JP2010140157A - Protection device for transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten power supply interruption time of a transistor due to a protecting operation. <P>SOLUTION: When the engagement of any foreign matter occurs in a motor 2, the currents of MOSFET 7 and 8 are rapidly increased, and a detection temperature by a diode 15 arranged in the neighborhood of MOSFET7 and 8 is rapidly increased. When the detected temperature exceeds a first overheat protection level T1, a first overheat detection signal S1 is changed to an H level, and the reset state of a latch 27 is released. Afterwards, when detection currents exceed an overcurrent protection level ia, the output signal S3 of the latch 27 is changed to an H level, and the signal S3 in the H level is output only in a fixed power supply interruption time Tm from the point of time. When the detection temperature is decreased to a first overheat protection level T1 or less during the power supply interruption time Tm, the first overheat detection signal S1 is changed to an L level, and the latch 27 is reset. In this case, the second overheat detection signal S2 is put in an L level, and a motor driving circuit 1 is restored from the power supply interruption state to a power supply operation state. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a protection device for a transistor against overcurrent and overheating.

  In a configuration in which the energization of the motor is controlled using a transistor, if a motor lock or a short-circuit of the motor winding occurs, the induced voltage of the motor that existed in the energization path is lost. Flowing. Due to this overcurrent, the temperature of the transistor rises rapidly. However, in an IC or the like, there is a delay in heat conduction from the transistor to the temperature detection element, and a filter may be inserted into the temperature detection circuit to prevent noise. For this reason, the transistor may not be sufficiently protected only by the overheat protection circuit.

  Therefore, the conventional protection device is provided with an overcurrent protection circuit in preparation for a case where the heat generation rise gradient is large and protection by overheat detection cannot be performed. The overcurrent detection circuit stops energization of the transistor as soon as it detects that the current exceeds the overcurrent protection level, and then returns after a certain energization cut-off time has elapsed. In such a protection device, it is possible to protect the IC (transistor) even under worst conditions such as when the ambient environment temperature of the IC is the upper limit value of the allowable operating environment temperature or when the current is the maximum value of the allowable current. In addition, the constant energization cut-off time is set with a margin.

For example, when the overcurrent protection device described in Patent Document 1 detects an overcurrent during preheating of the motor, the preheating operation is temporarily stopped after the preheating operation is temporarily stopped, and the preheating control is performed when the number of retries reaches a predetermined number during preheating. Exit. In addition, the passive belt control device described in Patent Document 2 executes retry control in which when the motor that drives the seat belt is locked, the motor is temporarily stopped, and a drive signal is re-output to the motor after a predetermined time has elapsed. When the number of re-outputs due to the retry reaches a predetermined number, the re-output operation is prohibited.
JP 09-271135 A No. 06-013015

  In the case of a device that drives a motor, even if an overcurrent temporarily flows due to the biting of foreign matter, the foreign matter may be immediately removed due to inertial rotation of the motor, and the motor may return to a normal driving state. However, once the overcurrent is detected, the conventional protection device described above continues to stop the motor drive until a certain energization cut-off time elapses even if the state returns to the state where the rotational drive state can be restored. For this reason, for example, when the fuel pump of the vehicle is driven by a motor, there is a possibility of affecting the rotation of the engine despite the occurrence of a temporary overcurrent.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a transistor protection device capable of shortening the energization cutoff time of the transistor by the protection operation.

  According to the first aspect of the present invention, the current flowing through the transistor is detected, and an overcurrent detection signal is output when the detected current exceeds the overcurrent protection level. In addition, a temperature detecting means is arranged in the vicinity of the transistor, and a first overheat detection signal is output when the detected temperature exceeds the first overheat protection level. The energization control circuit sets the transistor in the energization cut-off state for a certain time from the time when the overcurrent detection signal is output, and the first temperature from the state in which the detected temperature exceeds the first overheat protection level within the certain time. When the output of the first overheat detection signal is stopped at a level below the overheat protection level, the transistor is returned to the energized operation state from the stop point.

