JP2016122544A - Relay drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the electric coil of a relay from being brought into electrification state continuously over a long time, even when a component of semiconductor fails.SOLUTION: In an electrification path where the coil current i21 of the electric coil 21 of a relay 20 flows, two switching elements 11A, 12A are arranged in series connection, and electrification is controlled by performing on/off control of two switching elements 11A, 12A simultaneously by means of a CPU14. Since two switching elements 11A, 12A never fail simultaneously, the coil current i21 can be cut off reliably, and long time continuous electrification can be blocked. Consequently, fuming and firing incident to abnormal temperature rise are prevented. Furthermore, a function for automatically diagnosing the failure is provided, and notifies of occurrence of failure.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a relay drive circuit for driving various relays mounted on a vehicle or the like, and more particularly to a technique for safety measures.

  For example, in order to switch on / off of power supply to a load such as an electric motor, a mechanical relay is generally used. That is, the connection between the power source and the ground and the load is controlled to open and close using the switch contact of the relay. The mechanical relay can switch the open / close state of the switch contact by moving the movable part by switching between energization / non-energization of the electric coil. In order to switch between energization / non-energization of the electric coil of such a relay, a relay drive circuit is used.

  For example, Patent Literature 1 to Patent Literature 5 are known as related arts of such a relay drive circuit.

  Patent Document 1 shows a technique related to a relay drive circuit capable of reducing power consumption. Specifically, a plurality of switching elements are connected in series to an electrical coil of a relay, and the timing for driving the plurality of switching elements is controlled so as to be shifted from each other using a delay unit.

  Patent Document 2 shows a technique for preventing noise from being generated while suppressing self-heating due to a coil current in a relay drive circuit. Specifically, the magnitude of the current flowing through the electrical coil of the relay is adjusted using a variable voltage regulator or by PWM control of the current.

  Patent Document 3 is a vehicle power supply device that controls an ignition power supply, in order to keep the ignition power supply on even when the IG relay driving system is disconnected or at a low voltage, and to prevent burnout of a printed circuit board or the like due to overcurrent. Shows the technology.

  Patent Document 4 shows a technique related to a relay driving device that suppresses heat generation of a relay. Specifically, a voltage stabilization circuit using a Zener diode is used to adjust the output voltage of the transistor 156 so that the voltage applied to the electrical coil of the relay is kept at a predetermined value.

  Patent Document 5 shows a technique related to a relay drive circuit that can maintain the state of the relay even when the voltage of the drive power supply decreases after the relay is turned on, and can save power. Specifically, the first switch 7 for operating the relay contact and the second switch for maintaining the operation state of the relay contact are connected in parallel to the relay coil 3, and the applied voltage drops below the threshold value. When this happens, the first switch is controlled to turn on.

JP 2010-251200 A JP 2011-216229 A JP 2012-183901 A JP 2013-171773 A JP 2014-116197 A

  By the way, for example, an electric motor that drives various electrical devices (for example, a power window) mounted on a vehicle tends to require a relatively large power supply current. Therefore, a relay used for controlling the energization of such a load is required to be able to switch a large-capacity power supply current at the contact.

  Therefore, for relays used for such control, the resistance value of the electric coil built in the relay is reduced to flow a large current, the suction force for moving the movable part of the relay is increased, and the switch contact is Considered to open and close securely.

  However, when a large current is passed through the electric coil built in the relay, a large amount of heat is generated in the electric coil, and it is inevitable that the temperature rises rapidly. If such a temperature rise exceeds the allowable range of heat resistance, the coating of the electric coil may be deteriorated or broken, and a circuit may be dead short due to poor insulation. Further, in such a case, it is assumed that smoke or ignition occurs in the worst case. Further, when the heat resistance of the relay is increased, there is a high possibility that the relay will be enlarged and the cost of parts will increase.

  Therefore, an upper limit (for example, a maximum of 1 minute) of the continuous energization time of the electric coil may be defined for the relay used for energization control of loads of various electrical equipment. For this reason, when energizing the electrical coil of the relay, it is necessary to control so that the continuous energization time does not become long. For example, in the case of a load such as an electric motor for driving a power window, it is not necessary to energize continuously for a long time in reality. Normally, the energized state does not occur.

  However, for example, when a failure (fixed in the ON state) occurs in a switching element (for example, a transistor) that is a component of a relay drive circuit, there is a possibility that energization of the relay's electric coil may be continued for a long time. Is also possible. Moreover, it is inevitable that a failure of a component such as a semiconductor occurs with a certain probability. In the case of such a failure, it is possible to detect the failure. However, even if a failure is detected, there is a case where energization of the relay electric coil cannot actually be interrupted, so there is a concern that the heat generation of the relay electric coil may cause smoke or ignition.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to continuously energize an electric coil of a relay for a long time even when a failure of a component such as a semiconductor occurs. It is an object of the present invention to provide a relay drive circuit capable of preventing the above-described problem.

