JPH07245375A - Load drive device - Google Patents

Abstract

PURPOSE:To provide a load drive device which can easily sense overheating of a switching means like a power transistor. CONSTITUTION:A load driving device comprises a power MOSFET 1 for motor current control, a PCT thermistor 2 whose resistance value increase when temperature rises, resistors 3, 4, a capacitor 5 for preventing oscillation, an ALM board 9, and heat dissipating fins 10. The PCT thermistor 2 can quickly detect heat generation of the power MOSFET 1 by the effect of the ALM board excellent in thermal conductivity. Thereby thermal protection is enabled more quickly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for driving a load such as a motor, and more particularly to overheat protection for the control device.

[0002]

2. Description of the Related Art Conventionally, as a load driving device for a blower motor of a vehicle or the like, there is a driving device including a control device (controller) and a power transistor as a switch means for supplying a current to the blower motor in response to a signal from the controller. Also, as a mechanism to prevent the control device, motor, etc. from being damaged or burned out in the event of an abnormal situation such as motor lock, temperature sensing means consisting of a thermal fuse or thermistor is inserted in the base or collector line of the power transistor, for example. There is something to do. These detect the temperature of the power transistor when it overheats abnormally, and in the temperature fuse, it melts to prevent current from flowing in the power transistor, and in the thermistor, the resistance value changes and The controller monitors the current so that no more current will flow through the power transistor.

The power transistor and the thermal fuse or thermistor are arranged close to each other on the printed circuit board so that overheating of the power transistor can be detected. In order to better detect the overheating of the power transistor, it is necessary to further bring the power transistor and the thermal fuse or thermistor close to each other.

[0004]

However, even if the above-mentioned elements are brought close to each other, there is a limit in the process, and it is not possible to bring them closer to each other. Therefore, the temperature of the power transistor cannot be sensed with higher accuracy. That is, there is a problem that the temperature sensing means has poor thermal response. Therefore, in the above-mentioned conventional technology, it cannot be said that the temperature of the power transistor is actually sufficiently sensed, and it can be said that the control device, the motor, and the like due to overheating of the power transistor can be sufficiently prevented from being damaged or burned. Absent.

Therefore, in view of the above problems, it is an object of the present invention to provide a load driving device which can easily detect overheating of switch means such as a power transistor.

[0006]

Therefore, the inventors of the present application have focused on a substrate on which elements such as power transistors are mounted. This substrate is required to be insulating. That is, the load driving device according to the present invention is connected to a load,
A switch means formed of a semiconductor element for controlling a current flowing through the load, a temperature sensing means for sensing heat generation of the switch means, a board on which the switch means and the temperature sensing means are mounted, and a board mounted on the board. A load driving device having a heat radiation fin, wherein the substrate is an ALN substrate.

The temperature sensing means may be a thermistor. Further, the heat radiation fins may be corrugated fins.

[0008]

According to the load driving device of the present invention, the switch means composed of the semiconductor element and the temperature sensing means for sensing the heat generation of the switch means have good thermal conductivity.
Since it is mounted on the N substrate, the temperature sensing means is
The heat generation status of the switch means can be detected through the ALN substrate.

[0009] With this, it is possible to quickly detect the heat generation state of the switch means, and it is possible to more quickly protect the temperature of the load drive device. That is, there is an excellent effect that the thermal response is improved and the temperature protection of the load driving device can be surely performed. If the temperature sensing means is a thermistor, it can be mounted at the same time as the switch means using the surface mounting technique, so that both can be arranged close to each other, and the thermal response is further improved. Therefore, the temperature of the switch means can be sensed more reliably.

If the heat radiation fin is a corrugated fin, the heat radiation is good and the fin can be made small. As a result, the heat capacity can be reduced, so that the temperature sensing means can sensitively sense the temperature change, and the thermal response is further improved. Therefore, the temperature of the switch means can be sensed more reliably.

[0011]

EXAMPLE An example in which the present invention is applied to a drive device for an automobile air-conditioning blower motor will be described below. FIG. 1A is a plan view of a mounting view showing the blower motor driving device of this embodiment, and FIG. 1B is a sectional view. FIG. 2 is a circuit diagram of the blower motor driving device. The same elements are designated by the same reference numerals in the circuit diagram and the mounting diagram.

In FIG. 1, 1 is a power MOSFET (switch means) for controlling a motor current, 2 is a PTC thermistor (temperature sensing means) whose resistance value increases as temperature rises, 3 and 4 are resistors, and 5 is an oscillation. It is a prevention capacitor. Further, 9 is an aluminum nitride substrate (hereinafter referred to as A
LN substrate) on which power MOSFET
1, PTC thermistor 2, resistors 3 and 4, and capacitor 5 are surface-mounted and soldered on the same surface.

These elements are connected from the terminals on the substrate to the terminals in the case 11 by wire bonding or the like and are connected to the connector. The back surface of the ALN substrate 9 is fixed to the heat radiation fin 10 through grease having high thermal conductivity. The radiating fins are corrugated fins, which have excellent heat radiation properties against forced air cooling.

As described above, in this embodiment, since the power MOSFET 1 and the PTC thermistor 2 are mounted on the ALN substrate 9 having a high thermal conductivity, the thermal coupling between the PTC thermistor 2 and the power MOSFET 1 is sufficient. Can be obtained. Therefore, PTC thermistor 2
Since the temperature of the power MOSFET 1 can be immediately sensed via the LN substrate 9, temperature protection can be applied more quickly. That is, in the blower motor drive device of the present embodiment, the thermal responsiveness to overheating of the power MOSFET 1 is improved, and it is possible to reliably prevent damage or burning of the power MOSFET 1 or the air conditioner ECU 7.

