Power supply circuit

Abstract

To provide a power supply circuit capable of detecting heating abnormality caused by a current flowing through a parasitic diode when a reverse connection protective element is in an off-state.SOLUTION: A power supply circuit 201 supplies power from a battery 15 to an inverter circuit (load drive circuit) 60 for driving a motor (load) 80. A reverse connection protective element 52 is composed of a FET having a parasitic diode 527 which conducts a forward current representing a current via the inverter circuit 60 from a positive electrode side of the battery 15 to a negative electrode of the battery 15. An abnormality detection circuit 48 detects heating abnormality of the reverse connection protective element 52 based on a voltage between DSs of a power relay element 51 as "an object element". The power relay element 51 is arranged near the reverse connection protective element 52, and has a characteristic of rising an ON resistance between DSs when a temperature rises by heat transfer from the reverse connection protective element 52. When the heating abnormality of the reverse connection protective element 52 is detected by the abnormality detection circuit 48, electric conduction of the forward current is stopped.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a power supply circuit.

Background Art

[0002] Conventionally, in a power supply circuit that supplies power to a load driving circuit, a technique for protecting circuit elements from overheating is known. For example, in the power supply device disclosed in Patent Document 1, the current flowing through a semiconductor switch provided in a current path is detected based on the drain-source voltage, and the temperature rise of the semiconductor switch is estimated from the square value of the detected current.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] There is a power supply circuit provided with a reverse connection protection element that cuts off a reverse current when the positive and negative electrodes of a battery are connected in the reverse direction to the normal direction. For example, the reverse connection protection element is composed of an FET (field effect transistor) having a parasitic diode that conducts a forward current. When a forward current is passed through in a state where the battery is connected in the normal direction, the reverse connection protection element is basically turned on.

[0005] However, when the reverse connection protection element fails in an OFF stuck state and current continues to flow only through the parasitic diode, there is a risk of heat generation. In this case, the drain-source voltage of the reverse connection protection element is determined by the forward voltage of the parasitic diode. Generally, the drain-source voltage of an FET has a temperature characteristic that increases as the temperature increases, while the voltage drop of the parasitic diode has a temperature characteristic that decreases as the temperature increases. Therefore, it is impossible to detect an abnormal heat generation based on the drain-source voltage of the reverse connection protection element.

[0006] The present invention has been created in view of such points, and its object is to provide a power supply circuit capable of detecting an abnormal heat generation due to a current flowing through a parasitic diode when a reverse connection protection element is OFF.

Means for Solving the Problem

[0007] The present invention One aspect is a power supply circuit that supplies power from a battery (15) to a load driving circuit (60) that drives a load (80), and includes a reverse connection protection element (52) and A power relay element (51) and a power relay opening / closing circuit (41), an abnormality detection circuit (48).

[0008] On the premise that the positive and negative electrodes of the battery are connected in the normal direction, the reverse connection protection element is provided on a power line (Lp) that connects the positive electrode of the battery to the high potential side of the load driving circuit, or on a ground line (Lg) that connects the negative electrode of the battery to the low potential side of the load driving circuit. The reverse connection protection element is composed of a field effect transistor having a parasitic diode (527) that conducts a forward current, which is a current flowing from the positive electrode side of the battery through the load driving circuit toward the negative electrode of the battery. The power relay element is provided on a power line and is composed of a field effect transistor having a parasitic diode (517) that conducts a reverse current, which is a current flowing from the high potential side of the load driving circuit toward the positive electrode of the battery. The power relay opening / closing circuit performs an ON / OFF operation on the power relay element.

[0009] The abnormality detection circuit detects an abnormal heat generation of the reverse connection protection element based on the drain-source voltage of the "target element". The target element is an element composed of a field effect transistor arranged in the vicinity of the reverse connection protection element, and has a characteristic that the ON resistance between the drain and the source increases when the temperature rises due to heat transfer from the reverse connection protection element.

[0010] "In the vicinity of the reverse connection protection element" means a range in which heat transfer from the reverse connection protection element is considered to be sufficient based on the common general knowledge in the technical field. 。

[0011] When the abnormality detection circuit detects an abnormal heat generation of the reverse connection protection element, The power relay opening / closing circuit shuts off the power relay element, the energization of the forward current is stopped. In one aspect, the target element is the power relay element. In another aspect of the present invention, the target element may be an element constituting a load driving circuit such as an inverter circuit.

