Patent Publication Number: US-2022239096-A1

Title: Load driving device

Description:
TECHNICAL FIELD 
     The present invention relates to a load driving device. 
     BACKGROUND ART 
     Conventionally known load driving devices as disclosed in Patent Document 1 include two semiconductor relays that are provided in a power supply path from a battery to a load and are connected in series to have parasitic diodes connected in opposite directions. One of the two semiconductor relays, which has the parasitic diode of which a forward direction extends from the battery to the load, serves as an anti-reverse connection semiconductor relay. This semiconductor relay suppresses excessive current at the time of connecting the battery in reverse to the load driving device, so as to protect circuit elements of the load driving device. 
     REFERENCE DOCUMENT LIST 
     Patent Document 
     
         
         Patent Document 1: JP 2007-082374 A 
       
    
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     Here, anti-reverse connection semiconductor relays, which receive a large load current, are generally made from an N-channel field effect transistor (FET) having low on-resistance value. If the N-channel FET is used as the anti-reverse connection semiconductor relay, it is necessary to connect a relay driver including a boosting power supply and a gate electrode of the anti-reverse connection semiconductor relay so as to drive the anti-reverse connection semiconductor relay. 
     However, when the battery is connected in reverse with opposite polarity to the load driving device, the relay driver may allow conduction between the ground and a gate electrode of the anti-reverse connection semiconductor relay depending on the relay driver&#39;s configuration. In this case, a potential difference may occur between a gate and a source of the anti-reverse connection semiconductor relay, to turn ON the anti-reverse connection semiconductor relay. This causes the risk of excessive current flowing through the load or the load driving device in an opposite direction to that at the time of load driving. 
     In view of the above problem, it is an object of the present invention to provide a load driving device that can reduce the risk of misoperation of an anti-reverse connection semiconductor relay when a battery is connected in reverse. 
     Means for Solving the Problem 
     To achieve the above object, a load driving device according to an aspect of the present invention includes: a drive circuit unit that drives a load; a plurality of power supply systems that individually supply power from a plurality of batteries to the drive circuit unit; a plurality of first semiconductor relays provided in the plurality of power supply systems, the first semiconductor relays each having a source electrode connected to a positive electrode of each of the plurality of batteries, having a drain electrode connected to the drive circuit unit, having a gate electrode that receives a drive signal output from a driver, and having a parasitic diode of which a forward direction extends from the positive electrode of each of the plurality of batteries to the drive circuit unit; and a first circuit unit that, when at least one battery of the plurality of batteries is connected in reverse with opposite polarity to the drive circuit unit, decreases a gate-source voltage of the first semiconductor relay of the power supply system to which the at least one battery is connected in reverse, down to a voltage that interrupts conduction between the source electrode and the drain electrode. 
     A load driving device according to another aspect of the present invention includes: a drive circuit unit that drives a load; one power supply system that supplies power from one battery to the drive circuit unit; a first semiconductor relay provided in the one power supply system, the first semiconductor relay having a source electrode connected to a positive electrode of the one battery, having a drain electrode connected to the drive circuit unit, having a gate electrode that receives a drive signal output from a driver, and having a parasitic diode of which a forward direction extends from the positive electrode of the one battery to the drive circuit unit; and a first circuit unit that, when the one battery is connected in reverse with opposite polarity to the drive circuit unit, decreases a gate-source voltage of the first semiconductor relay, down to a voltage that interrupts conduction between the source electrode and the drain electrode. 
     Effects of the Invention 
     According to the load driving device of the present invention, it is possible to reduce the risk of misoperation of the anti-reverse connection semiconductor relay at the time of connecting the battery in reverse. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram illustrating an example of a load driving device according to Embodiment 1. 
         FIG. 2  is a circuit diagram illustrating an example of a drive circuit unit of the load driving device and a load. 
         FIG. 3  is a circuit diagram illustrating an example of a circuit operation at the time of driving the load in  FIG. 1 . 
         FIG. 4  is a circuit diagram illustrating an example of a circuit operation at the time of connecting a battery in reverse in  FIG. 1 . 
         FIG. 5  is a circuit diagram illustrating an example of a load driving device according to Embodiment 2. 
         FIG. 6  is a circuit diagram illustrating an example of a circuit operation at the time of driving the load in  FIG. 5 . 
         FIG. 7  is a circuit diagram illustrating an example of a circuit operation at the time of connecting a battery in reverse in  FIG. 5 . 
         FIG. 8  is a circuit diagram illustrating an example of a circuit operation of a conventional load driving device at the time of connecting a battery in reverse. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Referring to the accompanying drawings, embodiments of the present invention will be described in detail below. 
     Embodiment 1 
       FIG. 1  illustrates an example of a load driving device according to Embodiment 1. A load driving device  100  includes a drive circuit unit  10  and a control circuit unit  20 . Drive circuit unit  10  controls an amount of current to be supplied from an in-vehicle battery  200  mounted in a vehicle to a load  300  that is also mounted in the vehicle. Control circuit unit  20  controls drive circuit unit  10 . A power supply system for supplying power from in-vehicle battery  200  to drive circuit unit  10  is configured for redundancy in view of improving the reliability of load driving device  100 . Specifically, the power supply system is configured for redundancy by a first power supply system and a second power supply system that supply power from a first battery  201  and a second battery  202 , respectively. 
     Control circuit unit  20  is, for example, a microcomputer and includes a central processing unit (CPU) or other processor, a random access memory (RAM) or other volatile memory, a read only memory (ROM) or other nonvolatile memory, and an input/output interface. Control circuit unit  20  receives power when an ignition switch (not illustrated) is turned ON. Control circuit unit  20  calculates a target value of current supply to load  300  based on, for example, a command signal from an upper control system (not illustrated) and output signals from various sensors (not illustrated). Then, control circuit unit  20  outputs a control signal to drive circuit unit  10  so as to bring the current supply amount from drive circuit unit  10  to load  300  closer to the target value. 
     Moreover, control circuit unit  20  determines whether a load current has fallen outside the target value so as to determine whether the first power supply system has an abnormality. If it is determined that the first power supply system is operating normally, control circuit unit  20  connects the first power supply system to a drive circuit while disconnecting the second power supply system from drive circuit unit  10 , as described below, so that the first power supply system supplies power to drive load  300 . In contrast, if an abnormality in the first power supply system is detected, control circuit unit  20  connects the second power supply system to the drive circuit while disconnecting the first power supply system from drive circuit unit  10 , as described below, so that the second power supply system supplies power to drive load  300 . That is, the second power supply system is used for backup when the first power supply system has an abnormality. 