In order to achieve the above-described object, a relay drive circuit according to the present invention is characterized by the following (1) to (5).
(1) a relay including an electric coil having restrictions on continuous energization time;
A first switching element disposed in an energization path of the electric coil of the relay;
A second switching element disposed in the energization path in series with the first switching element;
When the electric coil is energized, both the first switching element and the second switching element are controlled to be on, and when the electric coil is de-energized, the first switching element and An energization control unit that switches both of the second switching elements to an off state;
It is provided with.
(2) The relay drive circuit according to (1) above,
Each of the first switching element and the second switching element is a semiconductor switch having a control input terminal, and has a different type of configuration.
It is characterized by that.
(3) The relay drive circuit according to (2) above,
The second switching element is connected to a higher potential side than the first switching element;
A third switching element for controlling a potential of a control input terminal of the second switching element;
It is provided with.
(4) The relay drive circuit according to (3) above,
A plurality of the first switching elements and the second switching elements,
An output terminal of the third switching element is commonly connected to a plurality of control input terminals of the second switching element;
It is characterized by that.
(5) The relay drive circuit according to any one of (1) to (4) above,
A fault monitoring unit for monitoring the potential between the first switching element and the second switching element and identifying the presence or absence of a fault when at least the electric coil is in a non-energized state;
It is provided with.

According to the relay drive circuit having the configuration of (1), the energization of the electric coil of the relay is turned on / off by the series circuit of the first switching element and the second switching element, so that the first switching Even when one of the element and the second switching element breaks down, if the other is controlled to be off, energization of the electric coil can be reliably interrupted. Therefore, it is possible to prevent the continuous energization time of the electric coil from exceeding a specified value, and to prevent smoke and ignition due to heat generation. In addition, since it is impossible in a normal environment for the two switching elements to fail at the same time, it is possible to reliably prevent smoke and fire due to heat generated by the electric coil. Further, smoke and fire can be prevented without increasing the heat resistance performance of the electric coil, so that an increase in the size of relays and an increase in parts cost can be avoided.
According to the relay drive circuit having the configuration (2), since the semiconductor switch is used, it is possible to prevent an increase in the number of movable parts and electrical contacts, thereby improving reliability. Further, by adopting semiconductor switches of different types as the first switching element and the second switching element, a reliable switching operation is possible even when they are connected in series.
According to the relay drive circuit having the configuration (3), the second switching element can be reliably switched on and off by controlling the third switching element.
According to the relay drive circuit having the configuration (4), a plurality of the first switching elements and the second switching elements are provided, whereby a plurality of relays can be controlled. In addition, a plurality of relays can be controlled without increasing the number of the third switching elements.
According to the relay drive circuit having the configuration of (5) above, when a failure state occurs in which one of the first switching element and the second switching element is fixed in the on state, the failure occurs. Can be detected. Therefore, it is possible to prevent the device from being left in a state where a failure has occurred and to prompt the implementation of repairs before the remaining normal switching elements fail, thereby preventing smoke and fire.

  According to the relay drive circuit of the present invention, it is possible to prevent the electrical coil of the relay from being continuously energized for a long time even when a failure of a component such as a semiconductor occurs. Therefore, even when a relay including an electric coil having a restriction on the continuous energization time is employed, it is possible to avoid the occurrence of smoke or ignition at the time of failure.

  The present invention has been briefly described above. Further, the details of the present invention will be further clarified by reading through a mode for carrying out the invention described below (hereinafter referred to as “embodiment”) with reference to the accompanying drawings. .

FIG. 1 is an electric circuit diagram illustrating a configuration of a main part of an in-vehicle electrical device including the relay drive circuit according to the first embodiment. FIG. 2 is a time chart showing an operation example of the relay drive circuit shown in FIG. FIG. 3 is an electric circuit diagram illustrating a configuration of a main part of the in-vehicle electrical device including the relay drive circuit according to the second embodiment. FIG. 4 is a flowchart showing a diagnostic operation in the relay drive circuit shown in FIG. FIG. 5 is an electric circuit diagram showing a configuration of a main part of the in-vehicle electrical device including the relay drive circuit of the third embodiment.

  Specific embodiments relating to the relay drive circuit of the present invention will be described below with reference to the drawings.

<First Embodiment>
A configuration example of a main part of the in-vehicle electrical device 100 including the relay drive circuit 10 of the first embodiment is shown in FIG.

<Overview>
As a specific example of the on-vehicle electrical device 100 shown in FIG. 1, a power window device can be assumed. Such an in-vehicle electrical device 100 needs to pass a relatively large current to the DC electric motor 30 that is a driving source in order to smoothly and quickly move a moving part having a large weight such as a window glass.

