Load Driver

Abstract

A load driving device (1) comprises: a driving control unit (3) which controls a switching circuit (2) that opens and closes a power supply path (L1); and a circuit protection mechanism (4) which protects the switching circuit (2) when a power supply anomaly occurs. The switching circuit (2) has a switching element (21), an input terminal unit (T1) into which a driving instruction signal (S1) is input, and an output terminal unit (T2) to which a load (L) is connected. The circuit protection mechanism (4) has a protection diode (D1) to the input terminal unit (T1)-side of which an anode terminal is connected and to the output terminal unit (T2)-side of which a cathode terminal is connected, a power supply anomaly detection unit (41) which detects an earth-fault anomaly on the basis of a voltage detection signal (S2) of a detection point (P1) between the input terminal unit (T1) and the protection diode (D1), and an earth-fault protection element (40) which is connected between the input terminal unit (T1) and the protection diode (D1) and which restricts the lower-limit level of the driving instruction signal (S1) when an earth-fault anomaly occurs.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Patent Application No. 2021-137349 filed on August 25, 2021, the contents of which are incorporated herein by reference. [Technical field]

[0002] The present disclosure relates to a load driver used for powering a load. [Background technology]

[0003] In a vehicle control system, it is mandatory to diagnose an abnormality in a path for supplying power to a sensor device related to exhaust gas treatment. In general, the power source and the sensor device are connected via a load drive device equipped with a switching circuit, and when an abnormality such as a short circuit or a break in the power supply path is detected, an abnormality detection signal is output from the load drive device to the outside. In addition, it is being considered to add a function to protect the internal circuit of the load drive device when an abnormality occurs.

[0004] For example, Patent Document 1 discloses a circuit configuration for detecting ground faults in a switching circuit for an in-vehicle device, in which a microcomputer interface circuit consisting of two resistors is connected in parallel with a load on the output side of a transistor, and a microcomputer is connected to this so that the output voltage of the transistor can be determined by the microcomputer. In this configuration, when the microcomputer detects a drop in output voltage due to a ground fault, it turns off the transistor, thereby preventing a large current from continuing to flow and protecting the transistor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-317545 Summary of the Invention

[0006] For example, an in-vehicle sensor device uses a load driver to control power supply to a heater section, which serves as a load. A switching circuit has a switching element that is turned on and off in response to a drive command from a control section, thereby opening and closing a power supply path to the heater section and maintaining the sensor device at a predetermined temperature. The control section can be configured to monitor, for example, the voltage or current of the power supply path, diagnose the presence or absence of a ground fault or the like, and stop the power supply operation when an abnormality is detected.

[0007] However, when a ground fault occurs, overheating due to overcurrent can easily cause problems such as damage to circuit elements or malfunction, so it is desirable to stop the power supply as quickly as possible. Furthermore, it has been found that in a load driving device that uses an on-board battery as a power source, if the wiring between the on-board battery and the device becomes long due to restrictions on placement within the vehicle, a high-frequency surge is more likely to occur in the event of a ground fault, which may lead to damage to the internal circuit. This is due to the inductance and capacitance components in the ground fault path, and it is believed that if the surge current that flows around from the ground side becomes large, it may exceed the set tolerance of the circuits for detecting ground faults and driving loads.

[0008] An object of the present disclosure is to provide a load driving device that can quickly stop power supply operation in the event of a ground fault and protect the circuit from a high-frequency surge that occurs in the event of a ground fault.

[0009] One aspect of the present disclosure is A load driving device including a switching circuit that opens and closes a power supply path from a power source to a load, a drive control unit that controls driving of the switching circuit, and a circuit protection mechanism that protects the switching circuit when a power supply abnormality occurs, The switching circuit is A voltage-driven switching element; an input terminal unit to which a drive instruction signal is input from the drive control unit; an output terminal portion to which the load is connected via a power supply line that serves as the power supply path; The circuit protection mechanism is as follows: a protection diode having an anode terminal connected to the input terminal section and a cathode terminal connected to the output terminal section; a power supply abnormality detection unit that detects a ground fault abnormality in the power supply path based on a voltage detection signal at a detection point provided between the input terminal unit and the protection diode; The load driving device has a ground fault protection element connected between the input terminal portion and the protection diode, and which limits the lower limit level of the drive instruction signal input to the switching circuit in the event of a ground fault abnormality. Another aspect of the present disclosure is A load driving device including a switching circuit that opens and closes a power supply path from a power source to a load, a drive control unit that controls driving of the switching circuit, and a circuit protection mechanism that protects the switching circuit when a power supply abnormality occurs, The switching circuit is A voltage-driven switching element; an input terminal unit to which a drive instruction signal is input from the drive control unit; an output terminal portion to which the load is connected via a power supply line that serves as the power supply path; The circuit protection mechanism is as follows: a protection diode having an anode terminal connected to the input terminal section and a cathode terminal connected to the output terminal section; a power supply abnormality detection unit that detects a ground fault abnormality in the power supply path based on a voltage detection signal at a detection point provided between the input terminal unit and the protection diode; In the event of a ground fault a ground fault protection element for limiting a lower limit level of the drive instruction signal input to the switching circuit, And, The earth fault protection element is a capacitor element having one terminal connected between the input terminal portion and the protection diode and the other terminal grounded. In the load driver.

[0010] In the load driving device having the above configuration, the switching circuit drives the switching element to open and close based on a drive instruction signal input from the input terminal section, and supplies power to the load via a power supply line connected to the output terminal section. When a ground fault occurs in the power supply path on the output side of the switching circuit, a current flows through a protection diode whose cathode terminal is connected to the output terminal section, and the voltage level of the drive instruction signal input to the input terminal section whose anode terminal is connected drops. This immediately turns off the switching element, making it possible to protect the switching element from overheating due to overcurrent. Moreover, by monitoring this drop in voltage level with a power supply abnormality detection section, it is possible to detect the occurrence of a ground fault. The protection diode protects the input terminal section so that the voltage on the power supply side is not applied during normal operation.