  For example, when the ambient temperature of the transistor is the upper limit value of the allowable operating environment temperature, the first overheat protection level is the same as when the current flowing through the transistor during the energization operation is the maximum value of the allowable current. Even in the most severe conditions, the temperature level is set so that the transistor does not fail when the transistor is returned from the energization cutoff state to the energization operation state.

  As a result, when an overcurrent flows through the transistor, the transistor temporarily shifts to the energization cut-off state and the detected temperature exceeds the first overheat protection level. Since the transistor returns to the energized operation state without waiting for the time, the substantial energization interruption time at the time of detecting the overcurrent can be shortened as much as possible. In addition, since the first overheat protection level is set as described above, even if the cause of the overcurrent is still present at the time of returning to the energized operation state, the transistor is not activated until the overcurrent is shut off again. It is possible to prevent failure.

  According to the second aspect of the present invention, the second overheat protection level that is higher than the first overheat protection level and has a high probability of causing a failure in a short time when the transistor is energized is set. When the detected temperature exceeds the second overheat protection level, the transistor is forcibly controlled to be turned off regardless of the output state of the overcurrent detection signal and the first overheat detection signal. Can be protected.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an IC including a motor drive circuit for a vehicle fuel pump. The configuration other than the motor drive circuit and the power supply terminal are omitted. The motor drive circuit 1 built in the IC drives the motor 2 in accordance with an energization command signal Sd for commanding power interruption and has a protection function for protecting the motor 2 from overcurrent and overheating. The motor 2 is connected between the output terminals 3 and 4 of the IC.

  N-channel MOSFETs 7 and 8 (transistors) are connected between the power supply line 5 for supplying the battery voltage VB and the output terminal 3, and between the output terminal 4 and the power supply line (ground line) 6, respectively. Attached to the MOSFET 7 is a MOSFET 9 (current detection means) in which the MOSFET 7 is connected to the gate and the drain. A current 1 / N (N is a constant larger than 1) of the current flowing through the MOSFET 7 flows through the current sensing MOSFET 9.

  A transistor 10 and a resistor 11 are connected in series between the source of the MOSFET 9 and the power supply line 6. The operational amplifier 12 inputs the potentials of the sources of the MOSFET 7 and the MOSFET 9 and drives the base of the transistor 10 by the output voltage. As a result, the drain-source voltages of the MOSFET 7 and the MOSFET 9 are controlled to be equal, and the current flowing through the MOSFET 7 can be detected more accurately. The protection current setting circuit 13 generates a reference voltage Va corresponding to the overcurrent protection level ia for the MOSFET 7. The comparator 14 (current comparison circuit) compares the voltage across the resistor 11 with the reference voltage Va, so that when the current (detection current) flowing through the MOSFET 7 exceeds the overcurrent protection level ia, the H level overcurrent. The detection signal Sa is output.

  In the IC, a diode 15 (temperature detecting means) is formed in the vicinity of the MOSFETs 7 and 8. In order to improve the temperature detection accuracy, the constant current circuit 16 supplies a constant current to the diode 15 from the power supply line 17 that supplies the control power supply voltage Vcc. The first protection temperature setting circuit 18 sets a reference voltage V1 corresponding to the first overheat protection level T1 for the MOSFETs 7 and 8, and is composed of a series circuit of resistors 19 and 20. The comparator 21 (first temperature comparison circuit) compares the forward voltage Vf of the diode 15 with the reference voltage V1, so that when the detected temperature exceeds the first overheat protection level T1, 1 overheat detection signal S1 is output. As is well known, the forward voltage Vf of the diode has a temperature coefficient of about -2 mV / ° C.

  On the other hand, the second protection temperature setting circuit 22 sets a reference voltage V2 corresponding to the second overheat protection level T2 for the MOSFETs 7 and 8, and is composed of a series circuit of resistors 23 and 24. The comparator 25 (second temperature comparison circuit) compares the forward voltage Vf of the diode 15 with the reference voltage V2, so that the H level first voltage is detected when the detected temperature exceeds the second overheat protection level T2. 2 overheat detection signal S2 is output.

