Protective devices

Abstract

To reduce cost and prevent a load to which power is supplied from being broken by a negative surge due to counter electromotive force of an inductive load.SOLUTION: A protection device includes a switch control unit that controls a switch that is turned on or off in response to a pulse signal input from a drive circuit, supplies power from a power supply to an inductive load when the switch is on, and cuts off power supply from the power supply to the inductive load when the switch is off. The switch control unit causes the drive circuit to output a signal so that the switch is turned off after causing the drive circuit to output a pulse signal so that the switch repeatedly turns on and off in response to a shutdown instruction from a host device.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] An example of an invention for protecting a switching element that supplies power to an inductive load is a protection device disclosed in Patent Document 1. When the current flowing to the inductive load exceeds an overcurrent detection threshold due to, for example, the occurrence of a short circuit, this protection device outputs a PWM (Pulse Width Modulation) signal to the gate of a FET (Field Effect Transistor), which serves as a semiconductor switch that supplies power to the inductive load, so that the duty ratio gradually decreases, and finally the duty ratio of the PWM signal becomes 0. This suppresses fluctuations in the current flowing to the load, preventing damage to the FET. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-90363 Summary of the Invention [Problem to be solved by the invention]

[0004] In a circuit that supplies power to an inductive load, when the semiconductor switch is turned off to stop the power supply, a negative surge occurs downstream of the semiconductor switch due to the back electromotive force of the inductive load. The protection device disclosed in Patent Document 1 provides a clamp diode in parallel with the inductive load downstream of the semiconductor switch to deal with such a negative surge, but providing the clamp diode increases costs.

[0005] The present invention has been made in consideration of the above, and aims to provide a technology that reduces costs and prevents a load supplied with power from a power source from being damaged by a negative surge caused by the back electromotive force of an inductive load. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, a protection device according to one embodiment of the present invention has a switch control unit that controls a switch that turns on or off in response to a pulse signal input from a drive circuit, supplies power from a power source to an inductive load when on, and cuts off the power supply from the power source to the inductive load when off, and in response to a cut-off instruction from a higher-level device, the switch control unit causes the drive circuit to output a pulse signal so that the switch repeatedly turns on and off, and then causes the drive circuit to output a signal that turns the switch off.

[0007] A protection device according to one aspect of the present invention includes an acquisition unit that acquires a voltage value from a voltage measurement unit that measures the voltage value between the switch and the inductive load, and the switch control unit changes the timing of outputting the pulse signal based on the voltage value acquired by the acquisition unit.

[0008] In a protection device according to one embodiment of the present invention, the acquisition unit acquires a voltage value of a voltage applied to a resistor arranged in series with the switch, and includes a calculation unit that calculates a current value of a current flowing from the switch to the inductive load based on the voltage acquired by the acquisition unit, and the switch control unit causes the drive circuit to output a PWM signal as the pulse signal, and changes the off time of the PWM signal based on the current value calculated by the calculation unit when the PWM signal is being output.

[0009] In a protection device according to one aspect of the present invention, the calculation unit calculates a time constant of the current flowing to the load based on the calculated current value, and the switch control unit changes the off time of the PWM signal based on the time constant.

[0010] In a protection device according to one aspect of the present invention, the calculation unit calculates a time constant of the current flowing to the load based on the inductance of the load, the resistance of the load, and the capacitance of the switch, and the switch control unit changes the off time of the PWM signal based on the time constant.

[0011] In a protection device according to one aspect of the present invention, the calculation unit calculates an inductance value of the inductive load based on the current value and the voltage value, calculates the amount of energy of the inductive load based on the inductance value, and stops output of the PWM signal based on the amount of energy.

[0012] In the protection device according to one aspect of the present invention, the current value is the maximum value during the off time of the PWM signal.

[0013] In a protection device according to one aspect of the present invention, the calculation unit calculates the amount of energy in the capacitive component of the switch from the voltage value at the falling edge of the PWM signal, and stops the output of the PWM signal based on the total amount of energy of the calculated amount of energy and the amount of energy in the inductive load.

[0014] In the protection device according to one aspect of the present invention, the calculation unit calculates a charging voltage of a capacitance component of the switch based on the amount of energy, and stops output of the PWM signal based on the charging voltage. [Effects of the Invention]

[0015] The present invention has the effect of reducing costs and preventing a load to which power is supplied from being damaged by a negative surge caused by a back electromotive force of an inductive load. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a block diagram showing the configuration of a protection device according to a first embodiment. [Figure 2]FIG. 2 is a graph showing an example of a change in voltage applied to a semiconductor switch, a change in voltage applied to a load, and a change in current flowing through the load. [Figure 3] FIG. 3 is a block diagram showing the configuration of a protection device according to the second embodiment. [Figure 4] FIG. 4 is a graph showing an example of a change in voltage applied to a load and a change in current flowing through the load. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below. In addition, in the description of the drawings, the same or corresponding elements are appropriately designated by the same reference numerals.