[0011] Furthermore, in the case of a high-frequency surge caused by a ground fault, the ground fault protection element connected between the input terminal unit and the protection diode operates to limit the lower limit level of the drive instruction signal, thereby protecting the switching circuit from surge currents that sneak in from the ground side. In this way, the circuit protection mechanism includes a protection diode, a power supply abnormality detection unit using the protection diode, and a ground fault protection element, so that the internal circuitry and switching elements of the switching circuit can be quickly protected while the occurrence of a ground fault can be reliably detected.

[0012] As described above, according to the above aspect, it is possible to provide a load driving device that can quickly stop the power supply operation in the event of a ground fault and protect the circuit from a high-frequency surge that occurs in the event of a ground fault. [Brief description of the drawings]

[0013] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: [Figure 1] FIG. 1 is a circuit diagram showing an overall configuration of a load driving device according to a first embodiment; [Diagram 2] FIG. 2 is a circuit diagram showing a current path in the load driving device in the first embodiment when a ground fault occurs; [Diagram 3] FIG. 3 is a time chart for explaining a ground fault detection operation by a circuit protection mechanism of a load driving device in accordance with the first embodiment; [Figure 4] FIG. 4 is a time chart for explaining a basic operation of a circuit protection mechanism of a load driving device in the first embodiment; [Diagram 5] FIG. 5 is a voltage waveform diagram at section A for explaining the effect of a circuit protection mechanism of the load driving device according to the first embodiment; [Figure 6] FIG. 6 is an overall configuration diagram and an equivalent circuit diagram of a load driving device according to the first embodiment; [Figure 7] FIG. 7 is a voltage waveform diagram of part A when a ground fault occurs in the load driving device according to the first embodiment; [Figure 8] FIG. 8 is a diagram showing a relationship between a power harness length and a peak voltage of a load driving device according to the first embodiment; [Figure 9] FIG. 9 is an equivalent circuit diagram of a load driver according to the first embodiment; [Figure 10] FIG. 10 is a voltage waveform diagram at section A for explaining the effect of a circuit protection mechanism of the load driving device according to the first embodiment; [Figure 11] FIG. 11 is a diagram showing a comparison of the relationship between the power harness length and the peak voltage depending on whether or not a resistive element is added to the load driving device in the first embodiment; [Figure 12] FIG. 12 is a diagram showing a relationship between an added resistance value to a load driving device and a voltage at part A in the first embodiment; [Figure 13] FIG. 13 is a circuit diagram showing an overall configuration of a load driving device according to a second embodiment; [Figure 14] FIG. 14 is an equivalent circuit diagram for explaining a configuration of a load driving device in a second embodiment; [Figure 15] FIG. 15 is a time chart showing the configuration of the load driving device according to the first and second embodiments and the first reference embodiment, and comparing the changes in the A section voltage and the B section voltage when a ground fault occurs; [Figure 16]FIG. 16 is a diagram showing a comparison of the relationship between the power harness length and the peak voltage depending on whether or not a capacitor element is added to a load driving device in the second embodiment; [Figure 17] FIG. 17 is a diagram showing the relationship between the capacitance value of a capacitor added to the load driving device and the peak voltage in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] (Embodiment 1) A first embodiment of a load driving device will be described with reference to FIGS. 1, the load driving device 1 of this embodiment includes a switching circuit 2 that opens and closes a power supply path L1 from a power source B to a load L, a drive control unit 3 that controls the driving of the switching circuit 2, and a circuit protection mechanism 4 that protects the switching circuit 2 in the event of a power supply abnormality. The power source B is, for example, an in-vehicle battery, and the load driving device 1 is used to supply battery power to various electrical devices such as a sensor S mounted on the vehicle. The load L is, for example, a heater unit built into the sensor S.

[0015] The switching circuit 2 has a voltage-driven switching element 21, an input terminal unit T1 to which a drive instruction signal S1 is input from the drive control unit 3, and an output terminal unit T2 to which a load L is connected via a power supply line L11 that serves as a power supply path L1. Preferably, the switching circuit 2 further includes a power supply terminal unit Tb and a gate driver unit (hereinafter, appropriately abbreviated to driver unit) 22. Here, "connection" means electrical connection, and the same applies hereinafter.

[0016] In the switching circuit 2, the power supply terminal unit Tb is connected to the power supply B via a power supply harness H which serves as a power supply path L1. The switching element 21 is connected in series between the power supply terminal unit Tb and the output terminal unit T2, and opens and closes the power supply path L1. The driver unit 22 is connected between the input terminal unit T1 and a gate terminal of the switching element 21, and can drive the switching element 21 based on a drive instruction signal S1.

[0017] The drive control unit 3 is connected to the input terminal unit T1 via a drive signal line L2, and can be configured to output a drive instruction signal S1, which is a binary voltage signal, to the switching circuit 2. The circuit protection mechanism 4 includes a protection diode D1, a power supply abnormality detection unit 41 using the protection diode D1, and a ground fault protection element 40.

[0018] The protection diode D1 has an anode terminal connected to the input terminal T1 side of the switching circuit 2, and a cathode terminal connected to the output terminal T2 side, and under normal conditions, protects the input terminal T1 from being applied with a voltage from the power supply side. In the event of a ground fault, a ground fault current path is formed that passes through the protection diode D1, and the signal level of the drive instruction signal S1 is reduced, thereby enabling the switching element 21 to be immediately turned off.

[0019] The power supply abnormality detection unit 41 provides a detection point P1 between the input terminal unit T1 and the protection diode D1, and detects a ground fault abnormality in the power supply path L1 based on a voltage detection signal S2 at the detection point P1. Preferably, the power supply abnormality detection unit 41 is connected to the detection point P1 via a detection signal line L3, and periodically monitors the potential of the detection point P1, which is input as the voltage detection signal S2, thereby making it possible to detect a ground fault abnormality by utilizing a voltage drop in the ground fault current path caused by the protection diode D1.

