JP2012194056A - Disconnection detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable detection of the disconnection of an energization circuit in the state where the energization circuit energizes an energization object.SOLUTION: An energization circuit is provided with a disconnection detecting coil 5 independent of a solenoid 1 being an energization object for detecting a potential at a portion between the coil 5 of the energization circuit and the solenoid 1 being the energization object as an energization object-side potential. Then, if the energization object-side potential becomes or exceeds an energization object-side threshold potential, a disconnection of the solenoid 1 and various disconnections of a part lower than the coil 5 are detected. Such detection of disconnection enables disconnection detection of the energization circuit in a state where a second transistor 4 for energizing the solenoid is turned on. Thus enabling the detection of disconnection in the aforementioned state prevents an influence on driving of an increase-pressure control valve as in the case of disconnection detection requiring the second transistor 4 to be turned off.

Description

  The present invention relates to a disconnection detection circuit that is applied to an energization circuit that supplies current to an energization target and detects disconnection of the energization circuit.

  Conventionally, in Patent Document 1, a solenoid disconnection diagnosis device that constitutes a disconnection detection circuit has been proposed. In this solenoid disconnection diagnostic device, a transistor is connected in series to the solenoid, a Zener diode is connected between the solenoid and the transistor, and the potential between the solenoid and the transistor is connected to the microcomputer and the gate of the transistor via the Zener diode. A corresponding potential is input.

  In such a configuration, if the solenoid is not disconnected, the flyback voltage generated by the solenoid that is the L load when the transistor is switched from ON to OFF exceeds the Zener breakdown voltage of the Zener diode. For this reason, when the transistor is switched from on to off, if the flyback voltage exceeds the Zener breakdown voltage of the Zener diode and the gate voltage is applied to the transistor, the solenoid is not disconnected and the gate voltage is applied. If it remains at 0V, it can be detected that the solenoid is disconnected.

Japanese Utility Model Publication No. 3-128868

  However, since the potential between the solenoid and the transistor is low level regardless of whether the solenoid is disconnected or not when the transistor is on, the solenoid is disconnected even if the solenoid is disconnected while the transistor is on. The disconnection cannot be detected. For this reason, in order to detect disconnection of the solenoid, the transistor must be switched from on to off.

  For example, the technique of Patent Document 1 is applied to a pressure increase control valve used for brake control, that is, detection of disconnection of a solenoid provided in a normally open valve that controls pressure increase of each wheel cylinder between a master cylinder and each wheel cylinder. can do. In such a case, if the energization of the solenoid must be switched from on to off in order to detect disconnection during brake control, it may affect the drive of the pressure-increasing control valve and prevent appropriate brake control from being performed. is there. In addition, if the OFF period is shortened to minimize the influence of brake control, the flyback voltage may be turned ON before it becomes sufficiently large, and accurate disconnection detection of the solenoid may not be performed. is there. Therefore, it is desirable to be able to detect disconnection of the solenoid without switching the transistor from on to off.

  Here, the solenoid is described as an example of the energization target, but the same can be said for the energization circuit that supplies current to the energization target other than the solenoid, and for controlling the on / off of the current to the energization circuit. It is necessary to be able to detect disconnection of the energization circuit with the transistor kept on.

  In view of the above points, the present invention can detect a disconnection of an energization circuit in a state in which the energization circuit is energized in the disconnection detection circuit that detects disconnection of the energization circuit that supplies current to the energization target. The purpose is to do so.

  In order to achieve the above object, according to the first aspect of the present invention, the coil (5) provided between the power source (+ BS) and the energization target (1) and the coil (5) of the energization circuit and the energization target The energization target side potential detection means (6, 6a to 6c) for detecting the energization target side potential which is a potential between (1) and the energization target side potential detection means (6, 6a to 6c). A disconnection detecting means (6d) for detecting that a portion of the energization circuit on the low side from the coil (5) is disconnected when the target-side potential is equal to or higher than a predetermined energization-target-side threshold potential; It is characterized by being.

