JP2000231417A - Overheat diagnostic device for field effect transistor in electric apparatus driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely and exactly diagnose the overheating state of a field effect transistor caused by the lock of electric apparatus with a simple configuration without increasing cost in an electric equipment driving circuit in which a field effect transistor and electric equipment are connected in series between a power source and ground. SOLUTION: A reference voltage setting means 5 sets a reference voltage corresponding to a set temperature preliminarily set based on lock currents which are allowed to run according to the lock of electric equipment 3 and the temperature and ON resistance characteristics of a field effect transistor 2. A comparing means 8 compares the reference voltage set by the reference voltage setting means 5 with a voltage at a node 9 of the field effect transistor 2 and the electric equipment 3. A judging means 10 judges the overheat of the field effect transistor 2 based on a signal output from the comparing means 8 when the voltage of the node 9 becomes the reference voltage or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric device driving circuit in which a field effect transistor and an electric device are connected in series between a power supply and a ground. Field of the Invention The present invention relates to a device for diagnosing overheating of a field-effect transistor for diagnosing the problem.

[0002]

2. Description of the Related Art Conventionally, in the device disclosed in Japanese Patent Application Laid-Open No. 8-216683, a DC motor as an electric device is connected to a battery via a motor relay circuit, and the DC motor is locked. A current detecting element for detecting the fact is provided between the DC motor and the motor relay circuit.

[0003]

Some electric devices are driven by turning on / off a field-effect transistor. In the field-effect transistor, a lock current flows when the electric device enters a locked state. In some cases, the semiconductor device may be overheated and destroyed, and it is necessary to monitor the field-effect transistor so as not to be overheated. Then, the above-mentioned Japanese Patent Application Laid-Open No. 8-216683 is disclosed.
It is possible to determine whether or not the field effect transistor is overheated by using a current detection element as disclosed in Japanese Patent Application Publication No. Since the temperature is estimated, it is difficult to say that the diagnosis accuracy is excellent. A field effect transistor having a capacity that allows a diagnosis error must be used, and a more expensive field effect transistor is required. Although it is conceivable to directly detect the temperature of the field effect transistor with a thermal sensor, a thermal sensor is required, which leads to an increase in cost.

The present invention has been made in view of the above circumstances, and has been made in view of the above circumstances, and is an electric device drive circuit capable of reliably and accurately diagnosing the overheating state of a field effect transistor with a simple configuration without increasing the cost. It is an object of the present invention to provide a device for diagnosing overheating of a field-effect transistor.

[0005]

According to a first aspect of the present invention, there is provided an electric equipment driving circuit in which a field effect transistor and an electric equipment are connected in series between a power supply and a ground. Reference voltage setting means for determining a reference voltage corresponding to a preset temperature set in advance based on a lock current flowing through the electric device and a temperature / ON resistance characteristic of the field effect transistor when the electric device locks; Comparison means for comparing a reference voltage set by voltage setting means and a voltage at a connection point between the field-effect transistor and the electric device; and a signal from the comparison means when the voltage at the connection point becomes lower than the reference voltage. Determining means for determining overheating of the field effect transistor based on the output.

According to such a configuration, it is possible to obtain an ON resistance when the temperature of the field-effect transistor reaches an allowable limit based on the temperature-ON resistance characteristics of the field-effect transistor. Since the lock current flowing when the lock state is obtained is also known, based on the ON resistance and the lock current when the temperature of the field effect transistor reaches an allowable limit, the temperature of the field effect transistor can be adjusted to the allowable temperature. It is possible to obtain the amount of voltage drop in the field effect transistor at the time of reaching. In addition, since the ON resistance of the field effect transistor increases as the temperature rises, the voltage drop at the field effect transistor increases as the temperature of the field effect transistor rises, and the voltage at the connection point between the field effect transistor and the electric device is increased. Will be lower. Therefore, a reference voltage for determining the overheating state of the field-effect transistor based on the voltage at the connection point is determined based on the amount of voltage drop in the field-effect transistor when the temperature of the field-effect transistor reaches an allowable limit. It is possible to accurately and reliably diagnose that the field effect transistor is likely to be overheated based on the fact that the voltage at the connection point becomes lower than the reference voltage. Therefore, a current detection element, a heat sensor, and the like are unnecessary, and a large-capacity field-effect transistor that allows a diagnosis error is not required, so that overheat diagnosis of the field-effect transistor can be performed simply and at low cost. .

[0007] The invention according to claim 2 provides the above-described claim 1.
In addition to the configuration of the invention described above, the electric device is a DC motor, and the determination unit determines that the signal indicating that the voltage at the connection point is lower than the reference voltage lasts for a preset time or more. Then, it is determined that the field effect transistor is in an overheated state according to the output from the comparing means.