[0020] The circuit protection mechanism 4 further includes a ground fault protection element 40 to protect the circuit from a high-frequency surge caused by a ground fault. The ground fault protection element 40 is connected between the input terminal T1 and the protection diode D1, and limits the lower limit level of the drive instruction signal S1 input to the switching circuit 2 in the event of a ground fault. Specifically, the ground fault protection element 40 operates so that the minimum value of the voltage signal input to the input terminal T1 in the event of a ground fault, i.e., the lower limit signal level of the drive instruction signal S1, does not fall below the set withstand voltage of the switching circuit 2.

[0021] A resistor element R1 connected in series between the input terminal T1 and the protection diode D1 can be preferably used as the ground fault protection element 40. The resistor element R1 is disposed in a current path in the event of a ground fault and consumes the ground fault surge current that occurs, thereby suppressing the negative fluctuation of the drive instruction signal S1 and quickly protecting the switching circuit 2.

[0022] In the present embodiment, the following description will be given as an example in which a resistor element R1 for earth fault protection is used in the circuit protection mechanism 4. The resistor element R1 is preferably configured as, for example, a chip resistor, and is disposed in the current path in the event of an earth fault closer to the input terminal T1. It is preferably disposed closer to the input terminal T1 than the detection point P1, and can be inserted in series, for example, between the connection point P2 between the protection diode D1 and the drive signal line L2, and the input terminal T1.

[0023] The drive control unit 3 and the power supply abnormality detection unit 41 can be configured as a part of a control device 5 that controls the overall operation of the sensor S, including the driving of the heater unit by the load drive device 1. The control device 5 is configured by a microcomputer (hereinafter, appropriately referred to as a microcomputer) that has a memory for storing programs and the like and a CPU and executes arithmetic processing and the like based on the programs.

[0024] Here, as shown by the dashed arrow in Fig. 2, if a ground fault occurs in the power supply line L11 to the load L, there is a risk that a current due to a high-frequency surge will flow to the ground side without passing through the load L and will sneak into the input side of the switching circuit 2 from the ground terminal Tg. In this case, as shown by the solid arrow in Fig. 2, a current path is formed that connects the input side and output side of the switching circuit 2 via the protection diode D1, causing a drop in the voltage signal level input to the input terminal T1.

[0025] That is, as shown in FIG. 3, in the event of a ground fault, the voltage detection signal S2 at the detection point P1 is equal to the forward voltage V f1 Therefore, this voltage V f1However, if this is set so that it corresponds to a low-level signal of the drive instruction signal S1 and is recognized in the driver section 22 as a signal level that turns off the switching element 21, the switching element 21 can be immediately turned off due to the drop in the voltage signal level.

[0026] Moreover, a ground fault can be detected by monitoring this drop in the voltage signal level with the power supply abnormality detection unit 41. Specifically, the occurrence of a ground fault can be detected by periodically capturing the potential of the detection point P1 and comparing it with a preset ground fault detection threshold value TH.

[0027] 4 shows the relationship between the ground fault detection operation in the power supply abnormality detection unit 41 and the operation of each unit, with the voltage at the input terminal T1 of the switching circuit 2 being the A section voltage and the voltage at the output terminal T2 being the B section voltage. When a ground fault occurs in a state where the load driving device 1 is operating normally, the A section voltage (i.e., the signal level of the drive instruction signal S1) drops from high level as the B section voltage drops, and when the A section voltage falls below the ground fault detection threshold TH, a ground fault is detected. That is, at the timing when the voltage detection signal S2 is taken into the power supply abnormality detection unit 41, the recognized voltage in the control device 5 (i.e., the microcomputer recognized voltage in FIG. 4) switches from high level to low level.

[0028] As a result, when the drive control unit 3 stops the operation of outputting the drive instruction signal S1, the input of the drive instruction signal S1 to the driver unit 22 of the switching circuit 2 is stopped. However, a delay may occur before the drive instruction operation by the drive control unit 3 is stopped, depending on the timing of the ground fault detection and the arithmetic processing in the control device 5. Even in such a case, since the switching element 21 can be turned off at the point in time when the section A voltage drops to a low level regardless of the drive instruction operation, the switching operation can be stopped more quickly.

[0029] Furthermore, as shown in Fig. 5, for high-frequency surges that occur when a ground fault occurs, the fluctuation of the voltage signal level can be suppressed by inserting a resistive element R1 into the current path when a ground fault occurs (for example, as shown by the solid line in Fig. 5). This significantly reduces the negative surge (hereinafter, appropriately referred to as a negative surge) compared to when the resistive element R1 is not provided (for example, as shown by the dotted line in Fig. 5), and prevents problems caused by the negative surge leaking into the input side of the switching circuit 2. In addition, the signal level input to the switching circuit 2 is stabilized, enabling quick detection of a ground fault.

[0030] In this way, the load driving device 1 of this embodiment is equipped with a circuit protection mechanism 4, and is able to detect a ground fault anomaly in the power supply path L1 to which the load L is connected, and quickly stop driving the switching circuit 2, thereby protecting the circuit from overcurrent and high-frequency surges caused by ground faults.

[0031] The load driving device 1 of this embodiment will be described in detail below. In FIG. 1, a sensor S for mounting on a vehicle to which the load driving device 1 is applied is, for example, a gas sensor such as a NOx sensor constituting an exhaust gas treatment device, and a heater portion (for example, a resistor R H A sensor element incorporating a NOx detector 11 is installed in an exhaust gas passage of a vehicle. The load driver 1 supplies power via a power supply path L1 to cause the heater section to generate heat, thereby heating the sensor element to a temperature suitable for detecting NOx.