  In this way, the energization circuit includes the coil (5) for detecting disconnection separately from the energization target (1), and the potential of the portion between the coil (5) and the energization target (1) in the energization circuit is energized. It is detected as a side potential. When the energization target side potential becomes equal to or higher than the energization target side threshold potential, various disconnections in the portion on the low side from the coil (5) are detected. By detecting the disconnection in this manner, it is possible to detect the disconnection of the energization circuit while the energization target (1) is being energized.

  In invention of Claim 2, it is equipped with the power supply side electric potential detection means (6, 6e-6g) which detects the power supply side electric potential which is an electric potential between a power supply (+ BS) and a coil (5) among energization circuits, The disconnection detecting means (6d) is arranged such that when the energization target side potential detected by the energization target side potential detection means (6, 6a to 6c) becomes equal to or higher than the energization target side threshold potential, the power supply side potential detection means (6, 6e to 6g), when the power supply side potential detected by the power supply side is lower than a predetermined power supply side threshold potential, it is detected that a portion of the energization circuit on the low side from the coil (5) is disconnected. .

  Thus, if the power supply side potential is detected in addition to the current supply target side potential, the power supply side potential is less than the predetermined power supply side threshold potential when the current supply target side potential becomes equal to or higher than the current supply target side threshold potential. In this case, it is possible to detect that the portion of the energization circuit on the low side with respect to the coil (5) is disconnected. In this way, even if the inductance L of the coil (5) is reduced, it can be prevented from being recognized as a flyback voltage when power supply noise is generated, and it is possible to prevent erroneous detection that disconnection is detected despite power supply noise. .

  In the invention according to claim 3, the coil (5) is configured by partially forming a printed wiring connecting the power source (+ BS) and the energization target (1) as a coil shape pattern. It is a feature.

  If the coil (5) is configured by the printed wiring in this way, the solder connection with the printed wiring is not required as in the case of the discrete element, and therefore, the disconnection at the bonding portion that occurs when performing the solder bonding or the like. Can be prevented.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

It is a circuit diagram of the energization circuit to which the disconnection detection circuit concerning a 1st embodiment of the present invention was applied. It is a chart showing operation of an energization circuit and a disconnection detection circuit. It is a circuit diagram of the electricity supply circuit to which the disconnection detection circuit concerning 2nd Embodiment of this invention was applied. It is a timing chart showing operation of an energization circuit and a disconnection detection circuit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
A first embodiment of the present invention will be described. In this embodiment, a case where a solenoid provided in a pressure increase control valve for brake control in a vehicle is an energization target will be described as an example, and a disconnection detection circuit for detecting disconnection of the energization target will be described.

  FIG. 1 is a circuit diagram of an energization circuit to which the disconnection detection circuit according to the present embodiment is applied. The energization circuit shown in FIG. 1 controls on / off of energization to the solenoid 1 of the pressure increase control valve, and the disconnection of the solenoid 1 in this energization circuit, for example, the disconnection of the solenoid 1 itself or the location of electrical connection between the solenoid 1 and the wiring. Various disconnections such as disconnection are detected by a disconnection detection circuit.

  The pressure increase control valve is a valve for controlling the pressure increase of each wheel cylinder between the master cylinder and each wheel cylinder, and is configured by a normally open valve, and is in communication according to the energized state of the solenoid 1 And the shut-off state are switched. The pressure increase control valve is in communication because the current supply to the solenoid 1 is turned off during normal braking, and for example, the current supply to the solenoid 1 is turned on during pressure reduction control or holding control in anti-skid control (ABS control). It will be in the interruption state by this. When the solenoid 1 of the pressure increase control valve is disconnected when the wheel is likely to be locked and the wheel cylinder pressure is to be reduced as in the case of the pressure reduction control in the anti-skid control, the pressure increase control valve is in communication and the pressure can be reduced. The wheels will lock and reduce the braking force. For this reason, it is important to take measures against disconnection of the solenoid 1 when the solenoid 1 of the pressure increase control valve is energized. For this reason, in this embodiment, the disconnection detection of the solenoid 1 of such a pressure increase control valve is performed by the disconnection detection circuit.