According to the configuration of the second aspect of the present invention, it is possible to avoid erroneous diagnosis that the field-effect transistor is in an overheated state when the operation of the DC motor that is not in the locked state is started. That is, when the DC motor is normal, an inrush current of the same level as the lock current flows for a certain period of time from the start of the operation of the DC motor, whereas in the locked state of the DC motor, the lock current continues until the drive ends. By determining that the state in which the voltage between the field-effect transistor and the electric device exceeds the reference voltage has continued for a predetermined time or more,
The overheat state of the field effect transistor based on the locked state of the DC motor can be diagnosed reliably.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below based on one embodiment of the present invention shown in the accompanying drawings.

FIGS. 1 to 4 show one embodiment of the present invention. FIG. 1 is a circuit diagram showing a configuration of a drive circuit of a DC motor, FIG. 2 is a temperature / ON resistance characteristic diagram of a field effect transistor, FIG. 3 is a flowchart showing a determination procedure of the determination means,
FIG. 4 is a current waveform diagram showing a normal state and a locked state of the DC motor in comparison.

First, in FIG. 1, a battery 1 as a power supply
Field-Effect Transistor (Field Effe)
ct Transistor (hereinafter referred to as FET) 2 and a DC motor 3 as an electric device are connected in series. The DC motor 3 drives, for example, a pump used in an antilock brake control device in a vehicle brake device.

A motor drive control means 4 is connected to the gate of the FET 2, and the motor drive control means 4
The operation of the DC motor 3 is controlled according to the voltage applied to the gate of the DC motor 2.

The battery 1 is connected to reference voltage setting means 5 for setting a reference voltage. This reference voltage setting means 5
Are divided between the battery 1 and the ground, for example, the voltage dividing resistors 6 and 7
Are connected in series.
Voltage between is output as the reference voltage V _R. The reference voltage V _R obtained by the reference voltage setting means 5 is input to a non-inverting input terminal of a comparator 8 serving as a comparison means. The voltage V at the connection point 9 between the FET 2 and the DC motor 3 is input to the inverting input terminal of the comparator 8.

The FET 2 has a relationship between its temperature and ON resistance as shown in FIG.
The ON resistance R _L (for example, 18) when the temperature of the FET 2 reaches an allowable limit temperature T _L (for example, 150 ° C.).
mΩ) can be obtained based on the temperature / ON resistance characteristics in FIG. On the other hand, since the direct current motor 3 is apparent lock current which flows when the locked state, in accordance with said lock current and ON resistance R _L when reaching the temperature T _L of the limits FET2 is acceptable, FET2 is acceptable It is possible to obtain the voltage drop amount ΔV _L at the FET 2 when the temperature reaches the limit temperature _TL . In addition, since the ON resistance of FET2 increases as the temperature rises as shown in FIG.
As the temperature rises, the voltage drop amount ΔV _L increases, and the voltage V at the connection point 9 between the FET 2 and the DC motor 3 increases.
Will be lower. Thus the voltage of the battery 1 is taken as V _B, if defining a reference voltage V _R for determining that reached a temperature T _L of the limits FET2 is acceptable and (V _B -ΔV _L), wherein the reference voltage V _R the voltage V at the connection point 9
When the temperature is lower than the threshold, it can be determined that the temperature of the FET 2 has exceeded the allowable limit temperature _TL , and the comparator 8 outputs a high-level signal in such a state.

The output signal of the comparator 8 is input to the judging means 10, which judges whether or not the FET 2 has overheated based on the output of the comparator 8, and determines that the FET 2 has overheated. When it is determined that the transistor 11 has been turned on, a signal for turning on the transistor 11 is output. Thus, transistor 11
Is provided between the gate of the FET 2 and the ground. When the transistor 11 is turned on, the FET 2 is cut off regardless of the output of the motor drive control means 4 and the power supply to the DC motor 3 is forcibly stopped. Will do.

The judgment procedure shown in FIG. 3 is set in the judgment means 10 in advance. In step S1, whether the comparator 8 outputs a high-level signal, that is, the voltage V at the connection point 9 is determines whether it is less than the reference voltage V _R output from the reference voltage setting unit 5, when was V <V _R proceeds to step S2, to measure the time in the state is V <V _R.

In step S3, it is determined whether or not the time measured in step S2 has exceeded the set time. If it is determined that the set time has elapsed, F is determined in step S4.
It is determined that ET2 has overheated and the transistor 11
Will be conducted.

That is, the judgment means 10 determines that the voltage V at the connection point 9 between the FET 2 and the DC motor 3 is equal to the reference voltage V _R.
In response to the output of the signal indicating that the current value is less than the preset time from the comparator 8 for a predetermined time or more, F
When it is determined that ET2 is in an overheated state, the transistor 11
And the power supply to the DC motor 3 is forcibly stopped.