[0032] The power supply path L1 is a path for supplying a DC power supply voltage VD from a power source B to a load L, and the load driving device 1 includes a control device 5 having a switching circuit 2 for opening and closing the power supply path L1 and a drive control unit 3 for controlling the switching circuit 2. The control device 5 controls the power supply to the load L using the drive control unit 3, and also controls the overall operation of the sensor S including a NOx detection unit (not shown) that is built into the sensor element together with a heater unit.

[0033] The switching circuit 2 is configured as a high-side switch IC, and includes a switching element 21, a driver unit 22, and various terminal units. A power source B is connected to a power source terminal unit Tb of the switching circuit 2 via a power source harness H (e.g., inductance Lv, resistance Rv), and a load L is connected to an output terminal unit T2 of the switching circuit 2 via a power supply line L11. At this time, a path extending from the power source harness H continuing to the power source B through the inside of the switching circuit 2 and the power supply line L11 to the load L is the power supply path L1.

[0034] The switching element 21 is connected in series to the power supply path L1 between the power supply terminal section Tb and the output terminal section T2, and is turned on and off by a driver section 22 connected to the input terminal section T1 to make or break the power supply path L1. For example, a gate voltage-driven MOSFET (i.e., a field effect transistor) is used as the switching element 21, and the drain terminal of the MOSFET is connected to the power supply terminal section Tb, and the source terminal of the MOSFET is connected to the output terminal section T2. ​​The driver section 22 is connected to the gate terminal of the MOSFET.

[0035] A drive instruction signal S1 is input to the driver unit 22 via a drive signal line L2 connected to an input terminal unit T1 of the switching circuit 2. The drive instruction signal S1 is a binary voltage signal of high level (H) or low level (L) generated in a drive control unit 3 of the control device 5 (see, for example, FIG. 3), and the driver unit 22 outputs a gate signal for turning on and off the switching element 21 based on the signal level of the input drive instruction signal S1. The drive control unit 3 generates the drive instruction signal S1 based on, for example, a temperature detection result of the load L, and controls the on / off operation of the switching element 21 so that the sensor S is maintained at a predetermined temperature.

[0036] In the switching circuit 2, the driver unit 22 and the protection diode D2 are connected in parallel between the input terminal unit T1 and the ground terminal Tg, and the reverse connection protection resistor R2 is connected in series between the driver unit 22 and the ground terminal Tg. The protection diode D2 has a cathode terminal connected to a signal line L21 connecting the input terminal unit T1 and the driver unit 22, and an anode terminal connected to a ground line L4 between the driver unit 22 and the reverse connection protection resistor R2. The protection diode D2 is set, for example, so as to ensure a predetermined surge resistance against electrostatic surges input from the input terminal unit T1. The reverse connection protection resistor R2 is set, for example, so as to protect the circuit by reducing the voltage when the power source B is connected in the reverse direction.

[0037] In this way, the high-side switch IC that constitutes the switching circuit 2 is usually configured to have a protective diode D2 and a reverse connection protection resistor R2 built in to protect the internal circuitry. However, the settings of a typical high-side switch IC are not necessarily sufficient to protect the switching circuit 2 when a ground fault occurs in the power supply path L1 that connects the heater part of the sensor S to the load L.

[0038] Therefore, in this embodiment, a circuit protection mechanism 4 is provided outside the switching circuit 2 to reliably protect the switching circuit 2 from a ground fault. The circuit protection mechanism 4 includes a protection diode D1 and a power supply abnormality detection unit 41 using the protection diode D1, and detects a ground fault in the power supply path L1 and quickly stops the switching element 21. The circuit protection mechanism 4 further includes a resistance element R1 as a ground fault protection element 40, and reliably protects the switching circuit 2 from a surge current that occurs in the event of a ground fault.

[0039] The protection diode D1 has an anode terminal connected to the drive signal line L2 leading to the input terminal section T1 of the switching circuit 2, and a cathode terminal connected to the power supply line L11 leading to the output terminal section T2 of the switching circuit 2. At this time, the protection diode D1 is connected between the input terminal section T1 and the output terminal section T2 of the switching circuit 2, with the direction from the drive signal line L2 to the power supply line L11 being the forward direction. This prevents the voltage of the power supply line L11 (i.e., ≈ power supply voltage VD) from being applied to the input terminal section T1 under normal conditions, making it possible to prevent damage to the internal circuitry due to overvoltage.

[0040] In addition, when a high-frequency surge occurs due to a ground fault, as shown by the dotted line in Figure 2, the load L (i.e., resistance R H ), a current path is formed that passes through a ground-fault location with lower resistance (i.e., resistor Rs) and returns from the ground terminal Tg to the input terminal T1 side of the switching circuit 2. This current path forms a closed circuit that runs from the drive signal line L2, via the protective diode D1, to the power supply line L11 on the output terminal T2 side of the switching circuit 2.

[0041] At this time, the power supply abnormality detection unit 41 detects the ground fault abnormality based on the potential of a detection point P1 provided on the anode terminal side of the protection diode D1 in the ground fault current path. The detection point P1 is provided between the protection diode D1 and the drive signal line L2, and is connected to the power supply abnormality detection unit 41 via the detection signal line L3. The power supply abnormality detection unit 41 is provided with a ground fault detection circuit 42 that determines the presence or absence of a ground fault abnormality, and a drive prohibition unit 43 that prohibits the output of the drive instruction signal S1 when a ground fault abnormality occurs.

[0042] 3, in response to a drive instruction signal S1 output from the drive control unit 3 to the drive signal line L2, a voltage detection signal S2 at a detection point P is input from the detection signal line L3 to the ground fault detection circuit 42 at a predetermined timing. Here, at time T0 in FIG. 3, when the drive instruction signal S1 is at a high level and a ground fault abnormality occurs in the power supply path L1, the voltage level of the voltage detection signal S2 input to the ground fault detection circuit 42 becomes equal to or lower than the forward voltage V of the protection diode D1.f1 It drops to.

