit 101 acquires the voltage value measured by the first voltage measurement unit 11A and the voltage value measured by the second voltage measurement unit 11B during the period when the semiconductor switch 4 is turned on by the switch control signal Sc.

[0022] Next, the calculation unit 101 calculates the resistance of the load 3 based on the acquired voltage value and the resistance value of the semiconductor switch 4 when the semiconductor switch 4 is turned on. Specifically, if the resistance of the load 3 is RL, the voltage value acquired from the first voltage measurement unit 11A is Vb, the voltage value acquired from the second voltage measurement unit 11B is VL, and the resistance value of the semiconductor switch 4 when the semiconductor switch 4 is turned on is Ron, the calculation unit 101 calculates RL using equation (1). Note that Ron is set in the calculation unit 101 in advance, for example.

[0023]

number

[0024] The calculation unit 101 outputs a high-level output control signal Sa, as shown in Figure 2, if the calculated RL is greater than or equal to a predetermined threshold. This threshold is, for example, the resistance value of the load 3, which is pre-set in the calculation unit 101. The switch control unit 102 outputs a high-level switch control signal Sc to turn on the semiconductor switch 4 if the operating signal is high level and the output control signal Sa is high level. The semiconductor switch 4 is turned on by this switch control signal Sc. When the semiconductor switch 4 is turned on, current flows to the load 3 through the semiconductor switch 4.

[0025] On the other hand, if the calculated RL is less than a predetermined threshold, the calculation unit 101 outputs information to the ECU indicating that a short circuit has occurred. Since RL will be below the threshold when a short circuit occurs downstream of the semiconductor switch 4, the control unit 10 can detect the short circuit by comparing RL with the threshold. Furthermore, if the calculated RL is less than a predetermined threshold, the calculation unit 101 outputs a low-level output control signal Sa when the operating signal is at a high level. In this case, since the output control signal Sa is at a low level, the switch control unit 102 outputs a switch control signal Sc to turn off the semiconductor switch 4.

[0026] When the ECU stops supplying power to load 3, it outputs a low-level operation signal. This operation signal is supplied to the calculation unit 101 and the switch control unit 102. As shown in Figure 2, when the level of the operation signal changes from high to low, the calculation unit 101 outputs a low-level output control signal Sa. When the switch control unit 102 receives the low-level output control signal Sa, it outputs a low-level switch control signal Sc that turns off the semiconductor switch 4. The semiconductor switch 4 is turned off by this low-level switch control signal Sc. When the semiconductor switch 4 is turned off, no current flows from the semiconductor switch 4 to load 3.

[0027] According to this embodiment, it is possible to detect whether or not a short circuit occurs when supplying power to the load 3 without providing a sub-switch in parallel with the semiconductor switch 4, thereby reducing costs and preventing short circuits. Furthermore, according to this embodiment, the time required to supply current for detection can be reduced compared to a configuration in which the semiconductor switch 4 is kept on and then detected whether or not a short circuit occurs.

[0028] Furthermore, if load 3 has a capacitance component, when the switch control signal Sc falls, the voltage measured by the second voltage measurement unit 11B will transiently decrease. The calculation unit 101 may use the voltage value acquired during the falling edge of the pulse signal as VL and perform the calculation in equation (1).

[0029] [Second Embodiment] Figure 3 is a block diagram showing the configuration according to the second embodiment of the present invention. The second embodiment differs from the first embodiment in that the pulse signal Sb is a PWM signal and a low-pass filter 5 is used. In the following, components that are the same as in the first embodiment are denoted by the same reference numerals and their descriptions are omitted, and the differences from the first embodiment will be described.

[0030] The low-pass filter 5 has its input side connected between the semiconductor switch 4 and the load 3, and its output side connected to the second voltage measuring unit 11B. The second voltage measuring unit 11B measures the voltage value of the output side of the low-pass filter 5.

[0031] When the level of the operating signal supplied from the ECU changes from a low level to a high level, the calculation unit 101 outputs a low-level output control signal Sa and a pulse signal Sb, which is a PWM signal. The duty cycle of this pulse signal Sb is set to a duty cycle in which load 3 does not operate.