  In addition, regarding the relay 20 used for controlling the energization / non-energization of the DC electric motor 30 of the in-vehicle electrical device 100, it is necessary to reliably switch on and off a large current (switching of the contact) with the switches 23 and 24. It is necessary to use electric coils 21 and 22 having a small value. Therefore, a large current flows through the electric coils 21 and 22 of the relay 20, and the amount of heat generated by the electric coils 21 and 22 also increases. Further, when the electric coils 21 and 22 are continuously energized for a long time, a significant temperature increase occurs in the coils, and there is a possibility that smoke and fire may occur at the same time as the insulation coating is broken. Therefore, in the case of the relay 20 that does not have a particularly high heat resistance, an upper limit value (for example, 1 minute) of the continuous energization time of the electric coils 21 and 22 is defined in advance.

  Therefore, regarding the operation of the relay drive circuit 10, it is necessary to consider that the continuous energization time of the electric coils 21 and 22 does not exceed the specified value. However, in a general relay drive circuit, there is a possibility that an unexpected operation may be performed when an internal component fails. For example, even when the electric coils 21 and 22 are controlled to be de-energized, Actually, there is a possibility that a current flows through the electric coils 21 and 22 continuously. In the relay drive circuit 10 shown in FIG. 1, special measures are taken so that the continuous energization time of the electric coils 21 and 22 does not exceed a specified value even when a component failure occurs.

<Detailed description of configuration>
<Description of Relay 20 and DC Electric Motor 30>
The relay 20 shown in FIG. 1 has two sets of relays that operate independently of each other. That is, one relay is composed of the electric coil 21 and the switch 23, and the other relay is composed of the electric coil 22 and the switch 24. That is, when the electric coil 21 is energized / de-energized, the movable part of the switch 23 moves and the electric contact is switched. In addition, when the switch 23 is energized / de-energized, the movable part of the switch 24 moves and the electrical contact is switched.

  The relay 20 is provided in order to switch on and off the energization of the DC electric motor 30 and the energization direction. In the state shown in FIG. 1, that is, when both the switches 23 and 24 are off, the terminal 31 of the DC electric motor 30 is connected to the ground line 41 (4) via the connection terminal 45 and the switch 23, and the terminal 32 is also The motor current i30 does not flow because it is connected to the ground line 41 (4) via the connection terminal 46 and the switch 24.

  On the other hand, when the switch 23 of the relay 20 is on and the switch 24 is off, the switch 23, the connection terminal 45, the terminal 31, the DC electric motor 30, and the terminal 32 are supplied from the power line (for example, supplying + 12V voltage) 40. A path for the motor current i30 to flow through the connection terminal 46 and the switch 24 to the ground line 41 (4) is formed.

  When the switch 23 is off and the switch 24 is on, the power line 40 is grounded through the switch 24, connection terminal 46, terminal 32, DC electric motor 30, terminal 31, connection terminal 45, and switch 23. A path for the motor current i30 in the reverse direction to flow through the line 41 (4) is formed.

  One electric coil 21 of the relay 20 has a high-potential side terminal connected to the power supply line 40 via a diode D3, and a low-potential side terminal connected to the connection terminal 17A of the relay drive circuit 10 output. The other electric coil 22 of the relay 20 has a high-potential side terminal connected to the power supply line 40 via a diode D3, and a low-potential side terminal connected to the connection terminal 17B of the relay drive circuit 10 output. .

  Therefore, by controlling the potential of the connection terminal 17A of the relay drive circuit 10 output, it is possible to switch between energization / non-energization of the electric coil 22 of the relay 20 and by controlling the potential of the connection terminal 17B. Can be switched between energization / non-energization.

<Configuration of Relay Drive Circuit 10>
1 includes a switching element 11A and 11B, a switching element 12A and 12B, a switching element 13, a microcomputer (CPU) 14, resistors R11 to R16, resistors R21 to R24, and diodes D1 and D2. It has.

  The switching element 11A and the switching element 12A arranged on the upper side are circuits for controlling the potential of the connection terminal 17A, and are connected in series to the path of the coil current i21. The switching element 11B and the switching element 12B arranged on the lower side are circuits for controlling the potential of the connection terminal 17B, and are connected in series to the path of the coil current i22. The switching element 13 is a switch for commonly controlling on / off of the upper switching element 12A and the lower switching element 12B.

  In the relay drive circuit 10 shown in FIG. 1, N-channel MOSFETs (field effect transistors) are employed as the switching elements 11A and 11B so as to facilitate reliable switching. Further, PNP type transistors are employed as the switching elements 12A and 12B, and NPN type transistors are employed as the switching element 13.

  The microcomputer 14 implements a control function required for the in-vehicle electrical device 100 by executing a program incorporated in advance. For example, each output port 14a, 14b, and 14c is output in accordance with a “forward rotation instruction signal” and a “reverse rotation instruction signal” output from an output of a host electronic control unit (ECU) (not shown) or by a button operable by the user. Control signals SGA, SGB, and SGC, respectively.