[0043] Therefore, the ground fault detection circuit 42 can be configured to set a detection threshold value TH for detecting a ground fault in advance, and to determine that a ground fault has occurred when the voltage detection signal S2 has a voltage level lower than the detection threshold value TH using a comparison circuit or the like. The detection threshold value TH in the ground fault detection circuit 42 is a sum of the high level voltage (for example, about 5 V) of the drive instruction signal S1 and the forward voltage V of the protection diode D1. f1 It is set to be between

[0044] When it is determined that a ground fault has occurred, the ground fault detection circuit 42 can output a ground fault signal S0 to an external vehicle control device (not shown), for example, to warn of the abnormality in the sensor S. In addition, the drive inhibition unit 43 can be operated to output a drive inhibition signal S3 to the drive control unit 3. The drive control unit 3 is configured so that when the drive inhibition signal S3 is input while the drive instruction signal S1 is being output (i.e., high level), the output of the drive instruction signal S1 is stopped (i.e., low level), or the drive instruction signal S1 is output only when the drive inhibition signal S3 is not input.

[0045] However, as described above, if a delay occurs in the detection operation by the ground fault detection circuit 42 and the stop of the drive instruction signal S1 is delayed, there is a risk of a malfunction such as overheating of the switching element 21. Furthermore, if a high-frequency surge generated with the occurrence of a ground fault becomes large at time T0 in FIG. 3, this may lead to damage to the internal circuit of the switching circuit 2. For this reason, a protection diode D1 and a resistance element R1 are arranged in the current path in the event of a ground fault, and as shown in FIGS. 4 and 5, the drive of the switching element 21 is promptly stopped and the input of a high-frequency surge generated in the event of a ground fault is limited. Thereafter, the operation of the switching circuit 2 can be reliably stopped by the output of the drive inhibition signal S3 from the drive inhibition unit 43.

[0046] Next, the mechanism by which earth fault detection and a ground fault leads to circuit destruction will be described with reference to reference embodiment 1 shown in Figures 6 to 8. As shown in the left diagram of Figure 6, reference embodiment 1 shows the basic circuit configuration of this embodiment, and is the same as the load driving device 1 of Figure 1 above, except that the circuit protection mechanism 4 does not include a resistive element R1, and includes a power supply abnormality detection unit 41 using a protective diode D1. The right diagram of Figure 6 shows a simplified circuit excluding the switching circuit 2 and the control device 5, and in the event of an earth fault, an earth fault current I that flows through a resistor Rs at the earth fault location flows inversely to a current Iv that flows from the power harness H to the load L when a power supply voltage VD is applied. short flows from the ground terminal Tg side to the forward direction of the protection diode D1. f2 is the forward voltage of the protective diode D2, and R GRD indicates the resistance value of the reverse connection protection resistor R2.

[0047] Here, when paying attention to the input side of the switching circuit 2, the voltage (i.e., the voltage V A ) is the voltage on the output side (i.e., the voltage at part B, V B ) and the forward voltage V of the protection diode D1 f1 Using this, it is expressed by the following equation (1). V A =V B +V f1 ...Equation (1) During a ground fault, V B ≒0V, so the voltage at part A during a ground fault is V A is expressed by the following formula (2), and V f1 is almost equivalent. V A ≒V f1 ...Equation (2)

[0048] As shown in Figure 7, the voltage V A is normally at the same signal level as the drive instruction signal S1, and when a ground fault occurs, V f1 In other words, this voltage drop can be detected as a ground fault by the power supply abnormality detection unit 41. Ais taken in as a voltage detection signal S2 at the detection point P1 and compared with a ground fault detection threshold TH (see FIG. 3, for example). The ground fault detection threshold TH is lower than the signal level recognized as a high level, and V f1 (i.e., H level>TH>V f1 >0).

[0049] However, if a high-frequency surge generated during a ground fault exceeds the range of the circuit withstand voltage indicated by the dashed line in Fig. 7, the circuit may be destroyed. The upper or lower limit of the withstand voltage of the switching circuit 2 (i.e., the destruction limit) is generally set based on the high or low level signal of the drive instruction signal S1, and the withstand voltage setting for a negative side surge is lower than that for the positive side. For this reason, if the negative surge becomes large due to the influence of the wiring length of the power supply path L1, the lower limit of the circuit withstand voltage may be exceeded, causing damage to the circuit components.

[0050] On the other hand, when a ground fault occurs, the voltage V A The minimum value of V, i.e., the negative peak value V due to the high frequency surge A-peak is expressed by the following formula (3) using the wiring length X of the power harness H (hereinafter, appropriately referred to as the power harness length). V A-peak ={a / (bX+c)}+d×eX...Equation (3) In equation (3), a, b, c, d, and e are constants that are determined by the circuit configuration. Equation (3) is expressed as follows: The power harness length X is proportional to the resistance Rv and inductance Lv of the power harness H (i.e., X∝Rv∝Lv), and the voltage V at part B is calculated as B It is calculated based on the formula (31). V B =V B-DC +V B-AC ...Equation (31) In formula (31), V B-DC V B is the DC component of V B-AC V B is the AC component of Details of this will be provided later.

[0051] Figure 8 shows the relationship between the power harness length X (unit: mm) and the peak value V A-peak (unit: V) relationship. As the power harness length X increases from 0 mm, the peak value V A-peak The voltage drops, and the risk of reaching the voltage breakdown region increases. This trend continues until the power harness length X exceeds 10,000 mm (i.e., region X1), and then converges to a substantially constant range (i.e., region X2). Therefore, measures are needed to reliably prevent circuit breakdown due to ground faults in large vehicles and commercial vehicles in which the power harness length X is relatively long.