  As shown in FIG. 1, the energization circuit includes the solenoid 1 of the pressure increase control valve in the power supply line 2 connected to the power supply + BS, thereby applying a voltage from the power supply + BS to the solenoid 1 through the power supply line 2. In this energization circuit, the first transistor 3 constituting the solenoid relay provided on the high side of the solenoid 1 and the second transistor 4 constituting the solenoid driver provided on the low side of the solenoid 1 are controlled to be turned on / off. The energization of the solenoid 1 is switched on and off, and the valve position of the pressure increase control valve is switched based on the energization state of the solenoid 1.

  The first transistor 3 constituting the solenoid relay and the second transistor 4 constituting the solenoid driver are each constituted by a Pch MOSFET and an Nch MOSFET in this embodiment, and are turned on by application of a gate voltage. The first transistor 3 serves as a power switch for the solenoid 1 and is basically turned on. By switching on / off of the second transistor 4, the energization to the solenoid 1 of the pressure increase control valve is switched on / off. It is carried out. For this reason, when the first transistor 3 is turned on and the second transistor 4 is turned off, the energization to the solenoid 1 is turned off, so that the pressure increasing control valve is in a communication state, and the second transistor 4 is turned on. Then, energization to the solenoid 1 is turned on and the pressure increase control valve is cut off.

  Although not shown in FIG. 1, the gate voltages of the first and second transistors 3 and 4 are generated by the gate drive circuit, and the solenoid 1 of the pressure increase control valve for brake control as in this embodiment. When the current is to be energized, the brake ECU serves as a gate drive circuit.

  And the disconnection detection circuit is applied with respect to the electricity supply circuit comprised in this way. Specifically, as shown in FIG. 1, the disconnection detection circuit includes a coil 5 connected between the first transistor 3 and the solenoid 1 of the pressure increase control valve, and a potential between the coil 5 and the solenoid 1. That is, it has a configuration including a detection unit 6 that detects a disconnection by detecting a current to be energized side potential that is a potential on the solenoid 1 side among the potentials at both ends of the coil 5.

  The coil 5 is provided in the power supply line 2 as a separate member from the solenoid 1 to be energized. The coil 5 may be a discrete element. However, a power supply line 2 connecting the power source + BS and the solenoid 1 is formed by a printed wiring in a circuit board, and the printed wiring is partially coiled. It is preferable to form by forming a shape pattern. If the coil 5 is configured by printed wiring in this way, solder connection to the power supply line 2 is not required as in the case of a discrete element, and thus disconnection at a joint portion that occurs when performing solder connection or the like. Can be prevented.

  The detection unit 6 constitutes an energization target side potential detection unit and a disconnection detection unit. In this embodiment, the detection unit 6 includes a Zener diode 6a, an NPN transistor 6b, a resistor 6c, and a microcomputer 6d.

  The Zener diode 6a is connected between the coil 5 and the solenoid 1 with the cathode side facing, and sets the energization target side threshold potential. That is, the Zener breakdown voltage Vz of the Zener diode 6a sets the energization target side threshold potential. The Zener breakdown voltage Vz is set larger than the power source + BS and set smaller than the flyback voltage applied during flyback. The NPN transistor 6b has a base connected to the anode of the Zener diode 6a, a collector connected to the resistor 6c, and an emitter connected to GND. The resistor 6c is connected between the constant voltage source VCC and the collector of the NPN transistor 6b. These Zener diode 6a, NPN transistor 6b, and resistor 6c constitute energization target side potential detecting means in this embodiment. The microcomputer 6d corresponds to a disconnection detecting means, and AD-converts and inputs the potential between the resistor 6c and the NPN transistor 6b. Based on whether the input potential is high level or low level, the energization target side potential is It is determined that the current is equal to or higher than a predetermined energization target side threshold potential, and disconnection of the solenoid 1 is detected. Specifically, the microcomputer 6d can grasp the on / off switching timing of the second transistor 4, and detects the disconnection of the solenoid 1 based on the state of the second transistor 4 and the level of the read voltage value. ing.