     In load driving device  100 , the first power supply system includes a first positive terminal  101  and a first positive electrode line L 1 . First positive terminal  101  is connected to a positive electrode of first battery  201 . First positive electrode line L 1  connects first positive terminal  101  and a positive electrode side of drive circuit unit  10 . Moreover, in load driving device  100 , the second power supply system includes a second positive terminal  102  and a second positive electrode line L 2 . Second positive terminal  102  is connected to a positive electrode of second battery  202 . Second positive electrode line L 2  connects second positive terminal  102  and first positive electrode line L 1  at a connection node N 1 . Load driving device  100  further includes a negative terminal  103  and a negative electrode line L 3 . Negative terminal  103  is connected to negative electrodes of both of first and second batteries  201 ,  202  and is also grounded to the body, for example. Negative electrode line L 3  connects negative terminal  103  and a negative electrode side of drive circuit unit  10 . 
     Load driving device  100  includes a power supply relay unit  30  for switching connection and disconnection in relation to power supply from first and second batteries  201 ,  202  to drive circuit unit  10 . Power supply relay unit  30  includes a first power supply relay  31  provided in first positive electrode line L 1  and a second power supply relay  32  provided in second positive electrode line L 2 . First power supply relay  31  is a semiconductor relay that directly receives a control signal output from an output port P 1  of control circuit unit  20  or indirectly receives it through a driver, for example, and is then switched ON (conducted) or OFF (not conducted) according to the received control signal. Likewise, second power supply relay  32  is a semiconductor relay that directly receives a control signal output from an output port P 2  of control circuit unit  20  or indirectly receives it through a driver, for example, and is then switched ON or OFF according to the received control signal. First power supply relay  31  in an ON state allows conduction therethrough and power is supplied from first battery  201  to drive circuit unit  10 . Meanwhile, first power supply relay  31  in an OFF state does not allow conduction therethrough and the power supply from first battery  201  to drive circuit unit  10  is interrupted. The same applies to second power supply relay  32 . 
     In power supply relay unit  30 , first power supply relay  31  has an anti-parallel connected diode  31   d  of which a forward direction extends from drive circuit unit  10  to first positive terminal  101 . Likewise, second power supply relay  32  has an anti-parallel connected diode  32   d  of which a forward direction extends from drive circuit unit  10  to second positive terminal  102 . 
     Load driving device  100  further includes an anti-reverse connection relay unit  40  that suppresses excessive current to protect circuit elements of load driving device  100  when first and second in-vehicle batteries  201 ,  202  are connected in reverse with opposite polarity. Anti-reverse connection relay unit  40  includes a first anti-reverse connection relay  41  and a second anti-reverse connection relay  42 . First anti-reverse connection relay  41  is provided in first positive electrode line L 1  between first power supply relay  31  and drive circuit unit  10 . Second anti-reverse connection relay  42  is provided in second positive electrode line L 2  between second power supply relay  32  and connection node N 1 . First anti-reverse connection relay  41  and second anti-reverse connection relay  42  are both semiconductor relays that are switched ON or OFF according to a drive signal received from a single anti-reverse connection relay driver  50  as described below. First anti-reverse connection relay  41  receives a drive signal through a first signal line L 4 . Second anti-reverse connection relay  42  receives a drive signal through a second signal line L 5 . First anti-reverse connection relay  41  in an ON state allows conduction therethrough, whereas first anti-reverse connection relay  41  in an OFF state does not allow conduction therethrough. The same applies to second anti-reverse connection relay  42 . 
     First anti-reverse connection relay  41  has an anti-parallel connected diode  41   d  of which a forward direction extends from first positive terminal  101  to drive circuit unit  10 . Likewise, second anti-reverse connection relay  42  has an anti-parallel connected diode  42   d  of which a forward direction extends from second positive terminal  102  to drive circuit unit  10 . With the above forward direction of diode  41   d , when first anti-reverse connection relay  41  is turned OFF and first battery  201  is connected in reverse, a current path between first battery  201 , load  300 , and drive circuit unit  10  is blocked. Likewise, with the above forward direction of diode  42   d , when second anti-reverse connection relay  42  is turned OFF and second battery  202  is connected in reverse, a current path between second battery  202 , load  300 , and drive circuit unit  10  is blocked. 
     Power supply relay  31 ,  32  and anti-reverse connection relay  41 ,  42  are made from an N-channel metal oxide semiconductor field effect transistor (MOSFET) with low on-resistance value, in consideration of a load current (several A to several tens of A) flowing through load  300 . First power supply relay  31  has a drain electrode (D) connected to first positive terminal  101  and has a gate electrode (G) directly or indirectly connected to output port P 1  of control circuit unit  20 . First anti-reverse connection relay  41  has a drain electrode (D) connected to connection node N 1  and has a gate electrode (G) connected to anti-reverse connection relay driver  50  described below through first signal line L 4 . A resistor  104  is provided in first signal line L 4 . Source electrodes (S) of first power supply relay  31  and first anti-reverse connection relay  41  are connected to each other. Likewise, second power supply relay  32  has a drain electrode (D) connected to second positive terminal  102  and has a gate electrode (G) directly or indirectly connected to output port P 2  of control circuit unit  20 . Second anti-reverse connection relay  42  has a drain electrode (D) connected to connection node N 1  and has a gate electrode (G) connected to the anti-reverse connection relay driver described below through second signal line L 5 . A resistor  105  is provided in second signal line L 5 . Source electrodes (S) of second power supply relay  32  and second anti-reverse connection relay  42  are connected to each other. First and second power supply relays  31 ,  32 , and first and second anti-reverse connection relays  41 ,  42  have, as a parasitic diode, diodes  31   d ,  32   d ,  41   d , and  42   d , respectively. 
     Gate electrodes (G) of both of first and second anti-reverse connection relays  41 ,  42  are connected to anti-reverse connection relay driver  50  for driving first and second anti-reverse connection relays  41 ,  42 . This is because in order to turn ON first and second anti-reverse connection relays  41 ,  42  as the N-channel MOSFETs, their gate electrodes (G) have to receive higher voltage than a voltage (source voltage) of source electrodes (S) to which a power supply voltage is applied. Anti-reverse connection relay driver  50  includes a logic circuit  51 , a booster circuit  52 , and first and second driver relays  53 ,  54 . 