Next, the operation of this embodiment will be described. The voltage V at the connection point 9 between the FET 2 and the DC motor 3 is equal to the reference voltage V _R set by the reference voltage setting means 5.
Based on the output of the high level signal from the comparator 8 when the value becomes less than the threshold value, it is determined that the FET 2 is overheated, and the power supply to the DC motor 3 is stopped. Moreover, the reference voltage V _R has reached a limit temperature _TL at which the FET 2 is allowed to be based on the lock current flowing through the DC motor 3 as the DC motor 3 locks and the temperature / ON resistance characteristics of the FET 2. F determined by the resistance R _L
This is set by the reference voltage setting means 5 based on the amount of voltage drop at ET2. Therefore, based on the fact that the voltage V at the connection point 9 becomes lower than the reference voltage V _R, it is possible to accurately and reliably diagnose that the FET 2 is likely to be overheated. FE with a large capacity that makes it unnecessary and allows diagnostic errors
Eliminates the need to use T2, FE is simple and low cost
The overheating diagnosis of T2 can be performed.

The judging means 10 responds to the output of the signal indicating that the voltage V at the connection point 9 is lower than the reference voltage V _R from the comparator 8 continuously for a preset time or more. Thus, it is determined that the FET 2 is in an overheated state. According to the determination by the determination means 10, the FE is erroneously detected when the DC motor 3 is not in the locked state and starts operating.
It is possible to avoid erroneous diagnosis that T2 is in an overheated state.

That is, when the DC motor 3 is normal, as shown by a solid line in FIG. 4, an inrush current of the same level as the lock current flows for a certain time from the start of operation of the DC motor 3, In the locked state of the motor 3, a lock current as shown by a broken line in FIG. By setting the time, it is possible to avoid an erroneous diagnosis due to the inrush current and to reliably diagnose the overheating state of the FET 2 based on the locked state of the DC motor 3.

Although the embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments, and various design changes can be made without departing from the present invention described in the appended claims. It is possible to do.

For example, the present invention is widely applicable not only to a DC motor for driving a pump used in an antilock brake control device but also to electric equipment connected to a power supply via FET2.

[0024]

As described above, according to the first aspect of the present invention, a current detecting element and a heat sensor are not required, and
The need to use a field-effect transistor having a large capacitance that allows a diagnosis error is eliminated, and the possibility that the field-effect transistor is likely to be overheated can be diagnosed simply, at low cost, and accurately.

According to the second aspect of the present invention, it is possible to avoid erroneous diagnosis that the field effect transistor is in an overheated state when starting operation of the DC motor which is not in the locked state.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a drive circuit of a DC motor.

FIG. 2 is a temperature / ON resistance characteristic diagram of a field effect transistor.

FIG. 3 is a flowchart illustrating a determination procedure of a determination unit.

FIG. 4 is a current waveform diagram showing a normal state and a locked state of the DC motor in comparison.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Battery as power supply 2 ... Field effect transistor 3 ... DC motor as electric equipment 5 ... Reference voltage setting means 8 ... Comparator as comparison means 9 ... Connection point 10 ... Determining means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H03K 17/687 H03K 17/687 A (72) Inventor Naoki Obuse 840 Kokubu, Oda, Ueda-shi, Nagano Nissin Kogyo (72) Inventor Yusuke Takayama 1-4-1 Chuo, Wako-shi, Saitama F-term in Honda R & D Co., Ltd. (Reference) 5H430 BB01 BB09 EE06 FF01 FF13 HH03 LA07 LA10 LA11 LA15 LA26 LB02 5H571 AA03 BB07 BB10 CC04 FF06 GG05 HA01 HA08 HA09 HB01 JJ18 LL23 MM06 5J055 AX15 AX53 AX64 BX16 CX20 DX12 DX53 EX07 EX12 EY01 EY17 EY21 EZ00 EZ10 FX12 FX17 FX35 GX01 GX03 GX04 GX06 5J091 AA01 CAA17CA02 GPA11 SA00 TA04 TA06 TA07

Claims (2)

[Claims] An electric device driving circuit in which a field effect transistor (2) and an electric device (3) are connected in series between a power supply (1) and a ground, with the electric device (3) being locked. Current flowing through the electric device (3) and the temperature / O of the field effect transistor (2)
A reference voltage setting means for determining a reference voltage corresponding to a preset temperature based on the N-resistance characteristic; a reference voltage set by the reference voltage setting means; and the field effect transistor. And a comparing means (8) for comparing a voltage at a connection point (9) of the electric device (3), and a signal from the comparison means (8) when the voltage at the connection point (9) becomes lower than the reference voltage. A judging means (10) for judging overheating of the field-effect transistor (2) based on a signal output. 2. The electric device (3) is a DC motor, and the judging means (10) presets a signal indicating that the voltage at the connection point (9) is lower than the reference voltage. 2. The electric device driving circuit according to claim 1, wherein it is determined that the field effect transistor is overheated in accordance with the output from the comparison means for a predetermined time or more. Diagnostic device for field effect transistors in Japan.