  The first overheat detection signal S1 and the power-on reset signal POR are input to the AND gate 26, and the output signal of the AND gate 26 is input to the reset terminal of the latch 27. The power-on reset signal POR becomes L level for a predetermined time after power is supplied to the IC. While the output signal of the AND gate 26 is at the L level, the latch 27 is in the reset state, and the output signal of the latch 27 is at the L level. When the overcurrent detection signal Sa input to the clock terminal changes from the L level to the H level, the latch 27 (energization control circuit) outputs an H level signal S3 for a certain energization cutoff time Tm from that point.

  The output signal S3 of the latch 27 and the overheat detection signal S2 are given to the AND gate 29 via the NOR gate 28. The AND gate 29 also receives the energization command signal Sd, and the output signal drives the gates of the MOSFETs 7 and 8 through the buffer circuit 30. As a result, when an H level signal is input from the AND gate 29, the buffer circuit 30 drives the MOSFETs 7 and 8 on, and when an L level signal is input, the buffer circuits 30 drives the MOSFETs 7 and 8 off. Of the motor drive circuit 1 described above, the circuit excluding the MOSFETs 7 and 8 and the buffer circuit 30 corresponds to the transistor protection device in the present invention.

Next, operations and effects of the present embodiment will be described with reference to FIG.
First, each protection level used in the motor drive circuit 1 will be described. The overcurrent protection level ia is set under worst conditions, such as when the ambient temperature of the IC (for example, the internal temperature of the on-vehicle electronic control device on which the IC is mounted) is the upper limit of the environmental temperature allowed for operation. This is the maximum rated current of the MOSFETs 7 and 8. When a current exceeding the overcurrent protection level ia flows through the MOSFETs 7 and 8, the channel temperature rises rapidly, resulting in a failure due to the overcurrent in a short time.

  The first overheat protection level T1 is the maximum allowable current (the above-described maximum rating) when the ambient temperature of the IC is the upper limit of the environmental temperature allowed for operation or when the current flows through the MOSFETs 7 and 8 during energization operation. Even when the MOSFETs 7 and 8 are thermally severely conditioned as in the case where the current is smaller than the current), the MOSFETs 7 and 8 are restored when the MOSFETs 7 and 8 are returned from the energization cut-off state to the energization operation state. 8 is set to a temperature level at which no failure occurs. The second overheat protection level T2 is a temperature level higher than the first overheat protection level T1, and if the MOSFETs 7 and 8 are energized when the detected temperature exceeds the level T2, the second overheat protection level T2 breaks down in a short time. Temperature.

  FIG. 2 shows a waveform of each part when an overcurrent that temporarily exceeds the overcurrent protection level ia flows due to a foreign object being caught, a wiring short circuit, a winding short circuit, or the like while the motor 2 is being driven. The waveforms of the current (detection current) of the MOSFET 7, the overcurrent detection signal Sa, the output signal S3 of the latch 27, the forward voltage Vf of the diode 15, and the first overheat detection signal S1 are shown in order from the top.

  In a normal driving state before time t1, since the detected current is smaller than the overcurrent protection level ia, the overcurrent detection signal Sa remains at the L level. Since the detected temperature is also lower than the first overheat protection levels T1 and T2, the first and second overheat detection signals S1 and S2 output from the comparators 21 and 25 are also at the L level. As a result, the output signal S3 of the latch 27 becomes L level, and the buffer circuit 30 drives the MOSFETs 7 and 8 on and off in accordance with the energization command signal Sd.