[0032] The switch control unit 102 outputs a switch control signal Sc, which is a PWM signal with the same duty cycle as the pulse signal Sb, in response to the pulse signal Sb, which is a PWM signal. This switch control signal Sc causes the semiconductor switch 4 to turn on during periods when the PWM signal is high-level and turn off during periods when the PWM signal is low-level, repeatedly switching on and off. As the semiconductor switch 4 repeatedly switches on and off, the input voltage of the low-pass filter 5 becomes high when the semiconductor switch 4 is on and low when the semiconductor switch 4 is off. The low-pass filter 5 smooths the changes in the input voltage, and the second voltage measurement unit 11B measures the voltage value of the voltage smoothed by the low-pass filter 5.

[0033] The calculation unit 101 acquires the voltage values ​​measured by the first voltage measurement unit 11A and the second voltage measurement unit 11B, and calculates the resistance value of the load 3 based on the acquired voltage values ​​and the resistance value of the semiconductor switch 4 when the semiconductor switch 4 is turned on. Specifically, if the resistance value of the load 3 is RL, the voltage value measured by the first voltage measurement unit 11A is Vb, the voltage value measured by the second voltage measurement unit 11B is VL, and the resistance value of the semiconductor switch 4 when the semiconductor switch 4 is turned on by the PWM signal is Ron_pwm, the calculation unit 101 calculates RL using equation (2). Ron_pwm is a value calculated as Ron / Dn, where Dn is the duty cycle of the PWM signal. VL is the voltage value of the voltage that has been smoothed and saturated by the low-pass filter 5. Ron_pwm is set in advance in the calculation unit 101.

[0034]

number

[0035] The calculation unit 101 outputs a high-level output control signal Sa if RL calculated by equation (2) is equal to or greater than a predetermined threshold. The switch control unit 102 outputs a high-level switch control signal Sc to turn on the semiconductor switch 4 if the operating signal is high level and the output control signal Sa is high level. The semiconductor switch 4 is turned on by this switch control signal Sc. When the semiconductor switch 4 is turned on, current flows to the load 3 through the semiconductor switch 4.

[0036] On the other hand, if the calculation unit 101 finds that RL calculated by equation (2) is less than a predetermined threshold, it outputs information to the ECU indicating that a short circuit has occurred. Since RL will be less than or equal to the threshold if there is a short circuit downstream of the semiconductor switch 4, the control unit 10 can detect the short circuit by comparing RL with the threshold. Furthermore, if the calculated RL is less than a predetermined threshold, the calculation unit 101 outputs a low-level output control signal Sa when the operating signal is at a high level. In this case, since the output control signal Sa is at a low level, the switch control unit 102 outputs a switch control signal Sc to turn off the semiconductor switch 4.

[0037] According to this embodiment, it is possible to detect whether or not a short circuit occurs when supplying power to the load 3 without providing a sub-switch in parallel with the semiconductor switch 4, thereby reducing costs and preventing short circuits. Furthermore, according to this embodiment, compared to a configuration that outputs a one-shot pulse signal, the voltage measured by the second voltage measurement unit 11B is more stable, making it easier to measure VL.

[0038] In a vehicle, the position of load 3 is far from the positions of the first voltage measuring unit 11A and the second voltage measuring unit 11B, which may result in a difference between the ground potential of load 3 and the ground potential of the first voltage measuring unit 11A and the second voltage measuring unit 11B. Since such a potential difference in the ground makes it impossible to accurately calculate RL, the control unit 10 according to the second embodiment may calculate RL taking this potential difference into consideration.

[0039] Specifically, when the calculation unit 101 receives a high-level operating signal from the ECU, it obtains the voltage value measured by the first voltage measurement unit 11A when it outputs a pulse signal Sb with a duty cycle of 100%. In the following description, this voltage value will be referred to as Vb. This voltage value may be stored in advance, or it may be measured by the first voltage measurement unit 11A when no short circuit occurs and stored.

