Power reverse connection protection circuit

Abstract

To provide a power supply reverse connection protection circuit capable of preventing semiconductor elements for reverse connection protection from being in a breakdown state even when a negative polarity surge voltage is applied to a power supply side.SOLUTION: A power supply reverse connection protection circuit 11 is connected between an inverter circuit 2 that drives a motor 1, and the battery 9 that supplies a drive power supply VBATT to the inverter circuit 2. A reverse connection prevention relay 10 is connected between a connection terminal of the battery 9 and a power supply point of the inverter circuit 2. A power supply unit 15 for driving elements supplies a power supply VRG generated by the battery 9 to a gate of the reverse connection prevention relay 10 via a diode 14. A reverse connection protection unit 21 has a transistor 18 connected between an anode of the diode 14 and a connection terminal to which a positive electrode of the battery 9 is connected, and when the battery 9 is connected with reverse polarity, turns on the transistor 18 to form a current path from the ground to the connection terminal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a configuration that avoids damage to circuit elements constituting a device when a DC power supply is connected to the device with an incorrect polarity (reverse connection) during power supply connection. [Background technology]

[0002] For example, Patent Document 1 discloses a power supply reverse connection protection device for a power supply control device that controls the supply of power to a load using a semiconductor element for power supply control from a DC power supply. This device prevents damage to the semiconductor element for power supply control when the power supply polarity is incorrectly reversed when connecting the DC power supply. In this configuration, an avalanche breakdown state is avoided when the voltage on the load side rises by adding a gate resistor to the reverse connection protection semiconductor element. In the following, "reverse connection" or "reverse polarity" simply refers to connecting a DC power supply to a drive circuit or the like with the positive and negative polarities of the power supply reversed from their original state. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2013-38908 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, in the configuration of Patent Document 1, since a P-channel MOSFET is used as the protective semiconductor element, if a negative surge voltage is applied and the power supply side becomes negative, it is conceivable that the source voltage will fall below the threshold voltage and the FET will turn off. In that case, a large voltage will be applied between the source and drain of the FET, which is conceivable to lead to avalanche breakdown.

[0005] The present invention has been made in view of the above circumstances, and its purpose is to provide a power supply reverse connection protection circuit that can prevent a semiconductor element for reverse connection protection from breaking down even when a negative polarity surge voltage is applied to the power supply side. [Means for solving the problem]

[0006] According to the power supply reverse connection protection circuit of claim 1, the circuit is connected between a drive circuit that drives a load and a DC power supply that supplies power to the drive circuit. The first protective switching element is connected between the connection terminal of the DC power supply and the power supply point of the drive circuit, and the element drive power supply unit supplies the element drive power generated from the DC power supply to the drive terminal of the first protective switching element via a forward first diode.

[0007] The reverse polarity protection section has a second protective switching element connected between the anode of the first diode and the connection terminal. When a DC power supply is connected in reverse polarity, the second protective switching element is turned on, forming a current path from ground to the connection terminal. A DC power supply may be connected in reverse polarity when it is disconnected and then reconnected; therefore, no voltage is applied to the drive terminal of the first protective switching element. Since a first resistive element is connected between the connection terminal and the drive terminal, both terminals are at the same potential, and the first protective switching element is turned off. Consequently, the drive circuit is isolated from the DC power supply and protected.

[0008] On the other hand, if the DC power supply is properly connected, the drive terminals of the first protective switching element are supplied with power by the element drive power supply unit, so the first protective switching element is turned on. From this state, if a negative surge voltage is applied to the positive terminal side of the DC power supply, the drive terminals of the first protective switching element will no longer be supplied with power, but the charge that is charged at that time will turn on the first protective switching element. Then, as the potential of the connection terminal drops significantly to the negative side, the charged charge is discharged through the first resistive element and remains on until it falls below the threshold voltage. This prevents a high voltage from being applied between the conductive terminals of the first protective switching element, that is, between the connection terminals of the DC power supply and the power supply point of the drive circuit, and thus protects the first protective switching element.

[0009] According to the power supply reverse connection protection circuit described in claim 2, since a capacitor is connected between the connection terminal and the drive terminal, the charge stored in the capacitor can maintain the ON state of the first protective switching element for a longer period of time.