[0052] Therefore, in this embodiment, in addition to the power supply abnormality detection unit 41 of the circuit protection mechanism 4, a resistance element R1 is arranged in the current path at the time of a ground fault, so that the high frequency surge is A FIG. 9 is an equivalent circuit diagram showing the configuration of this embodiment in which a resistive element R1 (for example, resistance value R) is added, and the A part voltage V' A is expressed by the following equation (41). V' A =V B +V f1 +R×I short ...Equation (41) Here, from the above formula (1), V A =V B +V f1 Therefore, the above equation (41) can be expressed as the following equation (42). V' A =V A +R×I short ...Formula (42) Therefore, the voltage at part A, V' A Peak value V' A-peak When taking into account the above equation (3), it is expressed by the following equation (4). V' A-peak =V A-peak +R×I short ={a / (bX+c)}+d×eX+R×I short ...Equation (4)

[0053] As a result, the peak value V'A-peak Voltage V' at part A including A The whole of R×I short By adding the resistor element R1, it is possible to raise the voltage V' at part A to within the range of the circuit withstand voltage. A The voltage of part A before the addition, V A This creates an offset in the positive direction for the peak value V' A-peak Therefore, it is possible to set the value so that it does not fall below the lower limit of the circuit withstand voltage.

[0054] Figure 11 shows the relationship between the power harness length X (unit: mm) and the peak value V A-peak 11 shows the relationship between the power harness length X and the peak value V A-peak The relationship between the peak value V and the peak value V shows the same tendency as in Fig. 8, but is largely offset in the positive direction overall. A-peak The size of the power harness H is significantly reduced overall, and it is possible to prevent the power harness H from reaching the destruction limit region regardless of its length.

[0055] 12 shows an example of a simulation result in which a resistive element R1 is placed on the input side of the switching circuit 2 and its resistance value R (unit: kΩ) is changed. For a breakdown voltage (e.g., lower limit: −0.3 V) set in the driver unit 22 of the switching circuit 2, the resistance value R can be determined by solving the following equation (5). V' A-peak ≧V break ...Equation (5) In formula (4), V break is the driver breakdown voltage, and V' A-peak is a function of the power harness length X and resistance value R expressed by the above equation (4).

[0056] From the results of FIG. 8 described above, in a circuit configuration without the resistive element R1, when the power harness length X is 30,000 mm, the voltage V A Peak value of V A-peakTherefore, in Fig. 12, the voltage V at part A is plotted against the power harness length X in the above formula (4) as 30,000 mm, and the resistance R is changed. A As shown in the figure, the larger the resistance R, the lower the voltage V A is increasing, and if the resistance value R is set to 30 kΩ or more, it can be seen that the above formula (5) is established.

[0057] The above formula (3) is calculated as follows. In the equivalent circuit of FIG. 9, as shown in the above formula (31), the voltage V at part B is B is the DC component (V B-DC ) and AC component (V B-AC Of these, the DC component (V B-DC ) is the resistance Rv of the power harness H and the resistance R of the load L connected in parallel H and the resistance of the earth fault point Rs (i.e., R H / / R S ) and the voltage is divided by this and expressed by the following equation (32). V B-DC =V D ×{R H ·R S / (R H ·R S +R V ·R S +R V ·R H )}...Equation (32) When this equation (32) is transformed using constants A, B, and C, it can be expressed as the following equation (33). V B-DC =A / (BR V +C)...Formula (33) A:V D ·R H ·R S B:R H +R S C:R H ·R S

[0058] On the other hand, AC component (V B-AC) is proportional to the electromotive force due to the inductance Lv of the power harness H, and is expressed by the following equation (34). V B-AC ∝Lv×(dIv / dt)...Equation (34) Here, the current Iv is expressed by the following equation (35), and therefore can be substituted into the above equation (34) to transform it into the following equation (36). Iv=V D ×{(R H +R S ) / (R V ·R H +R V ·R S +R H ·R S )}...Equation (35) V B-AC ∝Lv / R V =D×(Lv / R V )...Equation (36) D: Constant of proportionality

[0059] A section voltage V A The above formula (1) expresses the voltage V at part B. B The above equations (31), (33), and (36) representing the above are summarized as shown in the following equation (37). V A ={A / (BR V +C)}+V f1 +D×(Lv / R V )...Equation (37) Of these, the first term on the right side is a DC fluctuation term, the second term is a constant term, and the third term is an AC fluctuation term. As mentioned above, the power harness length X and resistance R V and inductance L V Since these are proportional, this equation (37) can be transformed using X. That is, X ∝ R V ∝L V Then, the following is obtained, which can be expressed as the above-mentioned equation (3). V A-peak ={a / (bX+c)}+d×eX...Equation (3)

[0060] Thus, according to the configuration of this embodiment, since the circuit protection mechanism 4 includes the resistive element R1, the signal level input to the switching circuit 2 during a ground fault can be maintained within the set voltage resistance range of the circuit. This makes it possible to quickly reduce the signal level input to the driver unit 22 and turn off the switching element 21 while preventing circuit destruction due to a high-frequency surge. Therefore, by combining ground fault detection by the power supply abnormality detection unit 41 using the protective diode D1 and ground fault protection by the resistive element R1, it is possible to reliably protect the switching circuit 2.

[0061] (Embodiment 2) A second embodiment of the load driving device will be described with reference to FIGS. 13, the load driving device 1 of this embodiment uses a capacitor element C1 instead of the resistor element R1 in the first embodiment as a ground fault protection element 40 connected between the input terminal T1 and a protection diode D1 in the circuit protection mechanism 4. The basic configuration of the load driving device 1 is the same as that of the first embodiment, and the following description will focus on the differences. In addition, among the symbols used in the second and subsequent embodiments, the same symbols as those used in the previous embodiments represent the same components, etc. as those in the previous embodiments, unless otherwise specified.