[0040] Next, the calculation unit 101 outputs a pulse signal Sb, which is a PWM signal. The duty cycle of this PWM signal is set to a duty cycle in which load 3 does not operate. In the following explanation, this duty cycle of the PWM signal will be denoted as Dn. The calculation unit 101 obtains the voltage value measured by the second voltage measurement unit 11B when the pulse signal Sb with a duty cycle of Dn is output. The calculation unit 101 denotes this voltage value measured by the second voltage measurement unit 11B, i.e., the voltage value of the output side of the low-pass filter 5, as VLn. Next, the calculation unit 101 calculates Voffset, which is the potential of the ground of load 3, using equation (3). Then, the calculation unit 101 uses the calculated Voffset to calculate RL using equation (4).

[0041]

number

[0042]

number

[0043] The calculation unit 101 outputs a high-level output control signal Sa if the RL calculated by equation (4) is greater than or equal to a predetermined threshold. The switch control unit 102 outputs a high-level switch control signal Sc to turn on the semiconductor switch 4 if the operating signal is high level and the output control signal Sa is high level. The semiconductor switch 4 is turned on by this switch control signal Sc. When the semiconductor switch 4 is turned on, current flows to the load 3 through the semiconductor switch 4.

[0044] On the other hand, if the RL calculated by equation (4) is less than a predetermined threshold, the calculation unit 101 outputs information to the ECU indicating that a short circuit has occurred. Also, if the calculated RL is less than a predetermined threshold, the calculation unit 101 outputs a low-level output control signal Sa when the operating signal is at a high level. In this case, since the output control signal Sa is at a low level, the switch control unit 102 outputs a switch control signal Sc to turn off the semiconductor switch 4.

[0045] Figure 4 is a graph showing the relationship between VLn and Dn when there is a difference between the ground potential of load 3 and the ground potentials of the first voltage measurement unit 11A and the second voltage measurement unit 11B. When there is a difference between the ground potential of load 3 and the ground potentials of the first voltage measurement unit 11A and the second voltage measurement unit 11B, VLn is based on the ground potential of the second voltage measurement unit 11B, so calculating RL using equation (2) will not yield the correct RL. On the other hand, with a configuration in which Voffset is calculated using equations (3) and (4) with Vb when the semiconductor switch 4 is turned on and a PWM signal with a duty cycle of Dn, and RL is calculated using the calculated Voffset, RL can be accurately calculated even when there is a difference between the ground potential of load 3 and the ground potentials of the first voltage measurement unit 11A and the second voltage measurement unit 11B.

[0046] Alternatively, the first duty cycle may be defined as Dn, the second duty cycle as Dn2, and the voltage value measured by the second voltage measuring unit 11B when the duty cycle is Dn2 as VLn2. VLn2 may be used instead of Vb, and the 1 in the denominator of equation (3) may be replaced with Dn2 to calculate Voffset.

[0047] [Third Embodiment] Figure 5 is a block diagram showing the configuration according to the third embodiment of the present invention. In the protective device 1A according to the third embodiment, the configuration for detecting whether or not a short circuit occurs differs from that of the first embodiment. In the following, the same reference numerals are used for components that are the same as in the first embodiment and their descriptions are omitted, and the differences from the first embodiment will be described.

[0048] As shown in Figure 5, in the third embodiment, a resistor 6, a switch 7, an operational amplifier 8, and a clamp power supply 9 are provided outside the protective device 1A. One end of the resistor 6 is connected to the switch control unit 102, and the other end is connected to the gate of the FET of the semiconductor switch 4. One end of the switch 7 is connected to the output terminal of the operational amplifier 8, and the other end is connected between the resistor 6 and the semiconductor switch 4. The switch 7 is turned on or off by a diagnostic signal Sd output from the switch control unit 102. The clamp power supply 9 is a power supply with a predetermined voltage. The non-inverting input terminal of the operational amplifier 8 is connected to the positive terminal of the clamp power supply 9, and the inverting input terminal is connected between the semiconductor switch 4 and the load 3. The output terminal of the operational amplifier 8 is connected to the switch 7.

