JP2018157272A - Electronic device for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic device for vehicle capable of improving detection accuracy of an open-circuit failure in a protective MOS transistor with respect to a temperature change.SOLUTION: An electronic device for vehicle comprises a protective MOS transistor for reverse connection protection at a low side that is a reference potential side with respect to a load. The protective MOS transistor is configured to form a parasitic diode in a forward direction toward a reference potential, and comprises a temperature compensation circuit which is provided in series with the diode, between a high-side first connection point and a second connection point that is closer to the reference potential than the protective MOS transistor. The temperature compensation circuit has the same temperature property as the parasitic diode and is mounted so as to be mutually thermally coupled with the parasitic diode, such that electrification between the first connection point and the second connection point is controlled depending on a forward voltage of the parasitic diode. Based on a potential at a connection point between the first connection point and the temperature compensation circuit, an open-circuit failure of a gate in the protective MOS transistor is detected.SELECTED DRAWING: Figure 1

Description

  The disclosure of this specification relates to an electronic device for a vehicle provided with a protection circuit against reverse connection of a power source.

  When a power source is supplied to a load such as an inverter, a protection MOS transistor is known as a protection against reverse connection of the power source. When the power supply is normally connected, a gate voltage resulting from the power supply is applied to the gate of the protection MOS transistor to turn it on, and supply a current to the load. On the other hand, when the power supply is reversely connected, the protection MOS transistor is turned off so that no current flows through the load.

  By the way, an open failure of the gate of the protection MOS transistor and a situation where an appropriate potential is not applied to the gate are assumed. In this state, no gate voltage is applied even if the power supply is normally connected. For this reason, the protection MOS transistor is kept off, and the parasitic diode between the source and the drain is energized. When the parasitic diode is energized, the protection MOS transistor is overheated, and thus detection of an open failure of the protection MOS transistor is required.

  Patent Document 1 discloses a technique for detecting an open failure based on a source-drain voltage of a protection MOS transistor. When the power supply is normally connected in a state where an open failure has occurred in the gate of the protection MOS transistor, a potential difference corresponding to the forward voltage Vf of the parasitic diode is generated between the source and the drain. Therefore, an open failure can be detected using the forward voltage Vf at a predetermined temperature as a threshold value.

JP-A-2015-61338

  However, since the forward voltage Vf of the parasitic diode has a negative temperature characteristic, Vf decreases as the temperature increases. That is, even if a typical value of Vf is set as the threshold value, the source-drain voltage becomes lower than the threshold value in a high temperature state, and an open failure may not be detected.

  In view of the above problems, an object of the present disclosure is to provide an electronic device that can improve the detection accuracy of an open failure of a protection MOS transistor against a change in temperature.

  The invention disclosed herein employs the following technical means to achieve the above object. Note that the reference numerals in parentheses described in the claims and in this section indicate a corresponding relationship with specific means described in the embodiments described later as one aspect, and limit the technical scope of the invention. Not what you want.

  In order to achieve the above object, the vehicle electronic device disclosed in this specification is provided on the low side that is the reference potential side with respect to the load, and the voltage on the high side that is the power supply side with respect to the load is A vehicular electronic device including a protection MOS transistor for reverse connection protection applied to a gate, wherein the protection MOS transistor is formed with a parasitic diode that is forward directed toward a reference potential, A temperature compensation circuit provided in series with the diode is provided between the first connection point on the high side and the second connection point on the reference potential side of the protection MOS transistor, and the temperature compensation circuit includes a temperature of the parasitic diode. The first connection point and the second connection point are implemented by having a temperature characteristic that reduces the characteristic difference and being thermally coupled to the parasitic diode. Is controlled so as to depend on the forward voltage of the parasitic diode, and an open failure of the gate of the protection MOS transistor is detected based on the potential of the connection point between the first connection point and the temperature compensation circuit. .

  According to this, the temperature compensation circuit has the same temperature characteristic as the parasitic diode, and is mounted so as to be thermally coupled to the parasitic diode. Thereby, the presence / absence of energization between the first connection point and the second connection point is controlled to depend on the forward voltage of the parasitic diode. Therefore, even if the forward voltage of the parasitic diode fluctuates depending on the temperature due to overheating, the presence or absence of an open failure of the protection MOS transistor is detected by the presence or absence of current from the first connection point to the second connection point. can do.

It is a circuit diagram which shows schematic structure of the electronic device for vehicles which concerns on 1st Embodiment. It is a figure which shows the temperature characteristic of the voltage between base-emitters, and the temperature characteristic of a forward voltage. It is a figure which shows mounting of a protection MOS transistor and a temperature compensation circuit (bipolar transistor). It is a figure which shows the ground current dependence of the electric potential of the source terminal of a protection MOS transistor, and the electric potential of the collector terminal of a bipolar transistor. It is a circuit diagram which shows schematic structure of the electronic device for vehicles which concerns on a modification. It is a circuit diagram which shows schematic structure of the electronic device for vehicles which concerns on other embodiment.