  The control signal SGA is a signal for switching on and off the switching element 11A, and is applied from the output port 14a to the gate control terminal 11Ag of the switching element 11A via the resistor R12. The control signal SGB is a signal for switching on / off of the switching element 11B, and is applied from the output port 14b to the gate control terminal 11Bg of the switching element 11B via the resistor R22. The control signal SGC is a signal for turning on and off the switching element 13 and the switching elements 12A and 12B, and is applied from the output port 14c to the base control terminal of the switching element 13 via the resistor R16.

  The switching element 11A has a source terminal 11As connected to the ground line 41 (1) and a drain terminal 11Ad connected to the collector terminal 12Ac of the switching element 12A via a wiring 16A. Similarly, the switching element 11B has a source terminal connected to the ground line 41 (2) and a drain terminal connected to the collector terminal of the switching element 12B via the wiring 16B.

  The base terminal 12Ab of the switching element 12A is connected to the collector terminal of the switching element 13 via the resistor R14. Similarly, the base control terminal of the switching element 12B is also connected to the collector terminal of the switching element 13 via the resistor R24.

  A resistor R13 is connected between the base terminal 12Ab and the emitter terminal 12Ae of the switching element 12A, and the emitter terminal 12Ae is connected to the connection terminal 17A via the wiring 15A. Similarly, a resistor R23 is connected between the base control terminal and the emitter terminal of the switching element 12B, and the emitter terminal is connected to the connection terminal 17B via the wiring 15B.

  The path of the coil current i21 flowing through the electric coil 21 of the relay 20 is as follows. That is, from the power supply line 40, the ground line 41 passes through the diode D3, the electric coil 21, the connection terminal 17A, the wiring 15A, the switching element 12A (between the emitter and the collector), the wiring 16A, and the switching element 11A (between the drain and source). Current flows through (1). However, when at least one of the switching element 11A and the switching element 12A is off, the coil current i21 is cut off.

  The path of the coil current i22 flowing through the electric coil 22 of the relay 20 is as follows. That is, from the power supply line 40, the ground line 41 passes through the diode D3, the electric coil 22, the connection terminal 17B, the wiring 15B, the switching element 12B (between the emitter and the collector), the wiring 16B, and the switching element 11B (between the drain and source). Current flows through (2). However, when at least one of the switching element 11B and the switching element 12B is off, the coil current i22 is cut off.

<Description of operation>
FIG. 2 shows an operation example of the relay drive circuit 10 shown in FIG.
<Initial state and stop state>
The control signals SGA, SGB, and SGC output from the microcomputer 14 to the output ports 14a to 14c are all turned off (low level: voltage close to the ground potential) in the initial state. The same applies to the stop state.

  When the control signal SGA is off, the potential difference between the gate control terminal 11Ag and the source terminal 11As of the switching element 11A is small, and the drain terminal 11Ad and the source terminal 11As of the switching element 11A are non-conductive (off). Become. Similarly, when the control signal SGB is off, the potential difference between the gate control terminal and the source terminal of the switching element 11B becomes small, and the drain terminal and the source terminal of the switching element 11B become non-conductive (off). .

  Further, when the control signal SGC is OFF, the potential difference between the base control terminal 13b and the emitter terminal 13e of the switching element 13 is reduced, and the collector terminal 13c and the emitter terminal 13e of the switching element 13 are not conductive (OFF). )become. Since the switching element 13 is off, both the switching elements 12A and 12B are off. That is, since no current flows through the resistors R13 and R14, the potential difference between the emitter terminal 12Ae and the base terminal 12Ab of the switching element 12A is reduced, and the switching element 12A is turned off. Similarly, since no current flows through the resistors R23 and R24, the potential difference between the emitter terminal and the base terminal of the switching element 12B is reduced, and the switching element 12B is turned off.

  In the above state, the path through which the coil current i21 flows is blocked by the switching element 11A and also by the switching element 12A. Further, the path through which the coil current i22 flows is blocked by the switching element 11B, and is also blocked by the switching element 12B.

  That is, since the coil current i21 does not flow to the electric coil 21, this relay is off, and the switch 23 maintains the state shown in FIG. Further, since the coil current i22 does not flow to the electric coil 22, this relay is also turned off, and the switch 24 maintains the state shown in FIG. Therefore, the motor current i30 does not flow through the DC electric motor 30, and the DC electric motor 30 is stopped.

<Driving in forward direction>
For example, when the driver operates any button to open the vehicle window (power window), the “forward rotation instruction signal” applied to the microcomputer 14 is temporarily turned on (section T21 in FIG. 2). Become.

  When the “forward rotation instruction signal” is turned on, the microcomputer 14 switches the control signal SGA from OFF to ON, and simultaneously switches the control signal SGC from OFF to ON. The control signal SGB is kept off.

  When the control signal SGA is on, the potential difference between the gate control terminal 11Ag and the source terminal 11As of the switching element 11A is equal to or greater than the threshold value, and the drain terminal 11Ad and the source terminal 11As of the switching element 11A are conductive (on). Switch to state.