[0049] Next, an example of the operation of the protective device 1A according to the third embodiment will be explained using Figure 6, specifically an example of operation when no short circuit occurs. Figure 6 is a diagram showing an example of the waveform of a control signal. When the level of the operating signal changes from a low level to a high level, the switch control unit 102 outputs a diagnostic signal Sd that turns on the switch 7 for a predetermined period of time. When the level of the operating signal changes from a low level to a high level, the calculation unit 101 outputs a low-level output control signal Sa and a pulse signal Sb. This pulse signal Sb is, for example, a one-shot pulse signal that is high for a certain period of time. The timing at which this pulse signal Sb becomes high is set to be later than the timing at which the diagnostic signal Sd becomes high. In response to the pulse signal Sb, the switch control unit 102 outputs a switch control signal Sc that turns on the semiconductor switch 4 for a certain period of time.

[0050] When the diagnostic signal Sd turns on switch 7, and the switch control unit 102 outputs a switch control signal Sc to turn on semiconductor switch 4, if the voltage of the clamp power supply 9 is VCL, then if no short circuit occurs, VL = VCL. When the diagnostic signal Sd turns on switch 7, and the switch control unit 102 outputs a switch control signal Sc to turn on semiconductor switch 4, the calculation unit 101 acquires the voltage value measured by the first voltage measurement unit 11A. This voltage value is the gate voltage applied to the gate of the FET of semiconductor switch 4. If Vth is the gate threshold voltage that turns on the FET of semiconductor switch 4, and Vg is the gate voltage of the FET of semiconductor switch 4, then if no short circuit occurs, Vg = VCL + Vth is obtained from the output of the operational amplifier 8.

[0051] If the voltage value acquired by the first voltage measurement unit 11A is VCL + Vth, the calculation unit 101 outputs a high-level output control signal Sa after the diagnostic signal Sd and pulse signal Sb become low levels. If the switch control unit 102 is at a high level and the output control signal Sa is also at a high level, it outputs a switch control signal Sc to turn on the semiconductor switch 4. At this point, since switch 7 is off, this switch control signal Sc applies a voltage to the gate of the FET of the semiconductor switch 4, turning on the FET and the semiconductor switch 4. When the semiconductor switch 4 is turned on, current flows to the load 3 through the semiconductor switch 4.

[0052] Next, regarding the operation example of the protection device 1A according to the third embodiment, an operation example when a short circuit occurs will be described using FIG. 7. FIG. 7 is a diagram showing an example of the waveform of a signal related to control. When the switch 7 is turned on by the diagnostic signal Sd and the switch control signal Sc for turning on the semiconductor switch 4 is output from the switch control unit 102, if the voltage of the clamp power supply 9 is VCL and a short circuit has occurred, VL < VCL. When the switch 7 is turned on by the diagnostic signal Sd and the switch control signal Sc for turning on the semiconductor switch 4 is output from the switch control unit 102, the arithmetic unit 101 acquires the voltage value of the voltage measured by the first voltage measurement unit 11A. This voltage value is the gate voltage applied to the gate of the FET of the semiconductor switch 4. When a short circuit has occurred, Vg represented by the acquired voltage value becomes Vg > VCL + Vth due to the output of the operational amplifier 8.

[0053] When the voltage value acquired by the first voltage measurement unit 11A exceeds VCL + Vth, the arithmetic unit 101 outputs a low-level output control signal Sa after the diagnostic signal Sd and the pulse signal Sb become low level. When the operation signal is high level and the output control signal Sa is low level, the switch control unit 102 outputs a switch control signal Sc for turning off the semiconductor switch 4. Here, since the switch 7 is off, a voltage for turning off the FET is applied to the gate of the FET of the semiconductor switch 4 by this switch control signal Sc, and the semiconductor switch 4 turns off. When the semiconductor switch 4 turns on, the current does not flow from the semiconductor switch 4 to the load 3.