  Hereinafter, a plurality of modes for carrying out the present disclosure will be described with reference to the drawings. In each embodiment, parts corresponding to the matters described in the preceding embodiment may be denoted by the same reference numerals, and redundant description may be omitted. When only a part of the configuration is described in each mode, the other modes described above can be applied to the other parts of the configuration. Not only combinations of parts that clearly indicate that combinations are possible in each form, but also forms may be partially combined even if they are not clearly specified, as long as there is no problem with the combination. Is possible.

(First embodiment)
Initially, with reference to FIGS. 1-3, schematic structure of the vehicle electronic device which concerns on this embodiment is demonstrated.

  As shown in FIG. 1, this vehicular electronic device 100 is a device that supplies power to a load 200 such as an inverter, for example, and includes a power supply line La connected to a power supply potential VB and a reference connected to a reference potential GND. A load 200 is provided in parallel with the line Lb.

  The vehicular electronic device 100 is a protection circuit for preventing and protecting the power supply to the load 200 against unintended reverse connection of a power source, and includes a protection MOS transistor 10. In addition, the vehicle electronic device 100 includes a temperature compensation circuit 20 and an abnormality detection comparator 30.

  The protection MOS transistor 10 is an N-channel MOS transistor, and has a parasitic diode 11 in the forward direction from the source to the drain. The protection MOS transistor 10 has a source terminal connected to the load 200 and a drain terminal connected to the reference potential GND on the reference line Lb. In other words, the protection MOS transistor 10 is provided on the low side with respect to the load 200. The gate terminal of the protection MOS transistor 10 is connected to the power supply line La via the resistor 31. That is, a voltage on the high side with respect to the load 200 is applied to the gate terminal via the resistor 31.

  When the power supply is normally connected, the potential of the gate terminal of the protection MOS transistor 10 becomes higher than the potential of the drain terminal, and the protection MOS transistor 10 is turned on when a potential difference equal to or higher than the threshold voltage is generated. As a result, conduction between the source and drain is established, and the prescribed power is supplied to the load 200.

  On the other hand, when the power supply is reversely connected, the potential of the gate terminal of the protection MOS transistor 10 becomes lower than the potential of the drain terminal, and the protection MOS transistor 10 is not turned on. Therefore, no current is supplied to the load 200. As a result, unintended power supply to the load 200 can be prevented, and the circuit and the like constituting the load 200 can be protected.

  The parasitic diode 11 has an IV characteristic according to a general diode, and a forward voltage Vf is defined. It is assumed that an open failure has occurred at the gate terminal of the protection MOS transistor 10. That is, it is assumed that an abnormality has occurred in which the protection MOS transistor 10 is always turned off regardless of whether or not a voltage is applied to the gate terminal. At this time, even if the power supply is normally connected, the protection MOS transistor 10 is not turned on, and if the source-drain voltage exceeds the forward voltage Vf, the current supplied from the power supply passes through the parasitic diode 11. The protective MOS transistor 10 flows. The forward voltage Vf of the parasitic diode 11 has a negative temperature characteristic, and the forward voltage Vf decreases as the temperature of the parasitic diode 11 increases.

  A capacitor 32 and a Zener diode 33 are connected in parallel between the gate and source of the protection MOS transistor 10. The zener diode 33 is forward in the direction from the source terminal to the gate terminal of the protection MOS transistor 10. The capacitor 32 and the Zener diode 33 are inserted for the purpose of suppressing fluctuations in the gate voltage against electrical noise such as surge.

  The temperature compensation circuit 20 is connected between the first connection point P on the power line La on the high side with respect to the load 200 and the second connection point Q on the reference line Lb on the low side. The second connection point Q is located on the side opposite to the load 200 with respect to the protection MOS transistor 10 and has the same potential as the drain terminal of the protection MOS transistor 10. A resistor 34 and a diode 35 are interposed between the first connection point P and the temperature compensation circuit 20. The diode 35 is forward in the direction from the first connection point P to the second connection point Q. Thus, between the first connection point P and the second connection point Q, the resistor 34, the diode 35, and the temperature compensation circuit 20 are connected in series in this order. This series circuit is parallel to the load 200.

  As shown in FIG. 1, the temperature compensation circuit 20 in this embodiment includes an NPN-type bipolar transistor 21. The collector terminal of the bipolar transistor 21 is connected to the cathode terminal of the diode 35, the emitter terminal is connected to the second connection point Q (in other words, the drain terminal of the protection MOS transistor 10), and the base terminal is connected via the resistor 36. And connected to the source terminal of the protection MOS transistor 10. The bipolar transistor 21 corresponds to the compensating bipolar transistor described in the claims.