[0062] In this embodiment as well, the load driving device 1 includes a circuit protection mechanism 4 that protects the switching circuit 2, which opens and closes the power supply path L1, when the switching circuit 2 is driven in response to a drive command from a drive control unit 3 of a control device 5. The circuit protection mechanism 4 detects a ground fault by a protection diode D1 that forms a current path in the event of a ground fault, and a power supply abnormality detection unit 41 that uses the protection diode D1, and protects the switching circuit 2 in the event of a ground fault abnormality by using a capacitor element C1 as a ground fault protection element 40. The capacitor element C1 can be configured as a chip capacitor integrated to have a predetermined capacitance value C, for example.

[0063] One of the terminals of the capacitor element C1 is connected to the drive signal line L2 between the input terminal T1 and the drive control unit 3, and the other terminal is connected to the ground line L4 between the reverse connection protection resistor R2 and the ground terminal Tg. A protection diode D1 is connected to a connection point P2 between the capacitor element C1 and the drive signal line L2 via a detection point P1. That is, the capacitor element C1, which is the ground fault protection element 40, is connected in parallel to the ground fault current path from the ground terminal Tg through the input terminal T1 to the protection diode D1, and it becomes possible to absorb a surge current generated in the event of a ground fault. With this configuration, it is possible to suppress the fluctuation of the drive instruction signal S1, limit the decrease in the signal level, and quickly protect the switching circuit 2 in the event of a ground fault abnormality.

[0064] In this way, the ground fault protection element 40 may be any element that is connected between the input terminal T1 and the protection diode D1 and operates so that the lower limit level of the drive instruction signal S1 input to the input terminal T1 does not fall below the allowable limit of the switching circuit 2. By using the capacitor element C1, the signal level of the drive instruction signal S1 is prevented from changing significantly to the negative side, and the signal level can be gradually decreased toward the minimum value.

[0065] The equivalent circuit diagram shown in FIG. 14 is a configuration in which a capacitor element C1 (for example, a capacitor with a capacitance value of C) is added to the basic circuit of this embodiment shown in FIG. 6. A Voltage V” at part A A is expressed by the following equation (6). V” A =V A ×E×(1-exp(-F / C))+H...Equation (6) In equation (6), E, ​​F, and H are constants that are determined depending on the circuit configuration. Therefore, the voltage at part A, V A The minimum peak value V A-peak Taking into account the above equation (3), it is expressed by the following equation (7). V” A-peak =V A-peak ×E×(1-exp(-F / C))+H...Equation (7) =[{a / (bX+c)}+d×eX]×E×(1-exp(-F / C))+H...Equation (7) The above formula (6) will be described in detail later.

[0066] FIG. 15 shows the voltage V″ at part A in this embodiment. A 15 shows a waveform at the time of occurrence of a ground fault, in comparison with the waveforms in the above-mentioned embodiment 1 and reference embodiment 1. The top row of FIG. 15 shows a comparative embodiment without the protection diode D1 and the ground fault protection element 40 (i.e., the resistor element R1 or the capacitor element C1). In that case, the A part voltage has a waveform equivalent to the B part voltage, and the B part voltage is applied to the switching circuit 2, which may exceed the upper breakdown limit. Also, the lower breakdown limit may be exceeded due to a high-frequency surge at the time of a ground fault. In contrast, in reference embodiment 1 in which the protection diode D1 is added, the voltage applied to A part is limited, and in embodiment 1, the resistor element R1 is further added to consume the high-frequency surge, and the A part voltage is maintained within a range that does not exceed the breakdown limit.

[0067] 15, in this embodiment, the A part voltage is absorbed by the parallel connection of the capacitor element C in such a way that the surge flowing through the ground-fault current path is absorbed, and the voltage fluctuation on the input side of the switching circuit 2 is suppressed. As a result, the A part voltage gradually drops from the signal level (high-level voltage) at which the switching element 21 is turned on to the signal level (low-level voltage) at which the switching element 21 is turned off. As a result, the A part voltage is maintained within a range that does not exceed the breakdown limit.

[0068] Figure 16 shows the relationship between the power harness length X (unit: mm) and the peak value V A-peak The relationship between the capacitance and the capacitance of the capacitor C1 and the peak value V A-peak is largely offset in the positive direction overall. Therefore, the peak value V A-peak This suppresses the decrease in the power supply voltage, and makes it possible to prevent the power supply harness H from reaching the breakdown limit region regardless of its length.

[0069] 17 shows an example of a simulation result in which a capacitor element C1 is connected in parallel between the input side of the switching circuit 2 and the ground terminal Tg, and the capacitor capacitance value C (unit: μF) is changed. For a breakdown voltage (e.g., lower limit: −0.3 V) of the driver unit 22 of the switching circuit 2, the capacitor capacitance value C can be determined by solving the following equation (5), as in the first embodiment. V' A-peak ≧V break ...Equation (5)

[0070] As in the first embodiment, FIG. 17 shows the relationship between the A section voltage V and the capacitance C of the capacitor when the power harness length X is set to 30,000 mm. A As shown in the figure, the larger the capacitance value C of the capacitor, the lower the voltage V A is increasing, and it can be seen that if the capacitance value C of the capacitor is set to 13 μF or more, the above formula (5) is established.

[0071] The above formula (6) is calculated as follows. The voltage V" at part A when the capacitor element C1 is added A are expressed by the following equations (61) and (62). V” A =-R GRD ×Ig-V f2 ...Formula (61) V” A =-(1 / C)∫(Icdt)...Equation (62) In addition, the earth fault current I short is expressed by the following equation (63). I short =I G +I C =V B / Rs...Formula (63) In formulas (61) to (63), I G is the current flowing through the reverse polarity protection resistor R2, I C is the current flowing through the capacitor element C1.