[0018] [First embodiment] FIG. 1 is a block diagram showing the configuration of a protection device according to a first embodiment of the present invention. The power source 2 is, for example, a storage battery mounted on a vehicle. Power supplied from the power source 2 is supplied to a load 3 via a semiconductor switch 4. The semiconductor switch 4 is, for example, a switch including an FET 41 and is connected to the power source 2. The semiconductor switch 4 is turned on or off by a signal output from a drive circuit 5, and outputs or cuts off the power supplied from the power source 2. The drive circuit 5 is a well-known circuit that drives the FET 41 included in the semiconductor switch 4 and outputs a signal that turns the semiconductor switch 4 on or off in response to control from a control unit 10. The load 3 is an inductive load in the vehicle that is driven by power supplied from the power source 2 and is a device that includes a built-in coil. The load 3 is connected to ground GND. The protection device 1A is a device for suppressing negative surges caused by back electromotive force of the load 3 that includes a coil, and is mounted on the vehicle.

[0019] The protection device 1A has a control unit 10 and a first voltage measurement unit 11A. The first voltage measurement unit 11A has a circuit for measuring voltage, and measures the voltage value between the semiconductor switch 4 and the load 3. The voltage value measured by the first voltage measurement unit 11A is output to the control unit 10.

[0020] The control unit 10 includes a processor, a storage unit, and a communication unit that perform various arithmetic operations to control the operation of the protection device 1A in order to realize the function of suppressing negative surges caused by an inductive load. The processor includes, for example, a central processing unit (CPU), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a digital signal processor (DSP), a graphics processing unit (GPU), or other processors.

[0021] The storage unit includes, for example, a ROM (Read Only Memory) that stores various programs and data used by the processor to perform arithmetic processing. The storage unit also includes, for example, a RAM (Random Access Memory) that is used to store a workspace for the processor when performing arithmetic processing and the results of the processor's arithmetic processing. The functions of the control unit 10 are realized as functional units by the processor reading and executing various programs from the storage unit. For example, the switch control unit 102 and the acquisition unit 101 are realized by the processor reading and executing various programs from the storage unit. The switch control unit 102 controls the drive circuit 5 to output a pulse signal from the drive circuit 5 and control the on / off of the semiconductor switch 4. The acquisition unit 101 acquires the voltage value measured by the first voltage measurement unit 11A.

[0022] The communication unit includes a communication module that communicates with an ECU (Electronic Control Unit), which is a higher-level device not shown, and receives instructions and information from the higher-level device.

[0023] Next, an example of the operation of the protection device 1A will be described. When the control unit 10 receives an instruction from a higher-level device to start supplying power to the load 3, it controls the drive circuit 5 to turn on the semiconductor switch 4. In response to the control by the control unit 10, the drive circuit 5 outputs an ON signal to turn on the semiconductor switch 4. The semiconductor switch 4 is turned on by the ON signal from the drive circuit 5, and supplies power from the power source 2 to the load 3. The load 3 is driven by the power supplied from the power source 2 via the semiconductor switch 4.

[0024] When the control unit 10 receives an instruction from a higher-level device to stop the power supply to the load 3, it controls the drive circuit 5 so as to reduce the voltage applied from the semiconductor switch 4 to the load 3. The drive circuit 5 outputs a pulse signal in response to the control from the control unit 10.

[0025] FIG. 2(a) is an example of a graph showing the gate voltage of the FET of the semiconductor switch 4, FIG. 2(b) is an example of a graph showing the source voltage of the FET of the semiconductor switch 4, and FIG. 2(c) is an example of a graph showing the time change of the current flowing through the load 3. At time t1, the drive circuit 5 is controlled to turn off the gate voltage of the FET 41 in response to a stop command, and the source voltage of the FET 41 begins to decrease. The control unit 10 monitors the voltage value acquired from the first voltage measurement unit 11A, i.e., the voltage value of the source voltage of the FET 41. The control unit 10 controls the drive circuit 5 so that a pulse signal Pu is input to the gate of the FET 41 at a timing when the acquired voltage value does not fall below a predetermined lower limit voltage. When the pulse signal Pu is input to the gate of the FET 41, the source voltage of the FET 41 increases at the timing when the pulse signal Pu is input.