[0010] According to the power supply reverse connection protection circuit described in claim 3, a Zener diode is connected between the connection terminal and the drive terminal. When a negative surge voltage is applied and the potential of the connection terminal drops significantly, the Zener diode operates, resulting in a Zener voltage between the connection terminal and the drive terminal. This allows for more reliable protection of the first protective switching element. [Brief explanation of the drawing]

[0011] [Figure 1] This is one embodiment, and the diagram shows a power supply reverse connection protection circuit. [Figure 2] Functional block diagram (Part 1) showing the configuration of the power steering system. [Figure 3] Functional block diagram (part 2) showing the configuration of the power steering system. [Figure 4] A diagram showing the current flow when the battery is connected with reverse polarity. [Figure 5] Figure showing the waveforms of each voltage when (1) starting from the normal state, (2) applying a negative surge voltage, and (3) returning to the normal state again [Figure 6] Figure showing the voltages of each part [Figure 7] Figure showing an enlarged view of the periods (1) and (2) shown in Fig. 5

Mode for Carrying Out the Invention

[0012] Hereinafter, an embodiment will be described. As shown in Fig. 1, the motor 1 as a load is, for example, mounted on a vehicle and is, for example, an actuator of an electric power steering system. The motor 1 is driven by an inverter circuit 2 which is an example of a drive circuit. The inverter circuit 2 is constituted by connecting six switching elements 3 such as N-channel MOSFETs in a three-phase bridge connection. A shunt resistor 4 for current detection is connected between each phase lower arm of the inverter circuit 2 and the ground.

[0013] The output terminals of each phase of the inverter circuit 2 are connected to the other ends of the phase windings 6 of the star connection of the motor 1 via a motor relay 5. The switching element constituting the motor relay 5 is also, for example, an N-channel MOSFET. A capacitor 8 is connected between the power supply point 7 of the inverter circuit 2 and the ground. Power from the battery 9 mounted on the vehicle is supplied to the power supply point 7 via a reverse connection preventing relay 10 corresponding to a first protection switching element. The reverse connection preventing relay 10 is also a switching element such as an N-channel MOSFET, etc., whose drain is connected to the power supply point 7 and whose source is connected to the positive electrode of the battery 9. The withstand voltage of the reverse connection preventing relay 10 is generally about 50V to 70V.

[0014] The reverse connection prevention relay 10 is part of the power supply reverse connection protection circuit 11. The power supply VRG is generated from the power supply of the battery 9 via a boost circuit (not shown). The voltage of the power supply VRG is set to approximately 26V, for example, if the voltage of the battery 9 is 12V. The power supply VRG is supplied to the gate of the reverse connection prevention relay 10 via a series circuit of a P-channel MOSFET 12, a resistor 13, and a first diode 14. The FET 12, resistor 13, and first diode 14 constitute the element drive power supply unit 15.

[0015] A series circuit of a second resistor 16, a second diode 17, and an NPN transistor 18 is connected between the anode of the first diode 14 and ground. The NPN transistor 18 corresponds to a second protective switching element. The anode of the second diode 17 is connected to the anode of the first diode 14. A series circuit of a third diode 19 and a third resistor 20 is connected between ground and the base of the transistor 18. These components 16 to 20 constitute a reverse connection protection unit 21.

[0016] A bidirectional Zener diode 22, a first resistor 23, and a capacitor 24 are connected in parallel between the emitter of transistor 18 and the gate of reverse-connection protection relay 10. This constitutes the power supply reverse-connection protection circuit 11. The emitter of transistor 18 and the source of reverse-connection protection relay 10 correspond to the connection terminals to which the positive terminal of battery 9 is connected.

[0017] As shown in Figure 2, the electric power steering system 100 provides steering assist torque to the steering shaft 92 to assist the steering torque provided by the driver. A torque sensor 94 for detecting steering torque is located on the steering shaft 92, which is connected to the steering wheel 91. A pinion gear 96 is provided at the end of the steering shaft 92, and the pinion gear 96 meshes with the rack shaft 97. A pair of wheels 98 are rotatably connected to both ends of the rack shaft 97 via tie rods or the like. The rotational motion of the steering shaft 92 is converted into linear motion of the rack shaft 97 by the pinion gear 96, and the pair of wheels 98 are steered by an angle corresponding to the linear displacement of the rack shaft 97.

[0018] The electric power steering system 100 consists of a steering assist motor 1 that generates steering assist torque, a reduction gear 89 that reduces the rotational output of the motor 1 and transmits it to the steering shaft 92, and a motor drive unit 40 that drives the motor 1. The motor drive unit 40 is connected to a battery 9 which serves as a "DC power source". In this embodiment, the motor 1 is a three-phase AC brushless motor. The inverter circuit 2 and the power supply reverse connection protection circuit 11 in this embodiment are built into the motor drive unit 40.