[0054] Note that the arithmetic unit 101 may acquire the voltage value of the voltage measured by the second voltage measurement unit 11B after the switch 7 is turned on by the diagnostic signal Sd and the switch control signal Sc for turning on the semiconductor switch 4 is output from the switch control unit 102. In this case, when the acquired voltage value is less than VCL, the arithmetic unit 101 may output a low-level output control signal Sa after the diagnostic signal Sd and the pulse signal Sb become low level.

[0055] [Fourth Embodiment] Figure 8 is a block diagram showing the configuration according to the fourth embodiment of the present invention. The semiconductor switches 4a, 4b, and 4c are switches including an FET 41 and are connected to the control unit 10. In semiconductor switch 4a, the drain of the FET 41a is connected to the power supply 2, the gate is connected to the control unit 10, and the source is connected to the current measuring unit 12. In semiconductor switch 4b, the drain of the FET 41b is connected to the power supply 2, the gate is connected to the control unit 10, and the source is connected to resistor R1. Resistor R1 is connected to the current measuring unit 12.

[0056] The protection device 1B includes a control unit 10, a current measuring unit 12, and a voltage measuring unit 13. The current measuring unit 12 has a circuit for measuring current and is connected to the source of the FET 41a of the semiconductor switch 4a and to the load 3. The current measuring unit 12 measures the current value of the current output from the semiconductor switch 4a and flowing to the load 3. The current value measured by the current measuring unit 12 is output to the control unit 10. The voltage measuring unit 13 has a circuit for measuring voltage and measures the voltage value of the voltage between the current measuring unit 12 and the load 3. The voltage value measured by the voltage measuring unit 13 is output to the control unit 10. In the semiconductor switch 4c, one end of resistor R2 is connected between the current measuring unit 12 and the load 3, and the other end is connected to the drain of the FET 41c of the semiconductor switch 4c. In addition, the gate of the FET 41 of the semiconductor switch 4c is connected to the control unit 10, and the source is connected to ground GND.

[0057] In the second embodiment, when there was a difference in the potential of the ground (GND), the potential difference was determined using a PWM signal. However, in the fourth embodiment, the potential difference is determined by another method. In the following description, Ra is the resistance of semiconductor switch 4a when FET 41a is ON, Rb is the resistance of semiconductor switch 4b when FET 41b is ON, and Rc is the resistance of semiconductor switch 4c when FET 41c is ON. Also, VI is the voltage applied to semiconductor switches 4a and 4b, VL is the voltage applied to load 3, and Vdiff is the potential difference between the potential at point a and point b on the ground. Furthermore, IL is the current flowing through load 3, Ib is the current flowing through semiconductor switch 4b, and Ic is the current flowing through semiconductor switch 4c.

[0058] In calculating Vdiff, the control unit 10 first outputs a signal to turn off semiconductor switch 4a, a signal to turn on semiconductor switch 4b, and a signal to turn off semiconductor switch 4c. Note that the current flowing to load 3 when semiconductor switch 4b is turned on is the current that does not drive load 3. When semiconductor switch 4b is turned on, the control unit 10 acquires the voltage value measured by the voltage measurement unit 13. If this voltage value is denoted as VO, then VO is expressed by equation (5).

[0059]

number

[0060] Next, the control unit 10 outputs a signal to turn on the semiconductor switch 4c while keeping the semiconductor switch 4b ON, and acquires the current value measured by the current measurement unit 12 and the voltage value measured by the voltage measurement unit 13. This measured current value is Ib, and Ib = Ic + IL. Also, if the voltage value acquired here is VO, then Ic = VO / Rc, IL = VL / RL, and VL = VO - Vdiff. Since Ic and IL can be obtained from these equations, Vdiff can be calculated by combining them with equation (5).

[0061] [Differentiation] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above and can be implemented in various other forms. For example, the present invention may be implemented by modifying the embodiments described above as follows. The embodiments described above and the following modifications may be combined with each other. The present invention is also included in configurations that appropriately combine the components of each embodiment and each modification described above. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, broader embodiments of the present invention are not limited to the embodiments and modifications described above, and various modifications are possible.