[0026] The time for which the pulse signal Pu turns on the gate of the FET 41, i.e., the high-level time of the pulse signal, is preferably the shortest time for turning on the semiconductor switch 4. Furthermore, the timing for outputting the pulse signal Pu is preferably the longest time for which the source voltage of the FET 41 does not fall below a predetermined lower limit voltage. For example, the source voltage Voff shown in FIG. 2(b) at the falling edge of the pulse signal Pu and the source voltage Voffhalf after a predetermined time Toffhalf shown in FIG. 2(b) has elapsed from the falling edge of the pulse signal may be used to calculate the time Toff shown in FIG. 2(b) at which the lower limit voltage Vomin shown in FIG. 2(b) is reached. The next pulse signal Pu may be output when the time Toff has elapsed since the falling edge of the pulse signal Pu. The lower limit voltage may be, for example, a voltage limited by a conventional clamp diode.

[0027] When the output of the pulse signal Pu ends, the source voltage of the FET 41 drops again. After the pulse signal Pu is output, the control unit 10 repeats the output of the pulse signal so that the source voltage of the FET 41 does not fall below the lower limit voltage. When the output of the pulse signal Pu is repeated under the control of the control unit 10, the current flowing through the load 3 decreases as shown in FIG. 2, and the inductive energy of the load 3 decreases.

[0028] For example, when a predetermined time has elapsed, the control unit 10 controls the drive circuit 5 to stop outputting the pulse signal Pu. This time is, for example, the timing when the current flowing through the load 3 becomes equal to or less than a predetermined threshold. When the current flowing through the load 3 decreases, the inductive energy of the load 3 is reduced, so even if the output of the pulse signal is stopped and the semiconductor switch 4 is turned off, the occurrence of a negative surge is suppressed.

[0029] A well-known countermeasure against negative surges is to provide a diode between the semiconductor switch 4 and ground GND, which absorbs the energy of the back electromotive force and suppresses the negative surge. However, if the power of the negative surge is large, a diode with a large capacity is required, which increases costs. On the other hand, according to this embodiment, it is possible to suppress the occurrence of negative surges without using a diode to suppress the occurrence of negative surges, and to prevent damage to the load to which power is supplied from the semiconductor switch 4.

[0030] [Second embodiment] 3 is a diagram showing the configuration of a protection device according to a second embodiment of the present invention. The protection device 1B according to the second embodiment differs from the protection device 1A in that it includes a second voltage measurement unit 11B. Furthermore, when using the protection device 1B, a resistor 6 is provided in series between the semiconductor switch 4 and the load 3.

[0031] Resistor 6 has one end connected to semiconductor switch 4 and the other end connected to load 3, and is connected in series with semiconductor switch 4 and load 3. Resistor 6 is a so-called shunt resistor used to measure the current flowing from semiconductor switch 4 to load 3. First voltage measuring unit 11A is connected to one end of resistor 6 and measures the voltage value of the voltage on one end of resistor 6. Second voltage measuring unit 11B is connected to the other end of resistor 6 and measures the voltage value of the voltage on the other end of resistor 6.

[0032] In the control unit 10 of the protection device 10B, a processor reads and executes various programs from a storage unit, thereby realizing a switch control unit 102, an acquisition unit 101, and a calculation unit 103. The switch control unit 102 causes the drive circuit 5 to output a PWM signal. The acquisition 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 calculation unit 103 calculates the current value of the current flowing through the resistor 6, i.e., the current value of the current flowing from the semiconductor switch 4 to the load 3, based on the voltage value acquired by the acquisition unit 101 from the first voltage measurement unit 11A and the voltage value acquired by the acquisition unit 101 from the second voltage measurement unit 11B, and the resistance value of the resistor 6 previously stored in the storage unit. The calculation unit 103 also sets the PWM signal to be output from the drive circuit 5 using the calculated current value.

[0033] When the control unit 10 receives an instruction from a higher-level device to stop the power supply to the load 3, it controls the drive circuit 5 to output a PWM signal. The drive circuit 5 outputs the PWM signal in accordance with the control by the control unit 10.

[0034] The following describes an example of setting the time Ton, which is the high-level duration of the PWM signal output by the drive circuit 5, the off-time Toff, which is the low-level duration of the PWM signal, and the period of the PWM signal. The setting conditions are: capacitance C across FET 41 = 1 μF, ESR of the capacitance component across FET 41 = 5 mΩ, on-resistance Ron of FET 41 = 1 mΩ, inductance L of load 3 = 0.29 mH, maximum allowable current Imax = 40 A, load current value I(t) calculated by calculation unit 103, maximum power supply voltage Vbmax = 16 V, and power supply voltage Vb = 12 V.