     When the first power supply system does not have an abnormality that hinders power supply from in-vehicle battery  200 , logic circuit  51  and booster circuit  52  receive power from first positive electrode line L 1  through a diode  106  having an anode connected to first positive electrode line L 1 . In contrast, when the first power supply system has an abnormality (for example, when a power supply voltage of first battery  201  decreases), logic circuit  51  and booster circuit  52  receive power from second positive electrode line L 2  through a diode  108  and an auxiliary power supply relay  107  that is turned ON. Auxiliary power supply relay  107  is a semiconductor relay that directly receives a control signal output from an output port P 3  of control circuit unit  20  or indirectly receives it through a driver, for example, and is then switched ON (conducted) or OFF (not conducted) according to the received control signal. Auxiliary power supply relay  107  in an ON state allows conduction therethrough, whereas auxiliary power supply relay  107  in an OFF state does not allow conduction therethrough. In the illustrated example, auxiliary power supply relay  107  is an N-channel MOSFET. Auxiliary power supply relay  107  has a drain electrode (D) connected to the drain electrode (D) of second power supply relay  32 , has a source electrode (S) connected to an anode of diode  108 , and has a gate electrode (G) connected to output port P 3  of control circuit unit  20 . A diode  107   d  as a parasitic diode of auxiliary power supply relay  107  has the forward direction extending from the source electrode (S) to the drain electrode (D). 
     First driver relay  53  and second driver relay  54  are connected in series between booster circuit  52  and negative electrode line L 3 . First driver relay  53  is switched ON or OFF according to a control signal output from logic circuit  51 . First driver relay  53  in an ON state allows conduction therethrough, whereas first driver relay  53  in an OFF state does not allow conduction therethrough. The same applies to second driver relay  54 . Anti-reverse connection relay driver  50  outputs a voltage of a connection node N 2  that connects first driver relays  53  and second driver relay  54 , as a drive signal of first and second anti-reverse connection relays  41 ,  42 . 
     In the illustrated example, first and second driver relays  53 ,  54  are N-channel MOSFETs. A source electrode (S) of first driver relay  53  and a drain electrode (D) of second driver relay  54  are connected to each other at connection node N 2 . A drain electrode (D) of first driver relay  53  receives a boosted voltage output from booster circuit  52 . A source electrode (S) of second driver relay  54  is connected to negative electrode line L 3 . Gate electrodes (G) of both of first driver relay  53  and second driver relay  54  are connected to logic circuit  51 . Connection node N 2  is connected to first signal line L 4  and second signal line L 5 . A diode  53   d  as a parasitic diode of first driver relay  53  and a diode  54   d  as a parasitic diode of second driver relay  54  each have a forward direction extending from the source electrode (S) to the drain electrode (D). 
     Logic circuit  51  having high internal impedance is configured to receive a control signal output from an output port P 4  of control circuit unit  20 . Logic circuit  51  outputs, according to the control signal output from output port P 4  of control circuit unit  20 , a control signal for turning ON either first driver relay  53  or second driver relay  54  to first driver relay  53  and second driver relay  54 . For example, logic circuit  51  outputs, according to a high-potential (H level) control signal output from output port P 4  of control circuit unit  20 , a control signal for turning ON first driver relay  53  and also turning OFF second driver relay  54 . Meanwhile, logic circuit  51  outputs, according to a low-potential (L level) control signal output from output port P 4  of control circuit unit  20 , a control signal for turning OFF first driver relay  53  and also turning ON second driver relay  54 . When first driver relay  53  is in an ON state, anti-reverse connection relay driver  50  outputs a drive signal at high potential equivalent to a boosted voltage output from booster circuit  52 . Meanwhile, when second driver relay  54  is in an ON state, anti-reverse connection relay driver  50  outputs a drive signal at low potential equivalent to the ground potential. 
     Load driving device  100  includes an operation shutdown circuit unit  60  that individually stops operations of first and second anti-reverse connection relays  41 ,  42 . Operation shutdown circuit unit  60  includes a first shutoff transistor  61  and a second shutoff transistor  62 , which stop operations of first anti-reverse connection relay  41  and second anti-reverse connection relay  42 , respectively. First shutoff transistor  61  connects first signal line L 4  and negative electrode line L 3 . Second shutoff transistor  62  connects second signal line L 5  and negative electrode line L 3 . First shutoff transistor  61  is switched ON or OFF according to a control signal output from an output port P 5  of control circuit unit  20 . First shutoff transistor  61  in an ON state allows conduction therethrough, whereas first shutoff transistor  61  in an OFF state does not allow conduction therethrough. Likewise, second shutoff transistor  62  is switched ON or OFF according to a control signal output from an output port P 6  of control circuit unit  20 . Second shutoff transistor  62  in an ON state allows conduction therethrough, whereas second shutoff transistor  62  in an OFF state does not allow conduction therethrough. 
     In the illustrated example, first and second shutoff transistors  61 ,  62  are NPN transistors. First shutoff transistor  61  has a collector electrode (C) connected to first signal line L 4  through a diode  63 , has an emitter electrode (E) connected to negative electrode line L 3 , and has a base electrode (B) connected to output port P 5  of control circuit unit  20  through a base resistor  64 . In addition, in first shutoff transistor  61 , a base-emitter resistor  65  is connected between the base electrode (B) and the emitter electrode (E). Likewise, second shutoff transistor  62  has a collector electrode (C) connected to second signal line L 5  through a diode  66 , has an emitter electrode (E) connected to negative electrode line L 3 , and has a base electrode (B) connected to output port P 6  of control circuit unit  20  through a base resistor  67 . In addition, in second shutoff transistor  62 , a base-emitter resistor  68  is connected between the base electrode (B) and the emitter electrode (E). When an emitter-collector voltage of first shutoff transistor  61  reaches a reverse withstand voltage thereof, diode  63  above functions to prevent backflow of a current from the emitter electrode (E) to the collector electrode (C). Moreover, when an emitter-collector voltage of second shutoff transistor  62  reaches a reverse withstand voltage thereof, diode  66  above functions to prevent backflow of a current from the emitter electrode (E) to the collector electrode (C). 