[0072] From the above equations (61) to (63), the earth fault current I shortV f2 If we ignore this, it is expressed by the following equation (64). I short =-{(V” A +V f2 ) / R GRD}-C(dV” A / dt) =-(V” A / R GRD )-C(dV” A / dt)...Formula (64) The above equation (64) is a first-order differential equation, so when it is solved, it gives the following equation (65). V” A =R GRD ×Ishort×[1-exp{-t / (R GRD ·C)}]...Formula (65) When this equation (65) is transformed using the above equation (63), it becomes the following equation (66). V” A =(R GRD / Rs) × V B ×[1-exp{-t / (R GRD ·C)}]...Formula (66)

[0073] Furthermore, the following equation (67) is derived from the above equation (66) and the above equation (1). V” A =(R GRD / Rs)×(V A +V f1 )×[1-exp{-t / (R GRD C)}] =V A ×(R GRD / Rs)+[1-exp{-t / (R GRD ·C)}]-V f1 ×(R GRD / Rs)×[1-exp{-t / (R GRD ·C)}]...Formula (67) In this equation (67), E=(R GRD / Rs) F = {-t / (R GRD C)}] H=V f1 ×(R GRD / Rs)×[1-exp{-t / (R GRD C)}] Then, the following is obtained, which can be expressed as the above-mentioned equation (6). V” A =V A ×E×(1-exp(-F / C))+H...Equation (6)

[0074] With the configuration of this embodiment, since the circuit protection mechanism 4 includes the capacitor element C1, the same effect as in the above-described embodiment 1 can be obtained. That is, the signal level input to the switching circuit 2 in the event of a ground fault can be quickly reduced to turn off the switching element 21 while preventing circuit destruction due to a high-frequency surge, and the switching circuit 2 can be reliably protected.

[0075] The present disclosure is not limited to the above-mentioned embodiments, and can be applied to various embodiments without departing from the gist of the present disclosure. For example, the on-vehicle sensor S to which the load driving device 1 is applied may be mounted in an exhaust gas treatment device for a vehicle and detect various components contained in exhaust gas, and may be a gas sensor such as a NOx sensor, or a PM sensor for detecting particulate matter. The present disclosure can also be applied to a load device other than a heater portion provided in a sensor for a vehicle. In addition, although a MOSFET is exemplified as a voltage-driven switching element, a semiconductor power element other than a MOSFET, for example, an IGBT (insulated gate bipolar transistor), can also be used.

[0076] Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also encompasses various modifications and modifications within the equivalent range. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure.

Claims

1. A load driving device (1) including a switching circuit (2) that opens and closes a power supply path (L1) from a power source (B) to a load (L), a drive control unit (3) that controls the driving of the switching circuit, and a circuit protection mechanism (4) that protects the switching circuit in the event of a power supply abnormality, The switching circuit is A voltage-driven switching element (21); an input terminal unit (T1) to which a drive instruction signal (S1) from the drive control unit is input; an output terminal unit (T2) to which the load is connected via a power supply line (L11) that serves as the power supply path; The circuit protection mechanism is as follows: a protection diode (D1) having an anode terminal connected to the input terminal section and a cathode terminal connected to the output terminal section; a power supply abnormality detection unit (41) for detecting a ground fault abnormality in the power supply path based on a voltage detection signal (S2) at a detection point (P1) provided between the input terminal unit and the protection diode; a ground fault protection element (40) connected between the input terminal portion and the protection diode, for limiting a lower limit level of the drive instruction signal input to the switching circuit in the event of a ground fault abnormality.

2. 2. The load driving device according to claim 1, wherein the switching circuit has the switching element connected in series between a power supply terminal section (TB) connected to the power supply via a power supply harness (H) serving as the power supply path and the output terminal section, and a gate driver section (22) for driving the switching element is connected between the input terminal section and a gate terminal of the switching element.

3. 3. The load driving device according to claim 1, wherein the drive control section is connected to the input terminal section via a drive signal line (L2) and outputs the drive instruction signal, which is a binary voltage signal, to the switching circuit.

4. 4. The load driving device according to claim 3, wherein the ground fault protection element operates so that a minimum value of a voltage signal input to the input terminal portion in the event of a ground fault abnormality does not fall below a set withstand voltage of the switching circuit.

5. 4. The load driving device according to claim 1, wherein the ground fault protection element is a resistive element (R1) connected in series between the input terminal portion and the protection diode.

6. 6. The load driving device according to claim 5, wherein the resistance value of the resistive element is set to 30 k[Omega] or more.

7. A load driving device (1) comprising: a switching circuit (2) that opens and closes a power supply path (L1) from a power source (B) to a load (L); a drive control unit (3) that controls the driving of the switching circuit; and a circuit protection mechanism (4) that protects the switching circuit in the event of a power supply abnormality, The switching circuit is A voltage-driven switching element (21); an input terminal unit (T1) to which a drive instruction signal (S1) from the drive control unit is input; an output terminal unit (T2) to which the load is connected via a power supply line (L11) that serves as the power supply path; The circuit protection mechanism is as follows: a protection diode (D1) having an anode terminal connected to the input terminal section and a cathode terminal connected to the output terminal section; a power supply abnormality detection unit (41) for detecting a ground fault abnormality in the power supply path based on a voltage detection signal (S2) at a detection point (P1) provided between the input terminal unit and the protection diode; a ground fault protection element (40) that limits a lower limit level of the drive instruction signal input to the switching circuit when a ground fault occurs; The load driving device, wherein the earth fault protection element is a capacitor element (C1) having one terminal connected between the input terminal portion and the protection diode and the other terminal grounded.

8. 8. The load driving device according to claim 7, wherein the capacitance value of the capacitor element is set to 13 μF or more.

9. The power supply abnormality detection unit has a ground fault detection circuit (42) that compares the voltage detection signal with a ground fault detection threshold (TH) to determine the presence or absence of a ground fault abnormality, and a drive prohibition unit (43) that outputs a drive prohibition signal (S3) that prohibits the output of the drive instruction signal to the drive control unit when a ground fault abnormality occurs. The load driving device according to any one of claims 1 to 8.

10. 10. The load driving device according to claim 1, wherein the load is a heater section provided in an on-vehicle sensor (S).

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