[0035] First, the calculation unit 103 sets the period To of the first PWM signal using equation (1). Under the above conditions, equation (1) determines that To<0.4 μs.

[0036]

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[0037] Next, the calculation unit 103 sets Tonmin, which is the minimum time of the time Ton, using equation (2). This Tonmin is the time it takes for the voltage across the FET 41 to discharge and return to 0 V, and is determined based on the time constants of C and Ron. Under the above conditions, Tonmin = 18 ns.

[0038]

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[0039] Next, the calculation unit 103 sets Toffmax, which is the upper limit time of the off time Toff. Under the above conditions, when the predetermined lower limit voltages Vomin=0V and Voff=8V, for example, Toffmax=0.4 μs. Note that Voff is the voltage measured by the first voltage measurement unit 11A immediately after the PWM signal changes from on to off. Note that the lower limit voltage may be set based on the withstand voltage of the FET 41 or the withstand voltage of the load 3.

[0040]

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[0041] Next, the calculation unit 103 sets T, which is the period of the PWM signal, according to equation (4) using the load current value I(t) that flows through the resistor 6 when it is turned on by the PWM signal.

[0042]

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[0043] Next, the calculation unit 103 calculates the resonance period Tlc generated by the inductance L of the load 3 and the capacitance C across the FET 41 using equation (5).

[0044]

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[0045] When Toffmax becomes longer than 1 / 2 of Tlc, the switch control unit 102 stops outputting the PWM signal.

[0046] By setting the PWM signal in this way and lengthening the PWM signal period, the current supplied to the load 3 decreases, reducing the inductive energy of the load 3. Then, when Toffmax becomes longer than 1 / 2 Tlc and the output of the PWM signal is stopped, the inductive energy of the load 3 has decreased even though the output of the PWM signal has been stopped, so the occurrence of a negative surge can be suppressed without using a clamp diode.

[0047] [Variations] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be implemented in various other forms. For example, the above-described embodiments may be modified as follows to implement the present invention. The above-described embodiments and the following modifications may be combined with each other. The present invention also includes configurations in which the components of the above-described embodiments and modifications are appropriately combined. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-described embodiments and modifications, and various modifications are possible.

[0048] In the above-described embodiment, the time constant may be calculated using di / dt from the change (di) in the current flowing to the load 3 per predetermined time (dt), and the duty of the PWM signal may be adjusted by adjusting the off time of the PWM signal so that the voltage value measured by the second voltage measurement unit 11B does not fall below the lower limit voltage. Specifically, the calculation unit 103 sets the target current for ideal interruption using equation (6), calculates the initial duty of the PWM signal using equation (7), and calculates the dynamic duty of the PWM signal using equation (8). Note that Do in equations (7) and (8) is calculated using equation (9).

[0049]

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[0050]

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[0051]

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[0052]

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[0053] The calculation unit 103 measures the time constant τ from the calculated current value of the current flowing to the load 3, and adjusts the duty of the PWM signal by adjusting the off time Toff with Toffmax as the upper limit so as to approach the target time constant based on the time constant τo of the target current.

[0054] The calculation unit 103 may set the duty by setting the inductance value of the load 3 to L, the resistance value of the load 3 to R, and setting τ in the above-mentioned equation (8) as τ=L / R.

[0055] In the configuration of the protection device 1B, the amount of energy of the load 3 may be calculated based on the calculated current value, and the calculated amount of energy may be used to stop the output of the PWM signal. Specifically, the calculation unit 103 calculates the inductance value L of the load 3 based on equation (10), where L is the inductance value of the load 3, V is the voltage measured by the second voltage measurement unit 11B, dt is the predetermined time, and di is the amount of change in the current value that has changed during dt.

[0056]

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[0057] Next, the calculation unit 103 calculates W, which is the amount of energy in the inductive load, based on the calculated L and the calculated current value, using equation (11).

[0058]

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[0059] For example, when the calculated amount of energy W becomes equal to or less than a predetermined threshold, the control unit 10 stops outputting the PWM signal. This threshold may be the avalanche resistance of the FET 41, for example.

[0060] In the present invention, since the current flowing through the load 3 increases or decreases during the off time of the PWM signal due to the action of the capacitor of the semiconductor switch 4, the calculation unit 103 may calculate the maximum value during the off time of the PWM signal when calculating the current value. In this configuration, the output of the PWM signal may be stopped when the calculated current value becomes equal to or less than a predetermined threshold value.