     Load driving device  100  includes a lockout circuit unit  70  for preventing misoperation of first and second anti-reverse connection relays  41 ,  42  at the time of connecting in-vehicle battery  200  in reverse. Lockout circuit unit  70  includes a first lockout transistor  71  (switch element) and a second lockout transistor  72  (switch element), which prevent misoperation of first anti-reverse connection relay  41  and second anti-reverse connection relay  42 , respectively. 
     First lockout transistor  71  is a semiconductor element that connects first signal line L 4  and first positive electrode line L 1  between first power supply relay  31  and first anti-reverse connection relay  41 . First lockout transistor  71  is switched ON or OFF according to a potential difference between first positive electrode line L 1  and negative electrode line L 3 . First lockout transistor  71  in an ON state allows conduction therethrough, whereas first lockout transistor  71  in an OFF state does not allow conduction therethrough. 
     Second lockout transistor  72  is a semiconductor element that connects second signal line L 5  and second positive electrode line L 2  between second power supply relay  32  and second anti-reverse connection relay  42 . Second lockout transistor  72  is switched ON or OFF according to a potential difference between second positive electrode line L 2  and negative electrode line L 3 . Second lockout transistor  72  in an ON state allows conduction therethrough, whereas second lockout transistor  72  in an OFF state does not allow conduction therethrough. 
     In the illustrated example, first and second lockout transistors  71 ,  72  are NPN transistors. First lockout transistor  71  has a collector electrode (C) connected to first signal line L 4  through a diode  73 , has an emitter electrode (E) connected to first positive electrode line L 1 , and has a base electrode (B) connected to negative electrode line L 3  through a base resistor  74 . In addition, in first lockout transistor  71 , a base-emitter resistor  75  is connected between the base electrode (B) and the emitter electrode (E). Likewise, second lockout transistor  72  has a collector electrode (C) connected to second signal line L 5  through a diode  76 , has an emitter electrode (E) connected to second positive electrode line L 2 , and has a base electrode (B) connected to negative electrode line L 3  through a base resistor  77 . In addition, in second lockout transistor  72 , a base-emitter resistor  78  is connected between the base electrode (B) and the emitter electrode (E). 
     When an emitter-collector voltage of first lockout transistor  71  reaches a reverse withstand voltage thereof, diode  73  above functions to prevent backflow of a current from the emitter electrode (E) to the collector electrode (C). Likewise, when an emitter-collector voltage of second lockout transistor  72  reaches a reverse withstand voltage thereof, diode  76  above functions to prevent backflow of a current from the emitter electrode (E) to the collector electrode (C). Now, the case of individually checking abnormalities of first power supply relay  31  and first anti-reverse connection relay  41  is considered, for example. In this case, power supply relay  31  is turned ON and also first driver relay  53  is turned OFF to turn ON second driver relay  54  so as to turn OFF first anti-reverse connection relay  41 . With this operation, it is assumed that first lockout transistor  71  has a collector voltage at the ground potential (for example, 0 V), has an emitter voltage equivalent to a power supply voltage (for example, +13 V), and has an emitter-collector voltage reaching a reverse withstand voltage thereof (for example, +5 V). However, diode  73  is provided between the collector electrode (C) of first lockout transistor  71  and first signal line L 4 , so that current flow from the emitter electrode (E) to the collector electrode (C) of first lockout transistor  71  is blocked. 
     Moreover, the following effects can be produced by connecting the emitter electrode (E) of first lockout transistor  71  to the downstream of first power supply relay  31 , and connecting the emitter electrode (E) of second lockout transistor  72  to the downstream of second power supply relay  32 . That is, if load  300  is not driven when first battery  201  is normally connected, first power supply relay  31  is turned OFF, so that dark current flowing through base-emitter resistor  75  and base resistor  74  can be suppressed. Likewise, if load  300  is not driven when second battery  202  is normally connected, second power supply relay  32  is turned OFF, so that dark current flowing through base-emitter resistor  78  and base resistor  77  can be suppressed. 
       FIG. 2  illustrates an example of load  300  and drive circuit unit  10 . For example, load  300  is a three-phase brushless motor with a U-phase coil  301 , a V-phase coil  302 , and a W-phase coil  303 . Drive circuit unit  10  is an inverter for driving the three-phase brushless motor. The three-phase brushless motor as load  300  includes a cylindrical stator (not illustrated) and a rotor  305 . In the stator, three-phase coils  301 ,  302 , and  303  are wound in the form of being connected in common to a neutral point  304 . Rotor  305  is a permanent magnet rotor provided rotatably at a central portion of the stator. 
     The inverter as drive circuit unit  10  is provided between first positive electrode line L 1  and negative electrode line L 3 . In drive circuit unit  10 , a U-phase arm, a V-phase arm, and a W-phase arm are connected in parallel between a positive electrode bus  10   a  connected to first positive electrode line L 1  and a negative electrode bus  10   b  connected to negative electrode line L 3 . The U-phase arm is configured by series-connecting an upper switching element  11  and a lower switching element  12 . The V-phase arm is configured by series-connecting an upper switching element  13  and a lower switching element  14 . The W-phase arm is configured by series-connecting an upper switching element  15  and a lower switching element  16 . U-phase coil  301  is connected between two switching elements  11 ,  12  of the U-phase arm. V-phase coil  302  is connected between two switching elements  13 ,  14  of the V-phase arm. W-phase coil  303  is connected between two switching elements  15 ,  16  of the W-phase arm. 
     In the inverter as drive circuit unit  10 , switching elements  11  to  16  include anti-parallel connected diodes  11   d  to  16   d , respectively, and control electrodes that can be externally controlled. Switching elements  11  to  16  perform switching operation between an ON state and an OFF state according to a control signal input to each control electrode. Switching elements  11  to  16  are arranged so that the forward directions of diodes  11   d  to  16   d  extend from negative electrode bus  10   b  to positive electrode bus  10   a . Switching elements  11  to  16  can be, for example, MOSFETs or insulated gate bipolar transistors (IGBTs). In the illustrated example, switching elements  11  to  16  are N-channel MOSFETs, and diodes  11   d  to  16   d  thereof are parasitic diodes. 