[0019] The electric power steering system 100 shown in Figure 2 is a pinion-assist type, but it may also be a rack-assist type, as shown in Figure 3, the electric power steering system 101. In the rack-assist type, the reduction gear 89 is interposed on the rack shaft 97 side, rather than on the steering shaft 92 and pinion gear 96 side.

[0020] Next, the operation of this embodiment will be described. <Operation when battery is properly connected> When the ignition switch (not shown) is turned on, the power supply VRG is generated by the power supplied from the battery 9, and other ECUs (Electronic Control Units) and other components (not shown) operate normally. Then, the FET 12 is turned on by the ECU, and the gate of the reverse-connection prevention relay 10 is charged by the power supply VRG via the resistor 13 and diode 14. The reverse-connection prevention relay 10 turns on, and power from the battery 9 is supplied to the inverter circuit 2 via the channel of the reverse-connection prevention relay 10. The above operation corresponds to part (1) shown in Figure 5.

[0021] <Operation when battery is connected in reverse> The reverse connection of battery 9 is expected to occur, for example, when the vehicle is stopped and the user temporarily removes and then reconnects battery 9. In other words, before the reverse connection occurs, the gate of the reverse connection prevention relay 10 is not charged. When battery 9 is reverse-connected from this state, the emitter of transistor 18 becomes -12V.

[0022] As shown in Figure 4, current flows from ground through diode 19 and resistor 20 to the emitter of transistor 18, turning transistor 18 on. This causes current to flow from ground through resistor 16, diode 17 and transistor 18 to the negative terminal of battery 9, but no current flows to the gate of reverse-connection protection relay 10 due to diode 14, so the gate is not charged. At this time, the source and gate of reverse-connection protection relay 10 are at the same potential due to resistor 23, so reverse-connection protection relay 10 turns off. Therefore, the inverter circuit 2 is disconnected from battery 9.

[0023] Here, in order to turn off the reverse connection prevention relay 10 when the battery is reverse connected, the gate-source voltage V of the reverse connection prevention relay 10 at that time GS The voltage must be less than the threshold voltage Vth1. Let Vsat be the collector-emitter saturation voltage of transistor 18, Vth2 be the threshold voltage, and let Vf1 and Vf2 be the forward voltages of diodes 17 and 14, respectively. Then, Vf1 + Vsat = Vf2 + V GS …(1) Therefore, the voltage V between the gate and the source GS is V GS = Vsat + Vf1 - Vf2 < Vth1 …(2) needs to satisfy this condition.

[0024] <Operation when a negative - polarity surge voltage is applied> When a negative - polarity surge voltage is applied to the positive electrode of battery 2 from the state of normal connection of the battery shown in (1) in Fig. 5, both the voltage V BATT and the voltage IG of battery 2 supplied through the ignition switch fall below 0V. As a result, the power supply to the ECU is not provided, the power supply VRG cannot be generated, and the anode potential of diode 14 also decreases. Hereinafter, the application of the negative - polarity surge voltage may be referred to as "negative surge application".

[0025] Let the voltage between the base and the emitter of transistor 18 in the reverse - connection protection unit 21 be V BE , the saturation voltage between the collector and the emitter be Vsat, the threshold voltage be Vth2, and the forward voltage of diode 17 be Vf1. At this time (V BE > Vth2) holds, and the anode voltage VDi is VDi = V BATT + Vsat + Vf1 …(3) The voltage V between the gate and the source of the reverse - connection prevention relay 10 GS does not become the anode voltage VDi because of diode 14, but since the gate is charged in the normal - connection state, the reverse - connection prevention relay 10 continues to be on. In order to maintain this state, it is desirable to set the resistance value of the resistance element 23 to be high.

[0026] Depending on the conditions of the voltage V BATT , the Zener diode 22 that protects between the gate and the source of the reverse - connection prevention relay 10 may operate. Let the Zener voltage of the Zener diode 22 be Vz, then the gate voltage V GSThis is (=Vz). By setting the Zener voltage Vz to be greater than the threshold voltage Vth1 of the reverse connection prevention relay 10, the reverse connection prevention relay 10 will not turn off.