  Further, when the control signal SGC is on, the potential difference between the base control terminal 13b and the emitter terminal 13e of the switching element 13 is equal to or greater than the threshold value, so that the collector terminal 13c and the emitter terminal 13e of the switching element 13 are electrically connected. Switch to the (On) state.

  Since the switching element 13 is on, both the switching elements 12A and 12B are turned on. That is, since current flows through the resistors R13 and R14, the potential difference between the emitter terminal 12Ae and the base terminal 12Ab of the switching element 12A becomes equal to or greater than the threshold value, and the switching element 12A is turned on. Similarly, since a current also flows through the resistors R23 and R24, the potential difference between the emitter terminal and the base terminal of the switching element 12B becomes equal to or greater than the threshold value, and the switching element 12B is turned on.

  In the above state, since the switching element 11A is on and the switching element 12A is on, a path for flowing the coil current i21 is formed. That is, from the power supply line 40, the ground line 41 passes through the diode D3, the electric coil 21, the connection terminal 17A, the wiring 15A, the switching element 12A (between the emitter and the collector), the wiring 16A, and the switching element 11A (between the drain and source). Current flows through (1). In addition, although the switching element 12B is turned on, the path for flowing the coil current i22 remains cut off because the switching element 11B maintains the off state.

  That is, the coil current i21 flows through the electric coil 21, the relay (upper side of the 20) is turned on, and the connection state of the switch 23 is switched. As a result, the motor current i30 flows from the power supply line 40 through the switch 23, the connection terminal 45, the terminal 31, the DC electric motor 30, the terminal 32, the connection terminal 46, and the switch 24 to the ground line 41 (4). That is, since the motor current i30 flows in the forward direction, the DC electric motor 30 is driven in the forward rotation direction.

  When the section of T21 shown in FIG. 2 ends and the “normal rotation instruction signal” is switched off, the control signals SGA and SGC are switched off again. As a result, the switching element 11A and the switching elements 12A and 12B are switched off, and the path of the coil current i21 is interrupted again. Accordingly, the driving of the DC electric motor 30 is stopped.

  As shown in FIG. 2, the length of the section T21B through which the coil current i21 flows is usually equal to the section T21 of the “forward rotation instruction signal” (the case of failure will be described later). Therefore, a state in which the coil current i21 continues to flow through the electric coil 21 for a long time does not occur.

<Driving in reverse direction>
For example, when the driver operates any button to close the vehicle window (power window), the “reverse rotation instruction signal” applied to the microcomputer 14 is temporarily turned on (section T22 in FIG. 2). .

  When the “reverse rotation instruction signal” is turned on, the microcomputer 14 switches the control signal SGB from off to on, and simultaneously switches the control signal SGC from off to on. The control signal SGA remains off.

  When the control signal SGB is on, the potential difference between the gate control terminal and the source terminal of the switching element 11B is equal to or greater than the threshold value, and the drain terminal and the source terminal of the switching element 11B are switched to a conductive (on) state.

  Further, when the control signal SGC is on, the potential difference between the base control terminal 13b and the emitter terminal 13e of the switching element 13 is equal to or greater than the threshold value, so that the collector terminal 13c and the emitter terminal 13e of the switching element 13 are electrically connected. Switch to the (On) state.

  Since the switching element 13 is on, both the switching elements 12A and 12B are turned on. That is, since current flows through the resistors R13 and R14, the potential difference between the emitter terminal 12Ae and the base terminal 12Ab of the switching element 12A becomes equal to or greater than the threshold value, and the switching element 12A is turned on. Similarly, since a current also flows through the resistors R23 and R24, the potential difference between the emitter terminal and the base terminal of the switching element 12B becomes equal to or greater than the threshold value, and the switching element 12B is turned on.

  In the above state, since the switching element 11B is on and the switching element 12B is on, a path for flowing the coil current i22 is formed. That is, from the power supply line 40, the ground line 41 passes through the diode D3, the electric coil 22, the connection terminal 17B, the wiring 15B, the switching element 12B (between the emitter and the collector), the wiring 16B, and the switching element 11B (between the drain and source). Current flows through (2). In addition, although the switching element 12A is turned on, since the switching element 11A maintains the off state, the path for passing the coil current i21 remains blocked.

  That is, the coil current i <b> 22 flows through the electric coil 22, the relay (under 20) is turned on, and the connection state of the switch 24 is switched. As a result, the motor current i30 flows from the power line 40 through the switch 24, the connection terminal 46, the terminal 32, the DC electric motor 30, the terminal 31, the connection terminal 45, and the switch 23 to the ground line 41 (4). That is, since the motor current i30 flows in the reverse direction, the DC electric motor 30 is driven in the reverse direction.

  When the section of T22 shown in FIG. 2 ends and the “reverse rotation instruction signal” is switched off, the control signals SGB and SGC are switched off again. Thereby, the switching element 11B and the switching element 12B are switched off, respectively, and the path of the coil current i22 is interrupted again. Accordingly, the driving of the DC electric motor 30 is stopped.