[0062] In the present invention, the protective device 1A may have a first voltage measuring unit 11A and a second voltage measuring unit 11B located outside the protective device 1A, and the protective device 1A may acquire voltage values ​​from the first voltage measuring unit 11A and the second voltage measuring unit 11B located outside the protective device 1A.

[0063] In the embodiments described above, the case in which the protective device 1A is mounted on a vehicle was explained, but the protective device 1A is not limited to being mounted on a vehicle and can be applied to devices that drive a load with a semiconductor switch. [Explanation of Symbols]

[0064] 1A, 1B Protective device 2 power supply 3 load 4, 4a, 4b, 4c semiconductor switches 5. Low-pass filter 6 resistor 7 Switches 8 operational amplifiers 9. Clamp power supply 10 Control Unit 11A First Voltage Measurement Section 11B Second Voltage Measurement Section 12 Current measurement section 13 Voltage Measurement Section 41, 41a, 41b, 41c FET 101 Arithmetic section 102 Switch Control Unit G Grand Line GND (Ground) Sa output control signal Sb pulse signal Sc switch control signal Sd diagnostic signal

Claims

1. A switch control unit controls a switch that turns on or off in response to an input pulse signal, supplying power from a power source to a load when on, and cutting off the power supply from the power source to the load when off. A voltage measuring unit obtains the voltage value of a first voltage between the power supply and the switch, and the voltage value of a second voltage between the switch and the load, measured within a predetermined time after the pulse signal is input to the switch, from a voltage measuring unit that measures the voltage values, and calculates the resistance value of the stage downstream of the switch based on the resistance value of the switch and the obtained voltage values ​​of the first and second voltages. It has, The aforementioned power supply has its negative terminal connected to ground. The switch is connected in series between the positive terminal of the power supply and the load, The load is connected in series with respect to the switch and the ground between the switch and the ground. The time during which the switch turns on in response to the pulse signal is the time during which the load is not operating. The switch control unit turns off the switch if the resistance value calculated by the calculation unit is less than a threshold value. Protective device.

2. The pulse signal is a PWM signal with a duty cycle in which the load does not operate. The calculation unit obtains the output voltage of the low-pass filter that smooths the voltage change between the switch and the load as the voltage value of the second voltage between the switch and the load. The low-pass filter is connected between the switch and the load and to the voltage measuring unit. The protective device according to claim 1.

3. The calculation unit calculates the ground potential of the load based on the acquired voltage value of the first voltage, the voltage value of the second voltage, and the duty cycle, and calculates the resistance value of the stage downstream of the switch based on the calculated potential, the voltage value acquired by the calculation unit, and the resistance value of the switch. The protective device according to claim 2.

4. The calculation unit calculates the potential based on the voltage value obtained when the PWM signal has a first duty cycle, the voltage value obtained when the PWM signal has a second duty cycle, the first duty cycle, and the second duty cycle. The protective device according to claim 3.

5. The switch control unit controls a first sub-switch provided in parallel with the switch and a second sub-switch provided in parallel with the load. The calculation unit calculates the potential difference between the ground potential of the load and the ground potential of the voltage measuring unit based on the voltage value of the voltage applied to the load obtained when the first sub-switch is ON and the switch and the second sub-switch are OFF, the voltage value of the voltage applied to the load obtained when the first sub-switch and the second sub-switch are ON and the switch is OFF, and the current value of the current flowing through the second sub-switch. Based on the calculated potential difference, the voltage value obtained by the calculation unit, and the resistance value of the switch, it calculates the resistance value of the stage downstream of the switch. The protective device according to claim 1.

6. The voltage value acquired by the calculation unit is the voltage value measured by the voltage measurement unit during the falling edge of the pulse signal. The protective device according to claim 1.

7. The aforementioned switch is an FET, The voltage value applied to the gate of the FET when the switch is turned on by the pulse signal is the voltage value obtained by adding a predetermined voltage value to the gate threshold value of the FET. The switch control unit turns off the switch if the voltage value of the second voltage between the switch and the load, obtained when the switch is ON by the pulse signal, is less than the predetermined voltage value. The protective device according to claim 1.

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