       FIG. 3  illustrates an example of a circuit operation of load driving device  100  at the time of supplying power from the first power supply system to drive the load. Control circuit unit  20  outputs the following control signals from output ports P 1  to P 6  at the time of supplying power from the first power supply system to drive the load. From output port P 1 , a control signal for turning ON first power supply relay  31  is output. From output port P 2 , a control signal for turning OFF second power supply relay  32  is output. From output port P 3 , a control signal for turning OFF auxiliary power supply relay  107  is output. From output port P 4 , a control signal for turning ON first driver relay  53  and also turning OFF second driver relay  54  is output. From output port P 5 , a control signal (for example, 0 V) for turning OFF first shutoff transistor  61  is output in order to maintain first anti-reverse connection relay  41  in an ON state. From output port P 6 , a control signal (for example, +5 V) for turning ON second shutoff transistor  62  is output in order to turn OFF second anti-reverse connection relay  42 . 
     Booster circuit  52  of anti-reverse connection relay driver  50  receives power supplied from first positive electrode line L 1  and outputs a boosted voltage (for example, +23 V) obtained by boosting a power supply voltage (for example, +13 V) of first battery  201 . In anti-reverse connection relay driver  50 , first driver relay  53  is in an ON state and second driver relay  54  is in an OFF state. Therefore, a drive signal output from anti-reverse connection relay driver  50  is equivalent to the boosted voltage (for example, +23 V) generated by booster circuit  52 . 
     At the time of driving the load with the first power supply system, first power supply relay  31  is turned ON according to the above control signal. Thus, a voltage of connection node N 3  in first positive electrode line L 1 , which is connected to the emitter electrode of first lockout transistor  71  and the source electrode of first anti-reverse connection relay  41 , is equivalent to the power supply voltage (for example, +13 V) of first battery  201 . In lockout circuit unit  70 , an emitter voltage of first lockout transistor  71  is equivalent to the power supply voltage (for example, +13 V) while a base voltage thereof is equivalent to a divided voltage (for example, +6.5 V) between base resistor  74  and base-emitter resistor  75 , so that first lockout transistor  71  is turned OFF. Moreover, in operation shutdown circuit unit  60 , a base voltage and an emitter voltage of first shutoff transistor  61  are both equivalent to the ground potential (for example, 0 V), so that first shutoff transistor  61  is turned OFF. Therefore, the drive signal, which is the boosted voltage (for example, +23 V) output from anti-reverse connection relay driver  50 , is applied to the gate electrode of first anti-reverse connection relay  41  with little voltage drop. As a result, the gate-source voltage of first anti-reverse connection relay  41 , which is a potential difference between the boosted voltage (for example, +23 V) and the power supply voltage (for example, +13 V), reaches or exceeds the gate threshold voltage (for example, +10 V), so that first anti-reverse connection relay  41  is turned ON. Since first power supply relay  31  and first anti-reverse connection relay  41  are both turned ON, a current can be supplied from the positive electrode of first battery  201  up to the negative electrode of first battery  201  via first positive electrode line L 1 , drive circuit unit  10 , and negative electrode line L 3  (see the thick solid line arrow of  FIG. 3 ). Thus, control circuit unit  20  outputs a control signal to drive circuit unit  10  so as to control an amount of current to be supplied from drive circuit unit  10  to load  300 , with which load  300  is driven. 
     Moreover, at the time of driving the load with the first power supply system, second power supply relay  32  is turned OFF according to the above control signal. Therefore, a voltage of connection node N 4  in second positive electrode line L 2 , which is connected to the emitter electrode of second lockout transistor  72  and the source electrode of second anti-reverse connection relay  42 , is equivalent to the ground potential (for example, 0 V). In lockout circuit unit  70 , since the emitter voltage of second lockout transistor  72  is equivalent to the ground potential (for example, 0 V) and the base voltage thereof is also equivalent to the ground potential (for example, 0 V), second lockout transistor  72  is turned OFF. However, in second shutoff transistor  62  of operation shutdown circuit unit  60 , the emitter voltage is equivalent to the ground potential (for example, 0 V) while the base voltage is equivalent to a divided voltage (for example, +2.5 V) between base resistor  67  and base-emitter resistor  68 . Thus, a base-emitter voltage of second shutoff transistor  62 , which is a potential difference between the base voltage (for example, +2.5 V) and the emitter voltage (for example, 0 V), reaches or exceeds a connection-portion saturation voltage (for example, +0.7 V), so that second shutoff transistor  62  is turned on. Therefore, a current flows from anti-reverse connection relay driver  50  to negative electrode line L 3  via second signal line L 5  and a collector and an emitter of second shutoff transistor  62  (see the hollow arrow of  FIG. 3 ). As a result, the drive signal being the boosted voltage (for example, +23 V) output from the anti-reverse connection relay driver  50  drops down to a forward voltage (for example, +0.7 V) of diode  66  by the current flowing through resistor  105 , and then is applied to the gate electrode of second anti-reverse connection relay  42 . In second anti-reverse connection relay  42 , a gate-source voltage (for example, +0.7 V) is lower than a gate threshold voltage (for example, +3 V), to turn OFF second anti-reverse connection relay  42 . Since second power supply relay  32  and second anti-reverse connection relay  42  are both turned OFF, current supply between the positive electrode of second battery  202  and drive circuit unit  10  is interrupted. 
     At the time of supplying power from the first power supply system to drive load  300 , control circuit unit  20  outputs the control signal as above, to electrically connect the first power supply system to drive circuit unit  10  as well as electrically disconnect the second power supply system from drive circuit unit  10 . 
     Note that control circuit unit  20  outputs the following control signals from output ports P 1  to P 6  at the time of supplying power from the second power supply system to drive load  300 . That is, from output port P 1 , a control signal for turning OFF first power supply relay  31  is output. From output port P 2 , a control signal for turning ON second power supply relay  32  is output. From output port P 3 , a control signal for turning ON auxiliary power supply relay  107  is output. From output port P 4 , a control signal for turning ON first driver relay  53  and also turning OFF second driver relay  54  is output. From output port P 5 , a control signal (for example, +5 V) for turning ON first shutoff transistor  61  is output in order to turn OFF first anti-reverse connection relay  41 . From output port P 6 , a control signal (for example, 0 V) for turning OFF second shutoff transistor  62  is output in order to turn ON second anti-reverse connection relay  42 . Also, in this way, substantially the same circuit operation as above is performed to electrically connect the second power supply system to drive circuit unit  10  as well as disconnect the first power supply system from drive circuit unit  10 . 