[0012] In the present invention, paying attention to the fact that the target element arranged near the reverse connection protection element increases in temperature due to heat transfer from the reverse connection protection element, the heat generation of the reverse connection protection element is indirectly detected based on an increase in the drain-source voltage of the target element. Thereby, it is possible to detect an abnormal heat generation due to a forward current flowing through the parasitic diode when the reverse connection protection element is OFF. For example, when an abnormal heat generation is detected even though an ON signal is commanded to the reverse connection protection element, it can be estimated that it is an OFF sticking failure.

[0013] Also, when an abnormal heat generation of the reverse connection protection element is detected by the abnormality detection circuit, the energization of the forward current is stopped, so that the reverse connection protection element and the entire circuit can be protected from overheating.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0015] Multiple embodiments of the power supply circuit of the present invention will be described with reference to the drawings. The "present embodiment" includes the first to third embodiments. In the present embodiment, the "load" is the motor 80, specifically a three-phase AC motor, and the "load drive circuit" is the inverter circuit 60. The power supply circuit supplies power from the battery 15 to the inverter circuit 60 that drives the motor 80. For example, the motor 80 is a motor for a vehicle's control brake, and the battery 15 is an in-vehicle battery of about 12V.

[0016] The reference numeral of the power supply circuit in each embodiment is suffixed with the embodiment number in the third digit following "20". In the description of the embodiments, the field effect transistor is referred to as "FET", and the drain-source interval is referred to as "DS interval". Also, in the figures, the drain is denoted as "D", the source is denoted as "S", the switching circuit and the switching signal are denoted as "SW circuit" and "SW signal", respectively. The FET used in the present embodiment is an N-channel MOSFET (metal oxide semiconductor field effect transistor).

[0017] (First Embodiment) With reference to FIGS. 1 to 3, the power supply circuit 201 of the first embodiment will be described. As shown in FIG. 1, the power supply circuit 201 includes a power relay element 51 and a reverse connection protection element 52 provided in the power supply path from the battery 15 to the inverter circuit 60, opening / closing circuits 41 and 42 for performing ON / OFF operations on the respective elements 51 and 52, and an abnormality detection circuit 48 for detecting an abnormality of the reverse connection protection element 52.

[0018] On the premise that the positive and negative electrodes of the battery 15 are connected in the normal direction, the power line Lp connects the positive electrode of the battery 15 and the high potential side of the inverter circuit 60. The ground line Lg connects the negative electrode of the battery 15 and the low potential side of the inverter circuit 60. In the first embodiment, the power relay element 51 is provided on the battery 15 side in the power line Lp, and the reverse connection protection element 52 is provided on the inverter circuit 60 side in the power line Lp.

[0019] The power relay element 51 and the reverse connection protection element 52 are composed of FETs. The drain of the power relay element 51 is connected to the positive electrode side of the battery 15, and the source is connected to the reverse connection protection element 52. The parasitic diode 517 of the power relay element 51 conducts the reverse current, which is the current flowing from the high potential side of the inverter circuit 60 towards the positive electrode of the battery 15.

[0020] The drain of the reverse connection protection element 52 is connected to the high potential side of the inverter circuit 60, and the source is connected to the power relay element 51. The parasitic diode 527 of the reverse connection protection element 52 conducts the forward current, which is the current flowing from the positive electrode of the battery 15 through the inverter circuit 60 towards the negative electrode of the battery 15. When the positive and negative electrodes of the battery 15 are accidentally connected in the opposite direction to the normal direction, if the reverse connection protection element 52 is OFF, no reverse current will flow from the low potential side to the high potential side of the inverter circuit 60, and the inverter circuit 60 is protected.

[0021] The power relay opening / closing circuit 41 and the reverse connection protection element opening / closing circuit 42 perform ON / OFF operations on the power relay element 51 and the reverse connection protection element 52 respectively according to the commands from the control unit 40. The control unit 40 is composed of, for example, a microcomputer, and controls the operations of the power relay opening / closing circuit 41, the reverse connection protection element opening / closing circuit 42, the inverter element switching circuit 46, etc. based on the commands from the upper vehicle control circuit. The abnormality detection circuit 48 detects the voltage Vds between the drain and source of the power relay element 51, and detects the heat generation abnormality of the reverse connection protection element 52 based on the voltage Vds between the drain and source. The principle will be described later.