The junction saturation voltage V _BE between the base and the emitter of the bipolar transistor 21 has the same temperature characteristic as that of the parasitic diode 11 of the protection MOS transistor 10 as shown in FIG. That is, the junction saturation voltage V _BE between the base and the emitter of the bipolar transistor 21 has a negative temperature characteristic and decreases as the temperature increases. The bipolar transistor 21 functions as a switching element in which current flows between the collector and the emitter when the base terminal reaches a potential exceeding the junction saturation voltage V _BE .

  The abnormality detection comparator 30 has a collector terminal of the bipolar transistor 21 connected to one input terminal. The other input terminal is connected to the emitter terminal of the bipolar transistor 21, that is, the drain terminal of the protection MOS transistor 10. That is, the abnormality detection comparator 30 compares the potential at the collector terminal of the bipolar transistor 21 with the potential at the second connection point Q. Based on the output of the abnormality detection comparator 30, the presence or absence of an open failure of the protection MOS transistor 10 is determined.

  The vehicle electronic device 100 according to the present embodiment includes a terminal connected to the first connection point P side in the temperature compensation circuit 20, that is, a collector terminal of the bipolar transistor 21 and a second connection point Q. A Zener diode 37 having an anode on the second connection point side is provided. The Zener diode 37 is an element that protects the potential difference between the two abnormality detection comparators 30 from exceeding a predetermined voltage.

  By the way, the bipolar transistor 21 and the protection MOS transistor 10 in this embodiment are mounted so as to be thermally coupled to each other. Specifically, as shown in FIG. 3, the bipolar transistor 21 and the protection MOS transistor 10 are mounted on the printed circuit board 300 close to each other. The emitter terminal of the bipolar transistor 21 is connected to a copper land 301. The drain terminals of the protection MOS transistor 10 having the same potential as that of the emitter terminal are connected to the copper land 301 so that they have the same temperature. Although the specific mounting form is not ask | required, it is preferable to mount so that the parasitic diode 11 of the protection MOS transistor 10 and the base-emitter junction of the bipolar transistor 21 may have the same temperature as much as possible.

  Next, with reference to FIG. 4, the effect by employ | adopting the vehicle electronic device 100 in this embodiment is demonstrated.

  Assume an abnormality in which the gate of the protection MOS transistor 10 has an open failure and is always in an off state. At this time, when the power supply is normally connected, a current flows from the power supply potential VH to the reference potential GND through the parasitic diode 11. This is called a ground current. When the ground current flows, the potential difference between the anode and the cathode of the parasitic diode 11 is the forward voltage Vf. That is, when the second connection point Q is used as a reference, the potential of the source terminal of the protection MOS transistor 10 is Vf. Vf is substantially constant with respect to the ground current, but slightly increases as the ground current increases, as shown in FIG. Further, as shown in FIG. 2, Vf has a negative temperature characteristic. Therefore, Vf decreases as the temperature increases. That is, the potential of the source terminal of the protection MOS transistor 10 decreases as the temperature increases.

Since the source terminal of the protection MOS transistor 10 is connected to the base terminal of the bipolar transistor 21 which is the temperature compensation circuit 20 via the resistor 36, the potential of the source terminal of the protection MOS transistor 10 is the base terminal of the bipolar transistor 21. Determine the potential. Here, since the junction saturation voltage V _BE between the base and the emitter has the same negative temperature characteristic as that of the parasitic diode 11, the potential of the base terminal for allowing a current to flow between the collector and the emitter decreases as the temperature increases. .

  As described above, even if the potential of the source terminal of the protection MOS transistor 10 (that is, the forward voltage Vf) becomes smaller as the temperature rises, the voltage of the base terminal related to the conduction between the collector and the emitter of the bipolar transistor 21 also increases. It decreases together. Therefore, in the vehicle electronic device 100 of the present embodiment, as shown in FIG. 4, when a predetermined ground current Ith flows through the parasitic diode 11 without depending on the temperature, the collector terminal of the bipolar transistor 21 A drop in potential will be observed.

  The abnormality detection comparator 30 in the vehicular electronic device 100 has a potential difference between the collector terminal of the bipolar transistor 21 and the potential of the second connection point Q being substantially zero. A message to that effect is output to an external control unit (not shown). The control unit can detect an open failure of the protection MOS transistor 10 based on this signal. As described above, since the value Ith of the ground current for detection does not depend on the temperature, the vehicle electronic device 100 can improve the detection accuracy of the open failure of the protection MOS transistor 10 against a change in temperature.