       FIG. 4  illustrates a circuit operation of load driving device  100  at the time of connecting first battery  201  in reverse to load driving device  100 . When first battery  201  is connected in reverse to load driving device  100 , a terminal voltage of negative terminal  103  is equivalent to the ground potential (for example, 0 V), whereas a terminal voltage of first positive terminal  101  is equivalent to a voltage (for example, −13 V) obtained by subtracting the power supply voltage (for example, +13 V) from the ground potential. In general, the first battery  201  is incorrectly connected in reverse to load driving device  100  when first battery  201  is replaced with an ignition switch (not illustrated) being turned OFF. At this time, no power is supplied to control circuit unit  20 , and thus no control signal is output from output ports P 1  to P 6  of control circuit unit  20 . As a result, all of first and second power supply relays  31 ,  32 , auxiliary power supply relay  107 , first and second driver relays  53 ,  54 , and first and second shutoff transistors  61 ,  62  are turned OFF. Moreover, if drive circuit unit  10  is an inverter for driving a brushless motor as load  300  as illustrated in  FIG. 2 , all of switching elements  11  to  16  are turned OFF as well. 
     However, at the time of connecting first battery  201  in reverse to load driving device  100 , a first closed circuit is formed, in which a current flows from first battery  201  even if no control signal is output from output ports P 1  to P 6  of control circuit unit  20 . In the first closed circuit, a current from the positive electrode of first battery  201  connected in reverse returns to the negative electrode of first battery  201  via base resistor  74 , base-emitter resistor  75 , and diode  31   d  of first power supply relay  31 . Since resistance values of base resistor  74  and base-emitter resistor  75  are high enough, a small amount of current flows through the first closed circuit. 
     When a current flows through the first closed circuit, a voltage of connection node N 3  drops at base resistor  74  and base-emitter resistor  75  and thus decreases from the ground potential (for example, 0 V). More specifically, the voltage of connection node N 3  is equivalent to a voltage (for example, −12.3 V) higher than the terminal voltage (for example, −13 V) of first positive terminal  101  because of the forward voltage (for example, +0.7 V) of diode  31   d  in first power supply relay  31 . The emitter voltage of first lockout transistor  71  in lockout circuit unit  70  is equivalent to a voltage (for example, −12.3 V) of connection node N 3 . Meanwhile, the base voltage of first lockout transistor  71  is equivalent to a voltage (for example, −6.2 V) obtained by dividing a potential difference between the ground potential and the voltage of connection node N 3  by base resistor  74  and base-emitter resistor  75 . Therefore, the base-emitter voltage (for example, +6.1 V) of first lockout transistor  71  reaches or exceeds the connection-portion saturation voltage (for example, +0.7 V), so that first lockout transistor  71  is turned ON and a base current flows through first lockout transistor  71  (see the hollow arrow of  FIG. 4 ). As a result, a second closed circuit is formed, in which a current from the positive electrode of first battery  201  connected in reverse flows in load driving device  100  from negative terminal  103  to first positive terminal  101  and returns to the negative electrode of first battery  201  (see the thick solid line arrow of  FIG. 4 ). In the second closed circuit, the current flows in load driving device  100  in the order of diode  54   d  of second driver relay  54 , resistor  104 , diode  73 , the collector and the emitter of first lockout transistor  71 , and diode  31   d  of first power supply relay  31 . Note that a resistance value of resistor  104  is high enough, and thus, a small amount of current flows through the second closed circuit. 
     When the current flows in the second closed circuit, the gate voltage of first anti-reverse connection relay  41  drops at resistor  104  and thus decreases from the ground potential (for example, 0 V). More specifically, the gate voltage of first anti-reverse connection relay  41  is equivalent to a voltage (−11.6 V) higher than the voltage (for example, −12.3 V) of connection node N 3  because of the forward voltage (for example, +0.7 V) of diode  73 . In first anti-reverse connection relay  41 , a gate-source voltage (for example, +0.7 V) that is a potential difference between the gate voltage (for example, −11.6 V) and the source voltage (for example, −12.3 V) is lower than the gate threshold voltage (for example, 3 V), so that first anti-reverse connection relay  41  is turned OFF. As a result, the current path is blocked, which has been formed in an opposite direction to that at the time of load driving, that is, in a direction from the positive electrode of first battery  201  connected in reverse back to the negative electrode of first battery  201  via drive circuit unit  10  (see the thick broken line arrow of  FIG. 4 ). 
     When first battery  201  is connected in reverse to load driving device  100 , second anti-reverse connection relay  42  is also turned OFF as follows. In second power supply relay  32  in an OFF state, the drain voltage is equivalent to the power supply voltage (for example, +13 V) of second battery  202 , and the source voltage is equivalent to the ground potential (for example, 0 V), so that a current flowing from the source electrode to the drain electrode via diode  32   d  is interrupted. As a result, a current flowing through base resistor  77  and base-emitter resistor  78  of lockout circuit unit  70  is interrupted as well, so that the voltage of connection node N 4  is equivalent to the ground potential (for example, 0 V). Moreover, in second lockout transistor  72  of lockout circuit unit  70 , the base voltage and the emitter voltage are both equivalent to the ground potential (for example, 0 V), so that second lockout transistor  72  is turned OFF. As a result, the gate voltage of second anti-reverse connection relay  42  is equivalent to a voltage (for example, −0.7 V) lower than the ground potential (for example, 0 V) because of the forward voltage (for example, +0.7 V) of diode  54   d  of second driver relay  54 . However, in second anti-reverse connection relay  42 , the source voltage is equal to the voltage of connection node N 4  at the ground potential (for example, 0 V) compared with the gate voltage (for example, −0.7 V), that is, the source voltage is higher than the gate voltage, so that second anti-reverse connection relay  42  is turned OFF. 
     In first shutoff transistor  61 , the collector voltage is equivalent to the gate voltage (for example, −11.6 V) of first anti-reverse connection relay  41  and the emitter voltage is equivalent to the ground potential (for example, 0 V). At this time, the emitter-collector voltage (for example, 11.6 V) of first shutoff transistor  61  exceeds the reverse withstand voltage thereof (for example, 5 V). However, since diode  63  is connected in series to the collector electrode of first shutoff transistor  61 , a current from the emitter electrode to the collector electrode of first shutoff transistor  61  is blocked. 
     Note that the circuit operation of load driving device  100  at the time of connecting second battery  202  in reverse is substantially the same as the circuit operation of load driving device  100  at the time of connecting first battery  201  in reverse, and thus, description thereof is omitted. Referring next to  FIG. 8  illustrating a conventional load driving device  100   cvt , effects of load driving device  100  are described below. 