[0022] The inverter circuit 60 has six inverter elements 61 - 66 composed of FETs connected in a bridge configuration. The inverter elements 61, 62, and 63 are the upper arm elements of the U-phase, V-phase, and W-phase, and the inverter elements 64, 65, and 66 are the lower arm elements of the U-phase, V-phase, and W-phase. In the circuit example of FIG. 1, shunt resistors 71, 72, and 73 for detecting the phase current are connected to the low potential side of the lower arm elements 64, 65, and 66. By operating the inverter elements 61 - 66 according to the switching signal from the inverter element switching circuit 46, the DC power of the battery 15 is converted into three-phase AC power and supplied to the motor 80.

[0023] In such a circuit, from the perspective of fail-safe, it is required to detect element failures during initial checks and normal operation. Generally, since the voltage between the drain and source of an FET has a temperature characteristic that increases as the temperature rises, it is possible to detect overheating abnormalities in the ON state of the FET as in the prior art of Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2009 - 142146). On the other hand, since the voltage drop of the parasitic diode has a temperature characteristic that decreases as the temperature rises, when the reverse connection protection element 52 fails in an OFF-stuck state and current continues to flow only through the parasitic diode 527 and generates heat, it is impossible to detect heat generation abnormalities based on the voltage between the drain and source.

[0024] Therefore, in the present embodiment, an element composed of an FET arranged in the vicinity of the reverse connection protection element 52 is defined as the "target element". The target element has a characteristic that the ON resistance between the drain and source increases when the temperature rises due to heat transfer from the reverse connection protection element 52. The abnormality detection circuit 48 indirectly detects the heat generation abnormality of the reverse connection protection element 52 by detecting the voltage between the drain and source of the target element whose temperature has risen due to heat transfer. When heat is generated despite the reverse connection protection element 52 being in the ON operation, it is presumed that a forward current continues to flow only through the parasitic diode 527 due to an OFF-stuck failure.

[0025] In the first embodiment, a power relay element 51 is used as the target element. The power relay element 51 is arranged in the vicinity of the reverse connection protection element 52 and its temperature rises due to heat transfer from the reverse connection protection element 52. It is assumed that it has been confirmed by initial check or the like that the power relay element 51 itself is normal.

[0026] When the abnormality detection circuit 48 detects an abnormal heat generation of the reverse connection protection element 52 based on the voltage Vds between the drain and source of the power relay element 51, it outputs a cutoff signal to the power relay opening / closing circuit 41 to cut off the power relay element 51. As a result, the flow of the forward current flowing through the parasitic diode 527 of the reverse connection protection element 52 is stopped.

[0027] In addition, when the abnormality detection circuit 48 detects an abnormal heat generation of the reverse connection protection element 52, it notifies the control unit 40. The control unit 40 that has received the notification may output a drive stop signal to the inverter element switching circuit 46. Also, the user (the driver in the case of a vehicle) may be notified of the abnormality by an alarm display or a buzzer.

[0028] Fig. 2 shows a preferred configuration example in which the power relay element 51, which is the target element, is arranged in the vicinity of the reverse connection protection element 52 in order to obtain good heat transfer characteristics. In the example shown in Fig. 2(a), the power relay element 51 and the reverse connection protection element 52 are mounted adjacent to each other on the same surface (surface 31) of the substrate 30. In the example shown in Fig. 2(b), the power relay element 51 and the reverse connection protection element 52 are mounted on the surface 31 and the back surface 32 at the same location of the substrate 30. The heat generated by the reverse connection protection element 52 is transferred to the power relay element 51 on the opposite side across the substrate 30.

[0029] In the example shown in Fig. 2(c), the power relay element 51 and the reverse connection protection element 52 are housed in the same package of the element module 500. In this configuration, while heat transfer to peripheral elements is suppressed, heat is actively transferred from the reverse connection protection element 52 to the power relay element 51 within the package.

[0030] The flowchart of FIG. 3 shows the abnormality detection process according to the first embodiment. In the description of the flowchart, the symbol "S" means step. In S11, the control unit 40 turns on the power relay element 51 and the reverse connection protection element 52 by the power relay opening / closing circuit 41 and the reverse connection protection element opening / closing circuit 42. In S12, the driving of the inverter circuit 60 is started by the inverter element switching circuit 46, and power is supplied to the motor 80.