  When a foreign object bite, a wiring short circuit, a winding short circuit, etc. occur at time t1, the currents of the MOSFETs 7 and 8 increase rapidly, and the channel temperature of the MOSFETs 7 and 8 and thus the detected temperature increase rapidly. When the detected temperature exceeds the first overheat protection level T1 at time t2 (that is, when the forward voltage Vf of the diode 15 falls below the reference voltage V1), the first overheat detection signal S1 changes from the L level to the H level. Then, the reset state of the latch 27 is released.

  Thereafter, when the detected current exceeds the overcurrent protection level ia at time t3, the overcurrent detection signal Sa changes to H level, and the output signal S3 of the latch 27 changes from L level to H level. The constant H level period (energization cut-off time Tm) set at this time is the maximum allowable current when the ambient temperature of the IC is the upper limit of the environmental temperature allowed for operation or when the current flowing through the MOSFETs 7 and 8 is the maximum allowable current. This is a time during which energization can be started with a sufficient temperature margin at the time of energization return (time t5) even under severely thermal conditions such as a value. In the prior art, the energization is always restored after waiting for the energization cut-off time Tm.

  When the overcurrent is detected, the energization is stopped and the detected temperature gradually decreases. When the detected temperature falls below the first overheat protection level T1 (that is, when the forward voltage Vf of the diode 15 becomes higher than the reference voltage V1), the first overheat detection signal S1 changes from the H level to the L level, The latch 27 is reset. At this time, since the second overheat detection signal S2 is also at the L level, the motor drive circuit 1 returns from the energization cut-off state to the energization operation state.

  When the detected temperature exceeds the second overheat protection level T2 (that is, when the forward voltage Vf of the diode 15 is lower than the reference voltage V2), the second overheat detection signal S2 becomes H level and the overcurrent Regardless of the output state of the detection signal Sa and the first overheat detection signal S1, the power supply is immediately cut off.

  Further, when the detected temperature does not exceed the first overheat protection level T1, the output signal S3 of the latch 27 is held at the L level. In this case, since the latch 27 remains in the reset state, energization is continued unless the detected temperature subsequently falls below the second overheat protection level T2.

  On the other hand, when the forward voltage Vf of the diode 15 falls below the reference voltage V1 after the overcurrent detection signal Sa changes to the H level, the energization cannot be cut off based on the overcurrent detection signal Sa. When such a situation may occur due to the configuration of the IC, the latch 27 is configured so that the signal S3 becomes the H level when the first overheat detection signal S1 changes to the H level regardless of the state of the reset signal. do it.

  As described above, the motor drive circuit 1 according to the present embodiment detects the current flowing through the MOSFET 7 and outputs the H level overcurrent detection signal Sa when the detected current exceeds the overcurrent protection level ia. Is temporarily stopped. After that, while waiting for the passage of a certain energization cut-off time Tm, when the detected temperature becomes lower than T1 from the state where the first overheat protection level T1 exceeds the first overheat protection level T1, the first overheat detection signal S1 returns to the L level. Without waiting for the energization interruption time Tm to elapse, the apparatus immediately returns to the energization operation state from that point.

  Even if the MOSFETs 7 and 8 are returned to the energized operation state while the abnormal state such as foreign matter biting, wiring short-circuiting, winding short-circuiting or the like continues while the first overheat protection level T1 The temperature is set so that the MOSFETs 7 and 8 do not fail during the energization period. Therefore, it is possible to return to the driving operation state of the motor 2 in a short time without waiting for the energization interruption time Tm to elapse while protecting the MOSFETs 7 and 8 from overcurrent and overheating.

  Further, since the inherent on-resistance Ron and static characteristics of the MOSFETs 7 and 8 vary from IC to IC, the heat generation characteristics (temperature rise characteristics) due to energization of the MOSFETs 7 and 8 also vary. Therefore, in the conventional configuration in which the energization is interrupted uniformly only during the energization interruption time Tm when an overcurrent is detected, it is necessary to determine the energization interruption time Tm on the basis of the element with the largest amount of heat generation in consideration of product variations. It was easy to cut off time.