       FIG. 8  illustrates a circuit operation of conventional load driving device  100   cvt  at the time of connecting first battery  201  in reverse to conventional load driving device  100   cvt . Conventional load driving device  100   cvt  differs from load driving device  100  in that anti-reverse connection relay drivers  50   a ,  50   b  are provided for first and second anti-reverse connection relays  41 ,  42  in one-to-one correspondence and operation shutdown circuit unit  60  and lockout circuit unit  70  are not provided. Note that the same components as load driving device  100  are denoted by the same reference symbols and thus are described briefly or are not described. 
     Anti-reverse connection relay driver  50   a  for first anti-reverse connection relay  41  receives a control signal output from output port P 4  of control circuit unit  20  so as to control first and second driver relays  53 ,  54 . Likewise, anti-reverse connection relay driver  50   b  for second anti-reverse connection relay  42  receives a control signal output from an output port P 4 ′ of control circuit unit  20  so as to control first and second driver relays  53 ,  54 . 
     When first battery  201  is connected in reverse to load driving device  100   cvt , no control signal is output from output ports P 1  to P 4 ′, so that all of first and second power supply relays  31 ,  32 , auxiliary power supply relay  107 , and first and second driver relays  53 ,  54  are turned OFF. The gate voltage of first anti-reverse connection relay  41  is equivalent to a voltage (for example, −0.7 V) lower than the ground potential (for example, 0 V) because of the forward voltage (for example, +0.7 V) of diode  54   d  of second driver relay  54 . The source voltage of first anti-reverse connection relay  41  is equivalent to a voltage (for example, −12.3 V) higher than the voltage (for example, −13 V) of the negative electrode of first battery  201  connected in reverse because of the forward voltage of diode  31   d  of first power supply relay  31 . As a result, in first anti-reverse connection relay  41 , the gate-source voltage (for example, +11.6 V) reaches or exceeds the gate threshold voltage (for example, +3 V), so that first anti-reverse connection relay  41  is turned ON. 
     When first anti-reverse connection relay  41  is turned ON, a current from the positive electrode of first battery  201  connected in reverse flows in reverse in the order of drive circuit unit  10 , the drain and the source of first anti-reverse connection relay  41 , and diode  31   d  of first power supply relay  31  and then returns to the negative electrode (see the thick solid line arrow of  FIG. 8 ). For example, as illustrated in  FIG. 2 , if drive circuit unit  10  is an inverter for driving the brushless motor as load  300 , in drive circuit unit  10 , a current flows in reverse from negative electrode line L 3  to first positive electrode line L 1  via diodes  11   d  to  16   d . Such backflow current does not flow through a resistor having a sufficiently large resistance value, and thus turns into excessive current. This means the risk of reducing the durability of load  300  or the circuit element of load driving device  100   cvt , or causing element breakdown. 
     However, load driving device  100  includes lockout circuit unit  70  as described above, so that when first battery  201  is connected in reverse to load driving device  100 , first anti-reverse connection relay  41  can be autonomously turned OFF. Therefore, the current path extending in an opposite direction to that at the time of load driving, that is, in a direction from the positive electrode of first battery  201  connected in reverse back to the negative electrode via drive circuit unit  10 , is blocked. It is accordingly possible to suppress reduction in durability of load  300  or the circuit element of load driving device  100  caused by the excessive current. 
     Moreover, load driving device  100  includes operation shutdown circuit unit  60  as described above, so that operations of first and second anti-reverse connection relays  41 ,  42  can be individually stopped. Therefore, the two anti-reverse connection relays for first and second anti-reverse connection relays  41 ,  42  can be replaced with one anti-reverse connection relay driver  50 , by which enlargement and cost increase of load driving device  100  can be suppressed. 
     Embodiment 2 
       FIG. 5  illustrates an example of a load driving device according to Embodiment 2. Note that the same components as Embodiment 1 are denoted by the same reference symbols and thus are described briefly or are not described. 
     A load driving device  100   a  differs from load driving device  100  in that a power supply system for supplying power from battery  200  to drive circuit unit  10  is not configured for redundancy. Specifically, load driving device  100   a  includes only the first power supply system for supplying power from first battery  201 , and it does not include the second power supply system of load driving device  100 , which supplies power from second battery  202 . Therefore, load driving device  100   a  dispenses with second positive electrode line L 2 , second signal line L 5 , second positive terminal  102 , second power supply relay  32 , second anti-reverse connection relay  42 , resistor  105 , auxiliary power supply relay  107 , and diode  108  of load driving device  100 . Moreover, load driving device  100   a  does not include second anti-reverse connection relay  42  and thus dispenses with operation shutdown circuit unit  60  for individually stopping the operations of first and second anti-reverse connection relays  41 ,  42  of load driving device  100 . Furthermore, a lockout circuit unit  70   a  of load driving device  100   a  dispenses with the circuit element of load driving device  100 , which prevents misoperation of second anti-reverse connection relay  42 . Specifically, second lockout transistor  72  and corresponding circuit elements, that is, diode  76 , base resistor  77 , and base-emitter resistor  78  of load driving device  100  are omitted. 
       FIG. 6  illustrates an example of a circuit operation of load driving device  100   a  at the time of driving load  300 . Control circuit unit  20  outputs the following control signals from output port P 1 , P 4  at the time of driving load  300 . From output port P 1 , a control signal for turning ON first power supply relay  31  is output. From output port P 4 , a control signal for turning ON first driver relay  53  and also turning OFF second driver relay  54  is output. In this state, substantially the same circuit operation as in load driving device  100  of  FIG. 3  is performed to turn OFF first lockout transistor  71  of lockout circuit unit  70   a , so that first anti-reverse connection relay  41  is turned ON. Since both of first power supply relay  31  and first anti-reverse connection relay  41  are turned ON, a current can be supplied from the positive electrode of first battery  201  up to the negative electrode of first battery  201  via first positive electrode line L 1 , drive circuit unit  10 , and negative electrode line L 3  (see the thick solid line arrow of  FIG. 6 ). As a result, when control circuit unit  20  outputs a control signal to drive circuit unit  10 , an amount of current to be supplied from drive circuit unit  10  to load  300  is controlled to drive load  300 . 