[0027] Here, in order to keep the reverse connection prevention relay 10 ON when a negative surge is applied, (V GS >The condition Vth1) must be met. When battery 2 is properly connected, the voltage of the power supply VRG is set to satisfy this condition. Voltage V GS This is the gate voltage-source voltage of the reverse-connection prevention relay 10, where the source voltage is the battery voltage V BATT From this state, the voltage will decrease when a negative surge is applied. Then, the voltage V GS Since this voltage becomes large and is likely to exceed the gate-source breakdown voltage of the reverse-connection prevention relay 10, a Zener diode 22 is inserted to prevent this. Therefore, the Zener voltage Vz must satisfy the following conditions. Refer to Figure 6 for the voltages of each part. (Gate-source withstand voltage of reverse-connection prevention relay 10) > Vz > Vth1 …(4)

[0028] Furthermore, when a negative surge is applied, the power supply VRG is not supplied, so it is necessary to maintain the ON state of the reverse connection prevention relay 10 with the charge pre-charged in the gate. A resistor 23 is inserted between the gate and source of the reverse connection prevention relay 10 so that it does not turn on when the ignition switch is turned off. While the ON state of the reverse connection prevention relay 10 is maintained, charge is lost due to the current flowing through the resistor 23 and the leakage current from the diode 14, Zener diode 22, capacitor 24, and relay 10. Therefore, the capacitance value of capacitor 24 is adjusted so that charge does not leave the gate and the reverse connection prevention relay 10 does not turn off during the negative surge application time.

[0029] <Operation upon recovery after the application of negative surge voltage ends> When the application of the negative polarity surge voltage ends, the voltage V BATTBoth voltage IG and voltage VRG return to normal values, power supply to the ECU begins, and power VRG is generated. However, there may be a slight time lag between the end of surge voltage application and the generation of power VRG. In this case, due to the parasitic capacitance of capacitor 24 and reverse connection prevention relay 10, voltage V BATT As the gate voltage V increases, GS It rises in the same way. Therefore, even without a power supply VRG (V GS Since condition Vth1 is satisfied, the reverse connection protection relay 10 will not turn off.

[0030] Here, we consider the constant conditions for each circuit element. The formula for calculating the capacitance C of a capacitor is given by equation (5), where Q is the charge, V is the charging voltage, I is the charging current, and t is the charging time. Q = C × V = I × t …(5) The relationship between the voltages before and after the application of a negative surge is given by equation (6). V GS =(VDi-Vf2)-V BATT >Vth1 …(6) The anode voltage VDi is determined by the voltage VRG, peripheral elements, the on-resistance of the reverse-connection prevention relay 10, the resistance of the resistor 23, and so on.

[0031] When a negative surge is applied, the voltage V GS If the voltage exceeds the gate-source withstand voltage of the reverse-connection prevention relay 10, GS teeth V GS =Vz>Vth1 …(7) Therefore, in order to maintain the ON state of the reverse connection prevention relay 10 when a negative surge is applied, equation (8) must hold true. However, the following voltage V GS This is the voltage immediately after the negative surge is applied. V GS -Vth1=T1×Ir / Co T1 = Co / Ir × (V GS -Vth1) …(8)

[0032] And from equation (6), equation (8) becomes equation (9). T1 = Co / Ir × (VDi - Vf2 - V BATT -Vth1) …(9) Ir: This is the current flowing from point A, which is the gate of the reverse-connection prevention relay 10, and is the current flowing through the resistor 23, the leakage current of the diode 14, and the Zener diode 2 2 This is the sum of the current flowing through the circuit, the leakage current of capacitor 24, the leakage current of reverse-connection prevention relay 10, etc. T1: The negative surge application time plus the time it takes for the power supply VRG voltage to recover. See Figure 7. Co: The capacitance of capacitor 24 plus the parasitic capacitance of reverse-connection prevention relay 10, etc.

[0033] From equation (9), in order to lengthen time T1, the voltage V immediately after the negative surge is applied GS To make it bigger, Increase the voltage VDi. • Reduce the forward voltage Vf2. Increase the Zener voltage Vz. • Reduce the threshold voltage Vth1. • Reduce leakage current. • Increase the capacity Co. This is a possible solution. Additionally, to reduce the current Ir, it is also possible to increase the resistance value of the resistor element 23.

[0034] As described above, according to this embodiment, the power supply reverse connection protection circuit 11 is connected to the inverter circuit 2 that drives the motor 1 and the drive power supply V connected to the inverter circuit 2. BATT The reverse-connection prevention relay 10 is connected between the battery 9 and the power supply point of the inverter circuit 2, and the element drive power supply unit 15 supplies the power VRG generated from the battery 9 to the gate of the reverse-connection prevention relay 10 via the diode 14.