  In FIG. 1, the disconnection detection circuit does not show the relationship between the microcomputer 6d and the brake ECU, but the microcomputer 6d and the brake ECU (gate drive circuit) may be configured separately, or the brake ECU is used as the microcomputer 6d. May be. However, when the brake ECU is used as the microcomputer 6d, the state of the second transistor 4 is grasped by itself, so that the microcomputer 6d and the brake ECU are separated from each other as in the case where the microcomputer 6d and the brake ECU are configured separately. On the other hand, the state of the second transistor 4 need not be transmitted.

  As described above, an energization circuit to which the disconnection detection circuit is applied is configured. The operation of the energization circuit having such a configuration and the operation of the disconnection detection circuit applied thereto will be described.

  First, when an ignition switch (not shown) is switched from off to on, a gate voltage is applied to the first transistor 3 through a gate drive circuit such as a brake ECU, and the first transistor 3 is turned on.

  When the brake control such as the initial check for checking the operation of the pressure increase control valve or the anti-skid control is not performed, for example, during normal braking, the brake fluid that is generated in the master cylinder with the pressure increase control valve in the communication state It is assumed that the pressure is transmitted to each wheel cylinder. For this reason, the energization to the solenoid 1 of the pressure increase control valve is turned off. In this case, the energization target side potential between the coil 5 and the solenoid 1 becomes the potential of the power source + BS, and becomes smaller than the zener breakdown voltage Vz of the zener diode 6a. Therefore, the NPN transistor 6b does not turn on because no current flows through the base, and the voltage of the constant voltage source VCC is input to the microcomputer 6d, and the input potential becomes high level.

  Further, at the time of initial check or at the time of pressure reduction control or holding control of anti-skid control, the pressure increase control valve is shut off so that the brake fluid pressure of the master cylinder is not transmitted to the wheel cylinder. For this reason, the second transistor 4 is turned on, and energization to the solenoid 1 of the pressure increase control valve is turned on. In this case, if the voltage drop in the first and second transistors 3 and 4 is ignored, the potential to be energized becomes the voltage obtained by dividing the voltage of the power source + BS by the coil 5 and the solenoid 1, and the Zener diode 6a. Less than the zener breakdown voltage Vz. Therefore, the NPN transistor 6b does not turn on because no current flows through the base, and the voltage of the constant voltage source VCC is input to the microcomputer 6d, and the input potential becomes high level.

  After that, when the second transistor 4 is turned off and the energization of the solenoid 1 is switched from on to off, the current flowing in the coil 5 is interrupted, so that flyback occurs, and the energization target side potential is flyback. The voltage becomes higher than the Zener breakdown voltage Vz of the Zener diode 6a. As a result, the NPN transistor 6b is turned on with a current flowing through the base, and the on-voltage of the NPN transistor 6b is input to the microcomputer 6d, and the input potential becomes low level. When the flyback is settled, the energization target side potential becomes the potential of the power source + BS again and becomes smaller than the zener breakdown voltage Vz of the zener diode 6a, so that the NPN transistor 6b is turned off and the input potential of the microcomputer 6d returns to the high level. .

  On the other hand, if the solenoid 1 is disconnected while the solenoid 1 is energized, the second transistor 4 is turned on since the second transistor 4 is switched from on to off. In spite of this, the energization of the coil 5 is cut off and flyback occurs. For this reason, when the flyback is settled after the input voltage of the microcomputer 6d instantaneously becomes low level, it returns to high level again. Therefore, the microcomputer 6d detects that the solenoid 1 is disconnected when the input potential changes to a low level while the second transistor 4 is turned on.

  FIG. 2 is a chart summarizing the above operations. As shown in this figure, if the input potential of the microcomputer 6d is at a high level (Hi) when the second transistor 4 is on, no disconnection has occurred and it is normal. When the second transistor 4 is switched from on to off, the input potential of the microcomputer 6d changes to low level (Low) and then returns to high level. When the input potential of the microcomputer 6d returns to a high level after the second transistor 4 is turned on and then returns to a high level, a disconnection has occurred and an abnormality is detected.