  For the processing after detection, for example, fail-safe control such as stopping the supply of the power supply potential VB is effective. When such control is performed, a filter time of a predetermined time may be provided for the output signal of the abnormality detection comparator 30 in order to prevent oscillation due to repeated stop and return of the supply of the power supply potential VB. It is preferable to execute fail-safe control when the abnormality detection comparator 30 continuously outputs an output signal associated with an open failure of the protection MOS transistor 10 for more than the filter time.

(Modification)
By the way, the temperature compensation circuit 20 is not limited to the bipolar transistor 21 as in the above-described embodiment. It is only necessary that the characteristic that triggers the energization of the first connection point P and the second connection point Q has the same temperature characteristics as the parasitic diode 11.

  For example, as shown in FIG. 5, MOSFET 22 can be employed instead of bipolar transistor 21. The MOSFET 22 has the same temperature characteristic of the threshold voltage Vth as that of the parasitic diode 11.

  Even in such a mode, as in the first embodiment, the MOSFET 22 is turned on and a decrease in the potential of the drain terminal is observed when a predetermined ground current Ith flows through the parasitic diode 11 without depending on the temperature. be able to. That is, an open failure of the protection MOS transistor 10 can be detected.

(Other embodiments)
The preferred embodiment has been described above, but the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist disclosed in this specification.

  In the embodiment and the modification described above, the example in which the Zener diode 37 that protects the two potential input terminals of the abnormality detection comparator 30 from being excessively charged is inserted. However, the Zener diode 37 is not necessarily required. However, it may be omitted depending on mounting restrictions on the printed circuit board 300 and the like.

  In the embodiment and the modification described above, the abnormality detection comparator 30 is used to compare the potential of the collector terminal of the bipolar transistor 21 or the drain terminal of the MOSFET 22 with the potential of the second connection point Q, thereby protecting MOS. An example of detecting an open failure of the transistor 10 has been described. However, essentially, it is only necessary to monitor the potential of the terminal on the first connection point P side in the temperature compensation circuit 20, and for example, as shown in FIG. 6, the first connection point P side in the temperature compensation circuit 20 is used. The terminal potential may be directly output to a microcomputer or the like. In such an aspect, for example, a Zener diode 38 is inserted between the source terminal of the protection MOS transistor 10 and the potential of the terminal on the first connection point P side in the temperature compensation circuit 20, so that the first in the temperature compensation circuit 20. A configuration that prevents an unintended increase in potential of the terminal on the connection point P side is preferable.

  Further, the temperature characteristics of the parasitic diode 11 and the temperature compensation circuit 20 do not need to be completely matched, and corresponding characteristic values V (for example, the junction saturation voltage between the base and the emitter in the bipolar transistor 21 and the threshold voltage in the MOSFET 22). ), It is only necessary that | ΔV−ΔVf | / ΔT be smaller than ΔVf / ΔT. More preferably, ΔV / ΔT may be the same as ΔVf / ΔT of the forward voltage in the parasitic diode 11, that is, | ΔV−ΔVf | / ΔT = 0.

DESCRIPTION OF SYMBOLS 10 ... Protection MOS transistor, 11 ... Parasitic diode, 20 ... Temperature compensation circuit, 21 ... Bipolar transistor

Claims (4)

For a vehicle provided with a protection MOS transistor for reverse connection protection provided on a low side which is a reference potential side with respect to a load, and a voltage on a high side which is a power supply side with respect to the load is applied to a gate An electronic device,
The protection MOS transistor is formed with a parasitic diode that is forward toward the reference potential.
A temperature compensation circuit provided in series with a diode between the first connection point on the high side and the second connection point on the reference potential side of the protection MOS transistor;
The temperature compensation circuit is mounted so as to have a temperature characteristic that reduces a temperature characteristic difference between the parasitic diodes and to be thermally coupled to the parasitic diode, whereby the first connection point and the first The energization between the two connection points is controlled to depend on the forward voltage of the parasitic diode;
An electronic device for a vehicle in which an open failure of the gate of the protection MOS transistor is detected based on a potential at a connection point between the first connection point and the temperature compensation circuit.   The vehicle electronic device according to claim 1, wherein the temperature compensation circuit has the same temperature characteristics as the parasitic diode. The temperature compensation circuit includes a compensation bipolar transistor,
A collector terminal of the compensating bipolar transistor is connected to the first connection point side;
An emitter terminal is connected to the second connection point;
A base terminal is connected to a third connection point between the protection MOS transistor and the load,
The vehicle electronic device according to claim 1, wherein a base-emitter voltage has a temperature characteristic identical to a temperature characteristic of a forward voltage in the parasitic diode.   4. The device according to claim 1, further comprising a Zener diode having an anode on the second connection point side between a terminal connected to the first connection point side in the temperature compensation circuit and the second connection point. The vehicle electronic device according to claim 1.

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