[0031] In S13, the abnormality detection circuit 48 determines whether the voltage Vds between the drain and source of the power relay element 51, which is the target element, is greater than the threshold value. If YES in S13, in S14, the abnormality detection circuit 48 outputs a cutoff signal to the power relay opening / closing circuit 41. The power relay opening / closing circuit 41 that has received the cutoff signal cuts off the power relay element 51. As a result, the energization of the forward current flowing through the parasitic diode 527 of the reverse connection protection element 52 is stopped. Note that the control unit 40 that has received the notification from the abnormality detection circuit 48 may output a cutoff signal to the power relay opening / closing circuit 41, but by directly outputting a cutoff signal from the abnormality detection circuit 48 to the power relay opening / closing circuit 41, more rapid measures can be taken.

[0032] Furthermore, as an arbitrary step, in S15, the control unit 40 that has received the notification from the abnormality detection circuit 48 may output a drive stop signal to the inverter element switching circuit 46 to stop the driving of the inverter circuit 60. Thereby, it is avoided that the operation of the inverter circuit 60 continues after the power supply is stopped. If NO in S13, the process ends.

[0033] As described above, the abnormality detection circuit 48 of the first embodiment detects that the reverse connection protection element 52 is generating heat despite being turned on, based on the voltage Vds between the drain and source of the power relay element 51, which is the target element, and estimates that it is an OFF sticking failure of the reverse connection protection element 52. Therefore, it is possible to detect the abnormal heat generation of the reverse connection protection element 52 during normal operation. Also, by cutting off the power relay element 51 at the time of abnormality detection to stop the energization of the forward current, the reverse connection protection element 52 and the entire circuit can be protected from overheating.

[0034] (Second Embodiment) Referring to FIGS. 4 and 5, the power supply circuit 202 of the second embodiment will be described. In the second embodiment, a power relay element is not provided on the power line Lp. When the external power switch 16 provided between the positive electrode of the battery 15 and the power supply circuit 202 is in the ON state, the voltage of the battery 15 is constantly applied to the inverter circuit 60. For example, in a system mounted on a vehicle, the ignition switch corresponds to the external power switch 16.

[0035] In the second embodiment, any one or more elements (FETs) constituting the inverter circuit 60 are used as the target element. Basically, it is preferable that the element that is arranged closest to the reverse connection protection element 52 on the substrate and has the largest heat transfer amount is selected as the target element. Also, points such as the element itself being thermally stable and being less susceptible to disturbances from other heat sources are the points for selecting the target element.

[0036] In the example shown in FIG. 4, the U-phase upper arm element 61 is the target element. The abnormality detection circuit 48 detects the heat generation abnormality of the reverse connection protection element 52 based on the voltage Vds between the D and S terminals of the U-phase upper arm element 61. It is assumed that it has been confirmed through an initial check or the like that the inverter elements 61 - 66 themselves are normal.

[0037] The flowchart of FIG. 5 shows the abnormality detection process according to the second embodiment. Each step number S21, S22, S23, S25 in FIG. 5 corresponds to S11, S12, S13, S15 in FIG. 3. In S21, the control unit 40 turns on the reverse connection protection element 52 by the reverse connection protection element opening / closing circuit 42. In S22, the driving of the inverter circuit 60 is started by the inverter element switching circuit 46, and power is supplied to the motor 80.

[0038] In S23, the abnormality detection circuit 48 determines whether the voltage Vds between the drain and source of the inverter element 61, which is the target element, is greater than the threshold value. If the result in S23 is YES, the control unit 40 that has received the notification from the abnormality detection circuit 48 outputs a drive stop signal to the inverter element switching circuit 46 in S25 to stop the drive of the inverter circuit 60. As a result, the energization of the forward current flowing through 527 of the reverse connection protection element 52 is stopped. If the result in S23 is NO, the process ends.

[0039] In this way, even when the element of the inverter circuit 60 is used as the target element, the same operational effects as those of the first embodiment can be obtained. The target element is not limited to the U-phase upper arm element 61, and may be the V-phase or W-phase upper arm elements 62, 63. Alternatively, the voltages Vds between the drain and source of each of the upper arm elements 61, 62, 63 may be detected, and an abnormality may be detected based on the maximum value thereof.

[0040] (Third Embodiment) Referring to FIG. 6, the power supply circuit 203 of the third embodiment will be described. In the third embodiment, a reverse connection protection element 52 is provided on the ground line Lg that connects the negative electrode of the battery 15 and the low potential side of the inverter circuit 60. In this configuration, for the reverse connection protection element 52, the drain is connected to the negative electrode side of the battery 15, and the source is connected to the low and high potential sides of the inverter circuit 60. The point that the parasitic diode 527 conducts the forward current is the same.