  As shown in FIG. 2, the length of the section T22B through which the coil current i22 flows is normally equal to the section T22 of the “reverse rotation instruction signal” (the case of failure will be described later). Therefore, a state in which the coil current i22 continues to flow through the electric coil 22 for a long time does not occur.

<Operation when a failure occurs>
Various parts may fail in rare cases. For example, since each of the switching elements 11A, 11B, 12A, and 12B in FIG. 1 is a semiconductor switch, there is a possibility of deterioration and failure. As a specific example, there may be a case where the state between the drain (11Ad) and the source (source terminal 11As) of the switching element 11A is fixed in a conductive state (short circuit). Further, there may be a case where the state between the emitter (12Ae) and the collector (collector terminal 12Ac) of the switching element 12A is fixed while being in a conductive state (short circuit). The same applies to the switching elements 11B and 12B.

  The failure of the switching element 11A and the failure of the switching element 12A as described above affect the path through which the coil current i21 flows. If the coil current i21 does not change while flowing, an abnormal temperature rise due to heat generation of the electric coil 21 may destroy the coating of the electric coil 21 and cause smoke or ignition. In addition, if the coil current i22 does not change while flowing, an abnormal temperature rise due to heat generation of the electric coil 22 may destroy the coating of the electric coil 22 and cause smoke or fire.

  However, in the relay drive circuit 10 shown in FIG. 1, the switching element 11A and the switching element 12A are inserted in series in the path through which the coil current i21 flows. If one of them can be controlled to be turned off, the coil current i21 can be cut off to prevent smoke and fire due to continuous energization.

  In practice, there is normally no situation where both the switching element 11A and the switching element 12A fail simultaneously. Therefore, when the switching element 11A fails, the coil current i21 can be cut off by controlling the switching element 12A to be off. In addition, when the switching element 12A fails, the coil current i21 can be cut off by controlling the switching element 11A to be turned off.

  Similarly to the above, when the switching element 11B fails, the coil current i22 can be cut off by controlling the switching element 12B to turn off. In addition, when the switching element 12B fails, the coil current i22 can be cut off by controlling the switching element 11B to be turned off.

  Therefore, even if one of the switching element 11A and the switching element 12A fails, the length of the section T21B of the coil current i21 shown in FIG. 2 does not change. Further, even when one of the switching element 11B and the switching element 12B fails, the length of the section T22B of the coil current i22 shown in FIG. 2 does not change.

  Even if the switching element 13 fails, the coil current i21 can be cut off if the switching element 11A is switched off, and the coil current i22 can be cut off if the switching element 11B is switched off.

Second Embodiment
The second embodiment is a modification of the above-described first embodiment. The structure of the principal part of the vehicle-mounted electrical equipment including the relay drive circuit 10B of 2nd Embodiment is shown in FIG. FIG. 4 shows the diagnostic operation in the relay drive circuit 10B shown in FIG. In FIG. 3, the same elements as those in the first embodiment are denoted by the same reference numerals.

<Description of changes>
In the relay drive circuit 10 according to the first embodiment described above, even when any one of the switching elements 11A and 12A fails or when any one of the switching elements 11B and 12B fails, the coil current i21 And i22 can be reliably blocked. However, if a failure occurs in one component and that state is left unattended, a situation may occur in which the remaining components further fail. For example, there is a possibility that a state in which both the switching elements 11A and 12A have failed or a state in which both the switching elements 11B and 12B have failed occurs. That is, the coil current i21 or i22 may not be cut off, and smoke or fire may occur.

  In order to avoid a situation where a plurality of parts have failed as described above, it is necessary to repair the failure before a long time elapses after the first part failure occurs. In the second embodiment, the occurrence of a failure is detected by automatic diagnosis of the relay drive circuit 10B, and a function for notifying the failure when a failure is detected is added. Thereby, before falling into the worst situation, it is possible to prompt the vehicle user or the inspection operator to repair the failure.

<Description of added circuit>
In the relay drive circuit 10B shown in FIG. 3, the voltage VdA of the wiring 16A is applied to the analog input port 14d of the microcomputer 14 using the added wiring 18A. Further, the voltage VdB of the wiring 16B is applied to the analog input port 14e of the microcomputer 14 using the added wiring 18B.

  In addition, a function (program) for diagnosing a failure by monitoring the voltages VdA and VdB is added to the microcomputer 14. The operation is shown in FIG. Further, the display device 50 is connected to the microcomputer 14 in order to notify the result of diagnosis. The other configuration is the same as that of the relay drive circuit 10 of FIG.