[0061] In addition, in a configuration in which the amount of energy in the load 3 is calculated, the amount of energy in the capacitor of the semiconductor switch 4 may be calculated from the voltage immediately after the FET 41 is turned off, and the calculated amount of energy may also be used to stop the output of the PWM signal.

[0062] 4 is a graph showing an example of the change in the voltage value measured by the first voltage measurement unit 11A and the current value calculated by the calculation unit 103, where the curved line represents the current value. The calculation unit 103 calculates L, which is the inductance value of the load 3, using equation (10) from the change in the current value after the PWM signal enters the off period, and calculates the amount of energy of the load 3 using equation (11) from the calculated L and the current value Ioff calculated immediately after the PWM signal enters the off period, i.e., the current value calculated at the falling edge of the PWM signal. The calculation unit 103 also calculates the amount of energy of the capacitor of the semiconductor switch 4 using equation (12) based on the voltage value Voff measured by the first voltage measurement unit 11A immediately after the PWM signal enters the off period, and may stop outputting the PWM signal when the sum of the energy amount W of the load 3 and the energy amount Wc of the capacitor is equal to or less than a predetermined threshold.

[0063]

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[0064] In the present invention, the charging voltage Vc of the capacitor of the semiconductor switch 4 is calculated by equation (13) from the amount of energy of the load 3 calculated by equation (11), and when the calculated charging voltage Vc satisfies the relationship of equation (14), the output of the PWM signal may be stopped.

[0065]

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[0066]

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[0067] In the present invention, the protection device 1A and the protection device 1B may be configured to include a drive circuit 5. Furthermore, in the protection device 1B, the first voltage measuring unit 11A and the second voltage measuring unit 11B may be provided externally to the protection device 1B, and the protection device 1B may acquire voltage values ​​from the externally provided first voltage measuring unit 11A and second voltage measuring unit 11B.

[0068] In the above-described embodiment, the case where the protection devices 1A and 1B are mounted on a vehicle has been described, but the installation of the protection devices 1A and 1B is not limited to a vehicle, and they can be applied to a device that drives an inductive load. [Explanation of symbols]

[0069] 1A, 1B, Protective device 2 Power supply 3. Load 4. Solid-state switches 5. Drive circuit 6 resistor 10 Control Unit 11A 1st voltage measurement section 11B Second voltage measurement unit 101 Acquisition Department 102 Switch control section 103 Calculation Unit GND Ground

Claims

1. a switch control unit that controls a switch that is turned on or off in response to a pulse signal input from a drive circuit, and that supplies power from a power source to an inductive load when the switch is on, and cuts off the power supply to the inductive load when the switch is off; an acquisition unit that acquires a voltage value between the switch and the inductive load from a voltage measurement unit that measures the voltage value; a calculation unit that calculates a current value of a current flowing from the switch to the inductive load based on the voltage acquired by the acquisition unit; and the acquisition unit acquires a voltage value of a voltage applied to a resistor connected in series to the switch, The switch control unit, in response to a cut-off instruction from a higher-level device, causes the drive circuit to output a PWM signal as a pulse signal so that the switch repeatedly turns on and off, and then causes the drive circuit to output a signal that turns off the switch, changes the output timing of the PWM signal based on the voltage value acquired by the acquisition unit, and changes the off time of the PWM signal based on the current value calculated by the calculation unit when the PWM signal is being output. Protective device.

2. the calculation unit calculates a time constant of a current flowing to the load based on the calculated current value; The switch control unit changes the off time of the PWM signal based on the time constant. The protection device of claim 1 .

3. the calculation unit calculates a time constant of a current flowing to the load based on an inductance of the load, a resistance of the load, and a capacitance of the switch; The switch control unit changes the off time of the PWM signal based on the time constant. The protection device of claim 1 .

4. The calculation unit calculates an inductance value of the inductive load based on the current value and the voltage value, calculates an amount of energy of the inductive load based on the inductance value, and stops output of the PWM signal based on the amount of energy. The protection device of claim 1 .

5. The current value is the maximum value during the off time of the PWM signal.

5. The protection device of claim 4.

6. The calculation unit calculates the amount of energy of the capacitance component of the switch from the voltage value at the falling edge of the PWM signal, and stops output of the PWM signal based on the total amount of energy of the calculated amount of energy and the amount of energy of the inductive load.

5. The protection device of claim 4.

7. The calculation unit calculates a charging voltage of a capacitance component of the switch based on the amount of energy, and stops output of the PWM signal based on the charging voltage.

5. The protection device of claim 4.

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