  As described above, in the disconnection detection circuit applied to the energization circuit of this embodiment, the energization circuit includes the coil 5 for detecting disconnection separately from the solenoid 1 to be energized, and the coil 5 in the energization circuit is energized. The potential of the portion between the target solenoids 1 is detected as the energization target side potential. When the energization target side potential becomes equal to or higher than the energization target side threshold potential, the disconnection of the solenoid 1 and various disconnections of the portion on the low side from the coil 5 are detected.

  By detecting the disconnection in this manner, it is possible to detect the disconnection of the energization circuit while the second transistor 4 for energizing the solenoid 1 is kept on. Since the disconnection can be detected with the second transistor 4 turned on, the disconnection cannot be detected unless the second transistor 4 is switched off, so that the drive of the pressure increase control valve is not affected.

  As a disconnection detection circuit for detecting disconnection of the solenoid 1, a disconnection detection resistor is provided on the low side of the solenoid 1, and it is determined whether or not current is flowing through the energization circuit based on the voltage across the disconnection detection resistor. However, it is possible to detect disconnection. However, in such a disconnection detection circuit, a monitor circuit for monitoring each voltage across the disconnection detection resistor is required, and the number of parts increases. Also from this point, it is possible to reduce the increase in the number of parts by adopting a configuration in which disconnection detection can be performed based only on the energization target side potential as in this embodiment.

(Second Embodiment)
A second embodiment of the present invention will be described. In this embodiment, the configuration of the disconnection detection circuit is changed so that the inductance L of the coil 5 can be reduced compared to the first embodiment, and the rest is the same as in the first embodiment. Therefore, only a different part from 1st Embodiment is demonstrated.

  In the first embodiment, the disconnection detection circuit including the coil 5 and the detection circuit 6 detects the disconnection of the solenoid 1, more specifically, the disconnection on the lower side than the coil 5. However, since the coil 5 is provided separately from the solenoid 1 to be energized in the energization circuit, it is preferable to make the inductance L of the coil 5 as small as possible from the viewpoint of improving the energization controllability of the solenoid 1. On the other hand, it is preferable that the inductance L of the coil 5 is large from the viewpoint of enabling accurate disconnection detection. That is, as the inductance L of the coil 5 is reduced, the flyback voltage generated when the solenoid 1 is disconnected is reduced. Therefore, the energization target side threshold potential must be set to be small accordingly. It is recognized as a back voltage, and there is a concern about erroneous detection that disconnection is detected even though the power supply noise. Therefore, in the present embodiment, the erroneous detection that the disconnection is detected at the time of power supply noise is prevented while reducing the inductance L of the coil 5.

  FIG. 3 is a circuit diagram of an energization circuit to which the disconnection detection circuit according to the present embodiment is applied. As shown in this figure, in this embodiment, the detection unit 6 also detects the potential between the first transistor 3 and the coil 5, that is, the power supply side potential with respect to the coil 5. The detection unit 6 of the present embodiment includes a Zener diode 6e, an NPN transistor 6f, and a resistor 6g having the same configuration as the Zener diode 6a, the NPN transistor 6b, and the resistor 6c described in the first embodiment.

  The zener diode 6e is connected between the first transistor 3 and the coil 5 with the cathode side facing, and sets the threshold potential of the power supply side potential. That is, the Zener breakdown voltage Vz of the Zener diode 6e sets the threshold potential. For example, the Zener breakdown voltage Vz is made equal to the Zener breakdown voltage Vz of the Zener diode 6a. The NPN transistor 6f has a base connected to the anode of the Zener diode 6e, a collector connected to the resistor 6g, and an emitter connected to GND. The resistor 6g is connected between the constant voltage source VCC and the collector of the NPN transistor 6f. The potential between the resistor 6g and the NPN transistor 6f is AD-converted and input to the microcomputer 6d. In the present embodiment, the Zener diode 6e, the NPN transistor 6f, and the resistor 6g constitute a power supply side potential detecting means.