[0035] The reverse polarity protection unit 21 has a transistor 18 connected between the anode of the diode 14 and the connection terminal to which the positive terminal of the battery 9 is connected. When the battery 9 is connected in reverse polarity, the transistor 18 is turned on to form a current path from ground to the connection terminal. Specifically, it is configured to include a second resistive element 16 connected between ground and the anode of the diode 14, a series circuit of a second diode 19 and a third resistive element 10 connected between ground and the base of the transistor 18, and a third diode 17 connected between the anode of the first diode 14 and the collector of the transistor 18.

[0036] As a result, even if a negative surge voltage is applied to the positive terminal of the battery 9, causing the potential of the connection terminal to drop significantly to the negative side, the charge stored in the gate of the reverse-connection prevention relay 10 is discharged through the first resistive element 23, and it remains in the ON state until it falls below the threshold voltage. Therefore, a high voltage is not applied between the conductive terminals of the reverse-connection prevention relay 10, that is, between the connection terminal of the battery 9 and the power supply point 7 of the inverter circuit 2, thereby protecting the reverse-connection prevention relay 10.

[0037] Furthermore, since a capacitor 24 is connected between the connection terminal of the battery 9 and the gate of the reverse connection prevention relay 10, the charge stored in the capacitor 24 allows the reverse connection prevention relay 10 to remain in the ON state for a longer period. In addition, since a Zener diode 22 is connected between the connection terminal and the gate, if a negative surge voltage is applied and the potential of the connection terminal drops significantly, the Zener diode 22 will operate, creating a Zener voltage between the connection terminal and the gate. This provides more reliable protection for the reverse connection prevention relay 10.

[0038] Furthermore, by applying a negative surge voltage to the connection terminals, the time T1 from when the reverse connection prevention relay 10 turns on until it turns off can be set based on equation (9), and the length of time T1 can be adjusted by each calculation parameter in equation (9).

[0039] (Other embodiments) An N-channel MOSFET can be used instead of the NPN transistor 18. Capacitor 24 and Zener diode 22 can be provided as needed. This is not limited to applications to power steering systems.

[0040] This disclosure is described in accordance with the embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the equivalence. In addition, various combinations and forms, as well as other combinations and forms that include only one, more, or fewer of those elements, fall within the scope and concept of this disclosure. [Explanation of symbols]

[0041] In the diagram, 1 is the motor, 2 is the inverter circuit, 7 is the power supply point, 9 is the battery, 10 is the reverse connection prevention relay, 11 is the reverse connection protection circuit, 14 is the first diode, 15 is the power supply unit for driving the element, 16 is the resistive element, 17 is the second diode, 18 is the NPN transistor, 19 is the third diode, 20 is the resistive element, 21 is the reverse connection protection unit, 22 is the Zener diode, 23 is the resistive element, and 24 is the capacitor.

Claims

1. It is connected between a drive circuit (2) that drives a load (1) and a DC power supply (9) that supplies power to this drive circuit. A first protective switching element (10) is connected between the connection terminal of the DC power supply and the power supply point of the drive circuit, The element drive power supply unit (15) supplies the element drive power generated from the DC power supply to the drive terminal of the first protective switching element via a forward first diode (14), A reverse polarity protection unit (21) has a second protective switching element (18) connected between the anode of the first diode and the connection terminal, and when the DC power supply is connected in reverse polarity, the second protective switching element is turned on to form a current path from ground to the connection terminal, A power supply reverse connection protection circuit comprising a first resistive element (23) connected between the connection terminal and the drive terminal.

2. The power supply reverse connection protection circuit according to claim 1, further comprising a capacitor (24) connected between the connection terminal and the drive terminal.

3. The power supply reverse connection protection circuit according to claim 2, further comprising a Zener diode (22) connected between the connection terminal and the drive terminal.

4. If T is the time from when the first protective switching element turns on due to a negative surge voltage being applied to the connection terminal until the first protective switching element turns off, then time T is set based on the following formula. T=C / I×(VDi-Vth-Vf-V ＢＡＴＴ ) C: Capacitance of the capacitor and parasitic capacitance of the first protective switching element I: Current flowing from the drive terminal of the first protective switching element VDi: Anode potential of the first diode Vth: Threshold voltage of the first protective switching element Vf: Forward voltage of the first diode V ＢＡＴＴ : Voltage of the DC power supply The power supply reverse connection protection circuit according to claim 3.

5. The reverse connection protection unit includes a second resistive element (16) connected between ground and the anode of the first diode, A series circuit of a forward-facing second diode (19) and a third resistor (20) connected between ground and the drive terminal of the second protective switching element, A power supply reverse connection protection circuit according to any one of claims 1 to 4, further comprising a forward-facing third diode (17) connected between the anode of the first diode and the second protective switching element.

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