[0041] Similar to the first embodiment, in the third embodiment, the power supply relay element 51 is used as the target element. The power supply relay element 51 is arranged in the vicinity of the reverse connection protection element 52 and its temperature rises due to heat transfer from the reverse connection protection element 52. The operations of the abnormality detection circuit 48 and the power supply relay opening / closing circuit 41 are the same as those in the first embodiment. The same operational effects as those of the first embodiment can also be obtained in the third embodiment.

[0042] (Other Embodiments) (a) The load is not limited to a polyphase motor such as a three-phase motor, and may be a DC motor or an actuator other than a motor. The load drive circuit is not limited to an inverter circuit, and may be an H-bridge circuit or the like.

[0043] (b) In the second embodiment, assuming a circuit configuration without a power relay element, the elements constituting the load drive circuit are used as target elements. However, even in a circuit configuration with a power relay element, depending on the heat transfer characteristics from the reverse connection protection element, the elements constituting the load drive circuit may be preferentially selected as target elements. Alternatively, both the power relay element and the elements constituting the load drive circuit may be used as target elements.

[0044] As described above, the present invention is not limited to such embodiments, and can be implemented in various forms without departing from the spirit thereof.

Explanation of Reference Numerals

[0045] 15 ··· Battery 201 - 203 ··· Power supply circuit 41 ··· Power relay opening / closing circuit 48 ··· Abnormality detection circuit 51 ··· Power relay element, 517 ··· Parasitic diode 52 ··· Reverse connection protection element, 527 ··· Parasitic diode 60 ··· Inverter circuit (load drive circuit) 80 ··· Motor (load) Lp ··· Power line, Lg ··· Ground line.

Claims

1. A power supply circuit that supplies power from a battery (15) to a load driving circuit (60) for driving a load (80), Assuming that the positive and negative electrodes of the battery are connected in the normal direction, a power line (Lp) connecting the positive electrode of the battery and the high potential side of the load driving circuit, or a ground line (Lg) connecting the negative electrode of the battery and the low potential side of the load driving circuit, and a parasitic diode (527) that conducts a forward current, which is a current flowing from the positive electrode of the battery through the load driving circuit to the negative electrode of the battery, and is composed of a field effect transistor having the parasitic diode; A power supply relay element (51) provided on the power line and composed of a field effect transistor having a parasitic diode (517) that conducts a reverse current, which is a current flowing from the high potential side of the load driving circuit toward the positive electrode of the battery; A power supply relay opening / closing circuit (41) for ON / OFF operating the power supply relay element; An element composed of a field effect transistor arranged in the vicinity of the reverse connection protection element, and for a target element having a characteristic that the ON resistance between the drain and source increases when the temperature rises due to heat transfer from the reverse connection protection element, an abnormality detection circuit (48) for detecting an abnormal heat generation of the reverse connection protection element based on the drain-source voltage of the target element; comprising: When the abnormality detection circuit detects an abnormal heat generation of the reverse connection protection element, the power supply relay opening / closing circuit shuts off the power supply relay element, and the conduction of the forward current is stopped, The target element is the power supply relay element, which is the power supply circuit.

2. A power supply circuit that supplies power from a battery (15) to a load driving circuit (60) for driving a load (80), On the premise that the positive electrode and the negative electrode of the battery are connected in the normal direction, a power line (Lp) connecting the positive electrode of the battery and the high-potential side of the load driving circuit, or a ground line (Lg) connecting the negative electrode of the battery and the low-potential side of the load driving circuit is provided, and a parasitic diode (527) that conducts a forward current, which is a current flowing from the positive electrode of the battery through the load driving circuit toward the negative electrode of the battery, is provided. The reverse connection protection element (52) is composed of a field effect transistor having An element composed of a field effect transistor arranged in the vicinity of the reverse connection protection element. When the temperature rises due to heat transfer from the reverse connection protection element, an abnormal detection circuit (48) that detects an abnormal heat generation of the reverse connection protection element based on the drain-source voltage of the target element having a characteristic that the ON resistance between the drain and the source increases is provided with When the abnormal detection circuit detects an abnormal heat generation of the reverse connection protection element, the energization of the forward current is stopped. The target element is a power supply circuit that is an element constituting the load driving circuit.

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