  Thus, the energization circuit to which the disconnection detection circuit according to the present embodiment is applied is configured. The operation of the energization circuit having such a configuration and the operation of the disconnection detection circuit applied thereto will be described.

  In the present embodiment, disconnection detection is performed based on the on / off state of the second transistor 4, the power supply side potential on the high side of the coil 5, and the level of the current supply side potential on the low side.

  First, when an ignition switch (not shown) is switched from off to on, a gate voltage is applied to the first transistor 3 through a gate drive circuit such as a brake ECU, and the first transistor 3 is turned on.

  When the brake control such as the initial check for checking the operation of the pressure increase control valve or the anti-skid control is not performed, for example, during normal braking, the brake fluid that is generated in the master cylinder with the pressure increase control valve in the communication state It is assumed that the pressure is transmitted to each wheel cylinder. For this reason, the energization to the solenoid 1 of the pressure increase control valve is turned off. In this case, the power supply side potential on the high side of the coil 5 and the energization target side potential on the low side are both the potential of the power supply + BS, and are smaller than the Zener breakdown voltage Vz of the Zener diodes 6a and 6e. Therefore, the NPN transistors 6b and 6f do not turn on because no current flows through the base, and the microcomputer 6d has the voltage of the constant voltage source VCC as a potential between the resistor 6c and the NPN transistor 6b (hereinafter referred to as a first input potential). Is input, and the voltage of the constant voltage source VCC is input as a potential between the resistor 6g and the NPN transistor 6f (hereinafter referred to as a second input potential). That is, both the first and second input potentials are at a high level.

  Further, at the time of initial check or at the time of pressure reduction control or holding control of anti-skid control, the pressure increase control valve is shut off so that the brake fluid pressure of the master cylinder is not transmitted to the wheel cylinder. For this reason, energization to the solenoid 1 of the pressure increase control valve is turned on. In this case, ignoring the voltage drop in the first and second transistors 3 and 4, the power supply side potential is the voltage of the power supply + BS, and the energization target side potential is the voltage of the power supply + BS by the coil 5 and the solenoid 1. The voltage is divided. Therefore, both the power supply side potential and the energization target side potential are smaller than the Zener breakdown voltage Vz of the Zener diodes 6a and 6e. Therefore, the NPN transistors 6b and 6f do not turn on because no current flows through the base, and the microcomputer 6d receives the voltage of the constant voltage source VCC as the first and second input potentials, and the input potential becomes high level.

  Thereafter, when the energization of the solenoid 1 is switched from on to off, the current flowing in the coil 5 is cut off, so that flyback occurs, the energization target side potential becomes the flyback voltage, and the zener of the zener diode 6a. It becomes larger than the breakdown voltage Vz. However, since the power supply side potential is not affected by the flyback voltage, it remains smaller than the Zener breakdown voltage Vz of the Zener diode 6e. Therefore, the NPN transistor 6b is turned on with a current flowing on the base, and the NPN transistor 6f is turned off without flowing a current on the base. Therefore, the microcomputer 6d has the ON voltage of the NPN transistor 6b as the first input potential. And the voltage of the constant voltage source VCC is input as the second input potential. Therefore, the first input potential is at a low level and the second input potential is at a high level. When the flyback is settled, the energization target side potential becomes the potential of the power source + BS again and becomes smaller than the zener breakdown voltage Vz of the zener diode 6a, so that the NPN transistor 6b is turned off and the first input potential inputted to the microcomputer 6d. Return to high level.

  On the other hand, if the solenoid 1 is disconnected while the solenoid 1 is energized, the second transistor 4 is turned on since the second transistor 4 is switched from on to off. In spite of this, the energization of the coil 5 is cut off and flyback occurs. Therefore, the second input potential among the input potentials of the microcomputer 6d is in a high level state, and the first input potential is instantaneously lowered to low level and then returned to the high level again when the flyback is settled. Therefore, the microcomputer 6d detects that the solenoid 1 is disconnected when the first input potential changes to a low level while the second transistor 4 is turned on.