       FIG. 7  illustrates a circuit operation of load driving device  100   a  at the time of connecting first battery  201  in reverse to load driving device  100   a . In the case of connecting first battery  201  in reverse to load driving device  100   a , no power is supplied to control circuit unit  20  as described above, so that no control signal is output from output port P 1 , P 4  of control circuit unit  20 . Therefore, all of first power supply relay  31 , and first and second driver relays  53 ,  54  are turned OFF. Moreover, if drive circuit unit  10  is an inverter for driving the brushless motor as load  300  as illustrated in  FIG. 2 , all of switching elements  11  to  16  are turned OFF as well. Even in this state, substantially the same circuit operation as load driving device  100  of  FIG. 4  is performed, to form the above-described first closed circuit, so that the base-emitter voltage of first lockout transistor  71  reaches or exceeds the connection-portion saturation voltage and then first lockout transistor  71  is turned ON. As a result, the base current flows through first lockout transistor  71  (see the hollow arrow of  FIG. 7 ). Then, substantially the same circuit operation as load driving device  100  of  FIG. 4  is performed, to form the above-described second closed circuit (see the thick solid line arrow of  FIG. 7 ), so that the gate-source voltage of first anti-reverse connection relay  41  is lower than the gate threshold voltage and then first anti-reverse connection relay  41  is turned OFF. As a result, the current path extending in an opposite direction to that at the time of load driving, that is, in a direction from the positive electrode of first battery  201  connected in reverse back to the negative electrode via drive circuit unit  10 , is blocked (see the thick broken line arrow of FIG.  7 ). 
     Since even non-redundant load driving device  100   a  having the single power supply system as above includes lockout circuit unit  70   a , when first battery  201  is connected in reverse to load driving device  100   a , first anti-reverse connection relay  41  can be autonomously turned OFF. Therefore, the current path extending in an opposite direction to that at the time of load driving, that is, in a direction from the positive electrode of first battery  201  connected in reverse back to the negative electrode via drive circuit unit  10  is blocked. It is accordingly possible to suppress reduction in durability of load  300  and the circuit element of load driving device  100  caused by excessive current. 
     Note that load driving device  100  has the configuration that one anti-reverse connection relay driver  50  is provided for first and second anti-reverse connection relays  41 ,  42 , and operation shutdown circuit unit  60  individually stops operations of first and second anti-reverse connection relays  41 ,  42 . However, load driving device  100  may have such configuration that operation shutdown circuit unit  60  is omitted, and anti-reverse connection relay drivers  50   a ,  50   b  are provided for first and second anti-reverse connection relays  41 ,  42  in one-to-one correspondence as in conventional load driving device  100   cvt.    
     The circuit configuration of operation shutdown circuit unit  60  and lockout circuit unit  70 ,  70   a  is merely given by way of example. For example, first and second shutoff transistors  61 ,  62  and first and second lockout transistors  71 ,  72  may be MOSFETs or other switching elements in place of the NPN transistors. In short, operation shutdown circuit unit  60  has only to individually decrease the gate voltages of first and second anti-reverse connection relays  41 ,  42  according to a control signal output from control circuit unit  20 . That is, operation shutdown circuit unit  60  has only to individually decrease the gate-source voltage of first anti-reverse connection relay  41  and the gate-source voltage of second anti-reverse connection relay  42  so as to selectively maintain first and second anti-reverse connection relays  41 ,  42  in an OFF state. Moreover, lockout circuit unit  70 ,  70   a  has only to autonomously establish conduction between the gate electrode and the source electrode of first anti-reverse connection relay  41  according to a potential difference between the source voltage of first anti-reverse connection relay  41  and the ground potential at the time of connecting first battery  201  in reverse. In addition, lockout circuit unit  70  has only to autonomously establish conduction between the gate electrode and the source electrode of second anti-reverse connection relay  42  according to the potential difference between the source voltage of second anti-reverse connection relay  42  and the ground potential at the time of connecting second battery  202  in reverse. 
     Load driving device  100 ,  100   a  is configured assuming that at the time of connecting first and second batteries  201 ,  202  in reverse, the gate electrodes of both of first and second anti-reverse connection relays  41 ,  42  are conducted to negative electrode line L 3  via anti-reverse connection relay driver  50 . Therefore, anti-reverse connection relay driver  50  may have another circuit configuration as long as the gate electrodes of both of first and second anti-reverse connection relays  41 ,  42  can be conducted to negative electrode line L 3  via anti-reverse connection relay driver  50  at the time of connecting the battery in reverse. For example, in anti-reverse connection relay driver  50 , first and second driver relays  53 ,  54  may be P-channel MOSFETs in place of the N-channel MOSFETs. 
     Drive circuit unit  10  is described above as the inverter for driving load  300  as the brushless motor by way of example, but the brushless motor may be used as an actuator of an electric power steering system or an electric braking system. Moreover, drive circuit unit  10  may drive a solenoid used in an internal engine injector and an automotive transmission or other inductive load in place of the brushless motor. 
     Load driving device  100  is configured for redundancy by the two power supply systems: the first power supply system for supplying power from first battery  201  and the second power supply system for supplying power from second battery  202 . However, load driving device  100  may be configured for redundancy by three or more power supply systems in place of the above two systems. In this case, a shutoff transistor and a lockout transistor may be provided for each of the third and subsequent power supply systems in addition to shutoff transistor  61 ,  62  and lockout transistor  71 ,  72  provided in each of the two power supply systems. 
     REFERENCE SYMBOL LIST 
     
         
           10  Drive circuit unit 
           30  Power supply relay unit 
           31  First power supply relay 
           32  Second power supply relay 
           40  Anti-reverse connection relay unit 
           41  First anti-reverse connection relay 
           41   d  Diode 
           42  Second anti-reverse connection relay 
           42   d  Diode 
           50  Anti-reverse connection relay driver 
           60  Operation shutdown circuit unit 
           61  First operation shutoff transistor 
           62  Second operation shutoff transistor 
           70 ,  70   a  Lockout circuit unit 
           71  First lockout transistor 
           72  Second lockout transistor 
           73 ,  76  Diode 
           100 ,  100   a  Load driving device 
           200  Battery 
           201  First battery 
           202  Second battery 
           300  Load 
         L 1  First positive electrode line 
         L 2  Second positive electrode line 
         L 3  Negative electrode line 
         L 4  First signal line 
         L 5  Second signal line