<Description of voltages VdA and VdB>
The voltage VdA is a potential appearing on the wiring 16A between the two switching elements 11A and 12A connected in series. When no failure has occurred, the voltage VdA becomes an intermediate potential or a potential determined by the surrounding circuit at a timing when both of the two switching elements 11A and 12A are turned off. On the other hand, when a failure occurs in which the switching element 11A is kept on, the voltage VdA is always fixed at a value close to the ground potential. Further, when a failure occurs in which the switching element 12A is fixed while being on, the voltage VdA is always fixed to a value close to the potential of the power supply line 40. Therefore, the presence or absence of a failure can be identified by comparing the voltage VdA with a predetermined threshold value (for example, an intermediate potential).

  The voltage VdB is a potential appearing on the wiring 16B between the two switching elements 11B and 12B connected in series. When no failure has occurred, the voltage VdB becomes an intermediate potential or a potential determined by the surrounding circuit at the timing when both of the two switching elements 11B and 12B are turned off. On the other hand, when a failure occurs in which the switching element 11B remains fixed, the voltage VdB is always fixed to a value close to the ground potential. Further, when a failure occurs in which the switching element 12B is kept on, the voltage VdB is always fixed to a value close to the potential of the power supply line 40. Therefore, the presence or absence of a failure can be identified by comparing the voltage VdB with a predetermined threshold value (for example, an intermediate potential).

<Description of diagnostic operation>
When the microcomputer 14 in the relay drive circuit 10B shown in FIG. 3 performs the diagnostic operation shown in FIG. 4, a serious failure in the switching elements 11A, 11B, 12A, and 12B (a state fixed in the on state) is performed. It can automatically detect and notify the diagnosis result.

  When the power is turned on, the microcomputer 14 performs predetermined initialization in S11, and then identifies whether or not the diagnosis start condition is satisfied in S12. For example, it is assumed that the diagnosis is started every time a predetermined time elapses and the process proceeds to S13 and subsequent steps.

  In step S13, the microcomputer 14 identifies whether or not both of the control signals SGA and SGC are off. If this condition is satisfied, the process proceeds to S14, and if not, the process proceeds to S16.

  In step S14, the microcomputer 14 samples the voltage VdA applied to the analog input port 14d and measures this voltage value. In the next step S15, the presence or absence of a failure is identified by comparing the voltage value of VdA measured in S14 with a predetermined threshold value.

  When the control signals SGA and SGC are both off, the voltage VdA is usually an intermediate potential or a potential determined by the surrounding circuit as described above. However, when a failure occurs that is fixed when the switching element 11A is in the on state, VdA is at a low potential, and when a failure occurs when the switching element 12A is fixed at the on state, VdA is at a high potential. Therefore, the failure of the switching element 11A and the failure of the switching element 12A can be identified by comparing the voltage VdA in S15.

  In step S16, the microcomputer 14 identifies whether or not both of the control signals SGB and SGC are off, and if this condition is satisfied, the process proceeds to S17, and if not, the process proceeds to S19.

  In step S17, the microcomputer 14 samples the voltage VdB applied to the analog input port 14e and measures this voltage value. In the next step S18, the presence or absence of a failure is identified by comparing the VdB voltage value measured in S17 with a predetermined threshold value.

  When the control signals SGB and SGC are both off, the voltage VdB is usually an intermediate potential or a potential determined by the surrounding circuit as described above. However, when a failure occurs in which the switching element 11B is fixed in the on state, VdB is at a low potential, and when a failure occurs in which the switching element 12B is fixed in the on state, VdB is at a high potential. Therefore, the failure of the switching element 11B and the failure of the switching element 12B can be identified by comparing the voltage VdB in S18.

  In step S19, the microcomputer 14 identifies the presence / absence of failure detection by referring to the comparison result of S15 and S18. If a failure is detected, the microcomputer 14 proceeds to S20, and if not detected, returns to S12.

  In step S20, the microcomputer 14 notifies the user or the inspection operator of the detected failure state. For example, a message or symbol indicating that a failure has occurred in the relay drive circuit 10 is displayed on the screen of the display 50. In addition, information that can identify the location or part where the failure has occurred is automatically recorded in a nonvolatile memory (not shown) inside the microcomputer 14. In addition, the occurrence of a failure may be notified to an upper electronic control unit (ECU: not shown) by communication.

<Third Embodiment>
The second embodiment is a modification of the above-described first embodiment. The structure of the principal part of the vehicle-mounted electrical equipment including relay drive circuit 10C of 3rd Embodiment is shown in FIG. In FIG. 5, the same elements as those in the first embodiment are denoted by the same reference numerals.

<Description of changes>
In the relay drive circuit 10C of FIG. 5, switching elements 12C and 12D are employed instead of the switching elements 12A and 12B in FIG. Each of the switching elements 12C and 12D is a P-channel MOSFET (field effect transistor). Further, along with the switching elements 12C and 12D being changed to FETs, these peripheral circuits are also changed. However, similarly to the configuration of FIG. 1, the switching elements 11A and 12C are connected in series to the path of the coil current i21. The switching elements 11B and 12D are also connected in series with the path i22.

  As described above, among the two switching elements 11A and 12C connected in series, an N-channel type MOSFET is adopted on the low potential side and a P-channel type MOSFET is adopted on the high potential side, thereby ensuring these. It becomes possible to switch.