  When power noise is superimposed on the power supply line 2 when both the first and second transistors 3 and 4 are on, the power noise is superimposed on both the high side and the low side of the coil 5. Appears as an in-phase potential level increase. For this reason, when the power supply noise is large and the potential to be energized exceeds the Zener breakdown voltage Vz of the Zener diode 6a, the power supply side potential also exceeds the Zener breakdown voltage Vz of the Zener diode 6e, and is input to the microcomputer 6d. First, the second input potential is simultaneously at a low level. Therefore, even if the first input potential becomes low level when the second transistor 4 is turned on, the disconnection and detection of the solenoid 1 is detected only when the second input potential is high level at that time. If the second input potential is at a low level, the disconnection of the solenoid 1 is not detected.

  FIG. 4 is a timing chart showing the above operation. As shown in this figure, when the second transistor 4 is turned off to turn off the energization of the solenoid 1, the second input potential is at a high level but the first input potential is at a low level. At the time of disconnection, the second transistor 4 is turned on, but the first input potential is at a low level. In this case, a disconnection occurs and an abnormality is detected. When power supply noise occurs, both the first and second input potentials are at a low level when the second transistor 4 is turned on. In this case, since it is a power supply noise rather than a disconnection, it is not detected as a disconnection.

  Thus, if the power supply side potential is detected in addition to the current supply target side potential, the power supply side potential is less than the predetermined power supply side threshold potential when the current supply target side potential becomes equal to or higher than the current supply target side threshold potential. In this case, it is possible to detect that the portion of the energization circuit on the low side with respect to the coil 5 is disconnected. In this way, even if the inductance L of the coil 5 is reduced, it can be prevented from being recognized as a flyback voltage when power supply noise is generated, and a false detection that a disconnection is detected even though the power supply noise is generated. Can be prevented.

(Other embodiments)
In each of the above embodiments, the solenoid is described as an example of the energization target. However, the disconnection detection circuit can also be applied to an energization circuit that supplies current to an energization target other than the solenoid.

  DESCRIPTION OF SYMBOLS 1 ... Solenoid of a pressure increase control valve, 2 ... Power supply line 3, 4 ... 1st, 2nd transistor, 5 ... Coil, 6 ... Detection part, 6a, 6e ... Zener diode, 6b, 6f ... NPN transistor, 6c , 6g ... resistor, 6d ... microcomputer

Claims (3)

In a disconnection detection circuit that is connected to a power source (+ BS) and is applied to an energization circuit that supplies current to the energization target (1) and detects disconnection of the energization circuit.
A coil (5) provided between the power source (+ BS) and the energization target (1);
An energization target side potential detecting means (6, 6a to 6c) for detecting an energization target side potential which is a potential between the coil (5) and the energization target (1) in the energization circuit;
When the energization target side potential detected by the energization target side potential detection means (6, 6a to 6c) is equal to or higher than a predetermined energization target side threshold potential, the coil (5) of the energization circuit is more than the coil (5). A disconnection detection circuit comprising: disconnection detection means (6d) for detecting that the low-side portion is disconnected. Power supply side potential detection means (6, 6e-6g) for detecting a power supply side potential which is a potential between the power supply (+ BS) and the coil (5) in the energization circuit,
The disconnection detecting means (6d) is configured to detect the power supply side potential when the current supply target side potential detected by the current supply target side potential detection means (6, 6a to 6c) becomes equal to or higher than the current supply target side threshold potential. When the power supply side potential detected by the detection means (6, 6e to 6g) is less than a predetermined power supply side threshold potential, a portion on the low side of the coil (5) in the energization circuit is disconnected. The disconnection detection circuit according to claim 1, wherein:   The said coil (5) is comprised by making the printed wiring which connects between the said power supply (+ BS) and the said electricity supply object (1) into a coil shape pattern partially. Or the disconnection detection circuit of 2.

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