  On the other hand, in the present embodiment, the temperature is continuously detected even after the overcurrent is detected, and the power supply is restored on condition that the temperature is lower than the first overheat protection level T1, thereby eliminating the influence of the above-described variation of elements and the like. Thus, reliable protection and shortening of the shut-off period can be realized. Note that since the forward voltage Vf of the diode 15 also varies, it is preferable to employ a temperature detecting means with little variation instead of the diode 15.

  The motor 2 of the present embodiment drives a fuel pump that supplies fuel to the injector. In the electronically controlled fuel injection device, when the energization of the motor 2 is interrupted and the rotational speed is reduced, the fuel pressure applied to the injector is lowered and the engine is eventually stopped. Further, when the motor 2 is a sensorlessly driven brushless motor, it takes a start-up time to start the motor 2 that has been stopped. The motor drive circuit 1 according to the present embodiment returns the motor 2 to the energized state at an earlier timing than before when an overcurrent is detected, so that the motor drive circuit 1 can be recovered from the inertial rotation state with little reduction in the rotation speed. It is possible to prevent the engine from being stopped.

The present invention is not limited to the embodiment described above and shown in the drawings. For example, the present invention can be modified or expanded as follows.
When processing using a microcomputer or a logic circuit, digital values of the reference voltages V1 and V2 corresponding to the first and second overheat protection levels T1 and T2 are stored in advance in a memory (corresponding to the first and second protection temperature setting circuits). ), The forward voltage of the diode 15 may be A / D converted, and the processor (CPU) may execute the first and second temperature comparison processing and the energization control processing. Further, the digital value of the reference voltage Va corresponding to the overcurrent protection level ia may be written in the memory in advance, the voltage across the resistor 11 is A / D converted, and the current comparison process and the energization control process may be executed by the processor. In these cases, the constant energization cut-off time Tm may be set using a timer.

  The motor 2 is not limited to a drive motor for a vehicle fuel pump, and can be widely applied to a motor that is required to prevent the rotation from being stopped or the rotation speed from being lowered, such as a motor used in an electric vehicle or an elevator.

The block diagram of the motor drive circuit which shows one Embodiment of this invention Waveform diagram of each part when overcurrent flows temporarily

Explanation of symbols

  In the drawing, 7 and 8 are MOSFETs (transistors), 9 is a MOSFET (current detection means), 13 is a protection current setting circuit, 14 is a comparator (current comparison circuit), 15 is a diode (temperature detection means), and 18 is a first. Protection temperature setting circuit, 21 is a comparator (first temperature comparison circuit), 22 is a second protection temperature setting circuit, 25 is a comparator (second temperature comparison circuit), and 27 is a latch (energization control circuit). .

Claims (2)

Current detection means for detecting a current flowing through the transistor;
A protection current setting circuit for setting an overcurrent protection level for the transistor;
A current comparison circuit that outputs an overcurrent detection signal when the detection current exceeds the overcurrent protection level;
Temperature detecting means disposed in the vicinity of the transistor;
A first protection temperature setting circuit for setting a first overheat protection level for the transistor;
A first temperature comparison circuit that outputs a first overheat detection signal when the detected temperature exceeds the first overheat protection level;
The transistor is set in the energization cut-off state for a predetermined time from the time when the overcurrent detection signal is output from the current comparison circuit, and the first temperature comparison circuit within the predetermined time causes the first temperature comparison circuit to perform the first overheat detection signal. And a current-carrying control circuit for returning the transistor to a current-carrying operation state when the output is stopped. A second protection temperature setting circuit for setting a second overheat protection level at a temperature higher than the first overheat protection level;
A second temperature comparison circuit that outputs a second overheat detection signal when the detected temperature exceeds the second overheat protection level;
When the second temperature comparison circuit outputs the second overheat detection signal, the energization control circuit controls the transistor regardless of the output state of the overcurrent detection signal and the first overheat detection signal. 2. The transistor protection device according to claim 1, wherein the transistor is forcibly controlled to be in a power-off state.

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