Although the PTC thermistor is used as the temperature sensing means in the above embodiment, a temperature fuse may be used. In that case, when the control device of the power MOSFET 1 abnormally overheats, the thermal fuse is blown to function as overheat protection. However, in the case of using the thermal fuse, it is necessary to take precautions such as using a lead structure and separating the mounting process from other elements so as not to blow when mounting on the substrate.

Next, the operation of the blower motor driving device shown in FIG. 2 will be described. In FIG. 2, 6 is a blower motor, and 7
Is an air conditioner ECU (Electric Control Unit), and 8 is a relay upstream of the motor. Further, the element in the area surrounded by the larger one-dot chain line in FIG.
It is mounted on the N substrate 9. In normal operation, in response to a signal (voltage) from the air conditioner ECU, a voltage corresponding to the divided voltage of the thermistor 2 and the resistor 3 is applied to the gate of the power MOSFET 1, and the voltage between the drain and the source at the operating point based on the voltage. To control the energizing current of the blower motor.

If an abnormal situation such as a motor lock occurs and the air supply is stopped and the control device such as the power MOSFET 1 overheats abnormally, the resistance value of the thermistor 2 increases, so that the voltage applied to the gate of the power MOSFET 1 increases. Along with the decrease, the potential at point A in FIG. 2 rises. Then, this potential is fed back to the air conditioner ECU 7, and since the actual potential is higher than the potential to be controlled, the air conditioner ECU 7 works to raise the gate potential of the power MOSFET 1 in order to lower the potential at the point A. However, the heat generated in the power MOSFET 1 causes the resistance value of the thermistor 2 to increase, so that the power MOSFET 1 is turned off. As a result, the current flowing through the power MOSFET 1 decreases, so that the power consumed by the power MOSFET 1 decreases and the heat generation is suppressed, and the increase in the resistance value of the thermistor is suppressed. As a result, the control is performed in a state in which the gate potential decrease due to heat generation of the control device and the gate potential increase due to heat generation suppression due to the reduction of energization current are balanced, so that the control device such as the power MOSFET 1 and the motor are burnt out. It is possible to protect without doing.

Further, in this state, the air conditioner ECU
Since 7 can monitor the potential at the point A, it senses that the voltage to be controlled does not match, and turns off the relay upstream of the motor or controls the gate to the power MOSFET 1. Further overheat protection can be provided by controlling the output to be completely turned off.

Further, in the case of this configuration, unlike the temperature fuse, the air conditioner ECU 7 detects not only the determination of whether the abnormal state of heat generation is "1" or "0" whether the fuse is blown or not blown, but also the change condition. Therefore, it can be applied to the diagnostic function. Also, as shown in FIG.
Unlike thermal fuses, thermistors do not blow at the soldering temperature, so structurally it is possible to simultaneously surface mount solder on a substrate together with heating elements such as power MOSFETs and other elements. Both the top and the structure can be simplified. Furthermore, power MOSFE
Since it can be mounted by surface mounting at the same time as the heating element such as T, the thermistor can be mounted in the vicinity of the heating element.

Although the present description has been made with the PTC thermistor, the case where the NTC thermistor is used can be constructed by exchanging the positions of the thermistor and the resistor 3. When any of the thermistors is used, if the abnormal situation is resolved and the heat generation returns to the same state as in normal operation, the resistance value of the thermistor returns to its original value, and the function of the control device like a thermal fuse is impaired. It is possible to solve the problem that the device itself has to be replaced with another one.

Further, the radiation fins attached to the ALN substrate can be made extremely small by changing from a large die made of aluminum die casting to a corrugated fin excellent in heat radiation against forced air cooling. Since it is thin, it has a small heat capacity and can improve the thermal response of the thermistor as compared to a large fin made of aluminum die casting.

The attachment position of the blower motor drive device shown in FIG. 1 is a ventilation path (not shown) such as in the blower / scroll or in the cooling unit. According to this embodiment, since the size can be reduced, the air resistance is reduced and the wind noise is prevented. Further, since the size of the blower motor can be reduced, the blower motor itself can be mounted in the return bypass path for cooling, and further reduction of air resistance and prevention of wind noise can be realized.

[Brief description of drawings]

FIG. 1A is a mounting plan view of a motor drive device according to an embodiment. (B) is sectional drawing of (a) figure.

FIG. 2 is a circuit diagram of the motor drive device shown in FIG.

[Explanation of symbols]

 1 Power MOSFET 2 PTC thermistor 3, 4 Resistor 5 Capacitor 9 ALN substrate 10 Radiating fin

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideo Watanabe 1-1-1, Showa-cho, Kariya city, Aichi prefecture Nihon Denso Co., Ltd.

Claims (3)

[Claims] 1. A switch means comprising a semiconductor element connected to a load and controlling a current flowing through the load, a temperature sensing means for sensing heat generation of the switch means, and the switch means and the temperature sensing means are mounted. A load driving device having a substrate and a heat radiation fin installed on the substrate, wherein the substrate is an ALN substrate. 2. The load driving device according to claim 1, wherein the temperature sensing means is a thermistor. 3. The load driving device according to claim 1, wherein the heat radiation fin is a corrugated fin.