  A control signal output from the output port 14c of the microcomputer 14 is applied to the gate control terminal 12Cg of the switching element 12C. A control signal output from the output port 14f of the microcomputer 14 is applied to the gate control terminal 12Dg of the switching element 12D.

  Therefore, in the relay drive circuit 10C of FIG. 5, the microcomputer 14 controls on / off of the switching element 12C by a control signal output to the output port 14c, and turns on / off the switching element 12D by a control signal output to the output port 14f. Control. The other control is the same as that of the relay drive circuit 10 of FIG.

  In the relay drive circuit 10C shown in FIG. 5 as well, since the switching elements 11A and 12C are connected in series, even if one of the switching elements 11A and 12C fails, the remaining non-failed elements remain. The coil current i21 can be cut off reliably. In addition, since the switching elements 11B and 12D are connected in series, even if one of the switching elements 11B and 12D fails, the remaining elements that do not fail can reliably cut off the coil current i22. Therefore, it can be avoided that the coil current i21 or the coil current i22 continues to flow for a long time and an abnormal temperature rise occurs.

Here, the features of the above-described embodiment of the relay drive circuit according to the present invention are summarized and listed in the following [1] to [5], respectively.
[1] A relay (20) including an electric coil (21 or 22) having a restriction of continuous energization time;
A first switching element (11A or 11B) disposed in the energization path of the electric coil of the relay;
A second switching element (12A or 12B) disposed in the energization path in series with the first switching element;
When the electric coil is energized, both the first switching element and the second switching element are controlled to be on, and when the electric coil is de-energized, the first switching element and An energization control unit (microcomputer 14) that switches both of the second switching elements to an off state (see FIG. 2);
A relay drive circuit (10) comprising:
[2] The relay drive circuit according to [1] above,
Each of the first switching element and the second switching element is a semiconductor switch having a control input terminal, and has a different type of configuration.
A relay drive circuit characterized by that.
[3] The relay drive circuit according to [2] above,
The second switching element (12A or 12B) is connected to a higher potential side than the first switching element (11A or 11B);
Furthermore, a third switching element (13) for controlling the potential of the control input terminal (base terminal 12Ab) of the second switching element,
A relay drive circuit comprising:
[4] The relay drive circuit according to [3] above,
A plurality of the first switching elements and the second switching elements,
The output terminal of the third switching element is commonly connected to the control input terminals of the plurality of second switching elements (12A and 12B) (see FIG. 1).
A relay drive circuit characterized by that.
[5] The relay drive circuit according to any one of [1] to [4], further comprising:
At least when the electric coil is in a non-energized state, a fault monitoring unit (14, S12 to S18) that monitors the potential between the first switching element and the second switching element and identifies the presence or absence of a fault. ),
A relay drive circuit comprising:

10, 10B, 10C Relay drive circuit 11A, 11B Switching element 12A, 12B, 12C, 12D Switching element 13 Switching element 14 Microcomputer 14a, 14b, 14c, 14f Output port 14d, 14e Analog input port 15A, 15B Wiring 16A, 16B Wiring 17A, 17B Connection terminal 18A, 18B Wiring 20 Relay 21, 22 Electric coil 23, 24 Switch 30 DC electric motor 31, 32 Terminal 40 Power supply line 41 Ground line 45, 46 Connection terminal 50 Display 100 In-vehicle electrical equipment R11, R12 , R13, R14, R15, R16 Resistor R21, R22, R23, R24 Resistor D1, D2, D3 Diode i21, i22 Coil current i30 Motor current SGA, SGB, SG C Control signal VdA, VdB Monitored voltage

Claims (5)

A relay including an electrical coil having a continuous energization time constraint;
A first switching element disposed in an energization path of the electric coil of the relay;
A second switching element disposed in the energization path in series with the first switching element;
When the electric coil is energized, both the first switching element and the second switching element are controlled to be on, and when the electric coil is de-energized, the first switching element and An energization control unit that switches both of the second switching elements to an off state;
A relay drive circuit comprising: The relay drive circuit according to claim 1,
Each of the first switching element and the second switching element is a semiconductor switch having a control input terminal, and has a different type of configuration.
A relay drive circuit characterized by that. The relay drive circuit according to claim 2,
The second switching element is connected to a higher potential side than the first switching element;
A third switching element for controlling a potential of a control input terminal of the second switching element;
A relay drive circuit comprising: The relay drive circuit according to claim 3,
A plurality of the first switching elements and the second switching elements,
An output terminal of the third switching element is commonly connected to a plurality of control input terminals of the second switching element;
A relay drive circuit characterized by that. The relay drive circuit according to any one of claims 1 to 4, further comprising:
A fault monitoring unit for monitoring the potential between the first switching element and the second switching element and identifying the presence or absence of a fault when at least the electric coil is in a non-energized state;
A relay drive circuit comprising:

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