JPH01209919A - Motor protecting circuit - Google Patents

Abstract

PURPOSE:To effectively forcibly release a motor from a power source by outputting an alarm signal from a monitor when a surface temperature detected by a thermistor mounted in the motor becomes a predetermined value or more, and supplying a large current to a common fuse. CONSTITUTION:A thermistor 3 having a negative resistance property is mounted on a motor 1, and connected in series with a resistor R3 between a power source voltage Vcc and a ground. A voltage V0 divided by the thermistor 3 and the resistor R3 is input to one of a comparator 41. A reference voltage Vref formed of resistors R4, R5 and a capacitor C from the power source voltage Vcc is input to the other of the comparator 41. When the difference between both the input V0 and the Vref exceeds a predetermined value, the comparator 41 outputs an alarm signal to turn ON a transistor Tr 51, a large current flows from the power source Vbb through a common fuse 2, thereby forcibly melting the fuse 2. Thus, the overheat of the motor 1 is sensitively detected, the motor 1 is forcibly released from the power source to be effectively protected.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a protection circuit that detects abnormal operation of a motor and shuts off the power supply circuit. The common fuse installed between the motor and the power supply, the thermistor attached to the motor to detect the surface temperature, and the output signal level of the thermistor are compared with a preset reference value to determine the output signal level. It consists of a monitoring circuit that outputs an alarm signal when it exceeds a reference value, and a cutoff circuit that causes a large current to flow through the common fuse and force it to open when the alarm signal is output.

[Industrial application field]

The present invention relates to a drive circuit for a small motor incorporated in various electronic devices, and particularly to a protection circuit that detects abnormal operation of a motor and shuts off a power supply circuit.

Input/output devices such as personal computers and word processors have various control circuits and small motors built into extremely narrow spaces, and if an abnormality such as an overload is applied to such a small motor, the motor may The amount of heat generated inside the coil will increase, and in severe cases, the coil will burn out. In addition, not only the motor but also the surrounding control circuits may be thermally destroyed.

As a means to prevent such thermal breakdown, a fuse is generally provided between the motor and the power source, and the fuse is configured to blow when the current increases due to abnormal operation of the motor. However, if the change in current before and after that is small, the fuse may not blow, and the current value when the fuse blows varies widely, so it cannot be said to be perfect.

Therefore, in devices where prevention of thermal damage due to abnormal motor operation is important, it is important to have a protection circuit that can detect an increase in heat generation due to abnormal motor operation at an early stage and can reliably shut off the power supply circuit. required.

[Prior art and problems to be solved by the invention] FIG. 4 is a circuit diagram showing a conventional protection circuit.

In the figure, a motor 1 driven by direct current has a coil 11 connected to a power source Vbb via external resistors R1 and R2 in order to obtain a desired rotation speed. A common fuse 2 is provided between the external resistors R1 and R2 and the power supply Vbb as a means to prevent the motor 1 from burning out when an abnormality such as overload occurs.

However, if the coil and external resistor are connected in series as shown in the figure, even if the current flowing through the coil increases due to abnormal operation, the difference from normal operation is small, and such a change in current value will not blow the common fuse. There are cases. Furthermore, there is a large variation in the current value when a fuse blows, and if a fuse with a small margin is selected so that it will blow due to a slight fluctuation in the current value that occurs during abnormal operation, there is a problem that the common fuse will often blow even during normal operation. .

[Means to solve the problem]

FIG. 1 is a circuit diagram showing a protection circuit according to the present invention, and the same objects are represented by the same symbols throughout the figures.

The above problem was solved by comparing the common fuse 2 provided between the motor 1 and the power supply Vbb, the thermistor 3 attached to the motor 1 to detect the surface temperature, and the output signal level of the thermistor 3 with a preset reference value. A monitoring circuit 4 that outputs an alarm signal when the output signal level exceeds a reference value.
This problem is solved by the motor protection circuit of the present invention, which is comprised of a cutoff circuit 5 that causes a large electric current to flow through the common fuse 2 and forcibly opens it when an alarm signal is output.

[Effect]

In Figure 1, by constantly monitoring the surface temperature of the motor using a thermistor and a monitoring circuit, for example, even if the change in current value is small when an abnormality occurs in the motor, an increase in heat generation due to abnormal operation of the motor can be prevented. This enables early detection, and even if there is a large variation in the current value when a fuse blows, if abnormal motor operation is detected, a large current is applied to the common fuse via the cutoff circuit to force it to open. The power supply circuit can be reliably cut off by this.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to FIG. Note that FIG. 2 is a diagram showing an example of the characteristics of the thermistor, and FIG. 3 is a timing chart explaining the operation of the protection circuit.

In Fig. 1, the difference between the protection circuit of the present invention and the conventional protection circuit is that there is a circuit that detects abnormal operation of the motor by monitoring the surface temperature of the motor, and a circuit that forcibly closes the common fuse when an abnormality occurs. The reason is that it is equipped with a circuit that allows it to be opened.

That is, as shown in Fig. 2, a thermistor 3 whose resistance value increases as the temperature decreases and decreases as the temperature increases is attached to the surface of the motor l, and this is connected to the resistor R.
3 in series to divide the power supply voltage Vcc, a change in the resistance value of the thermistor, in other words a change in the surface temperature of the motor 1, can be extracted as a change in the voltage Vo.

The monitoring circuit 4 that detects abnormal operation of the motor is a comparison circuit 41
and a reference voltage generation circuit 42, the reference voltage generation circuit 4
2 is formed by voltage dividing resistors R4 and R5 and a stabilizing capacitor C. The output signal Vo of the thermistor 3 and the reference voltage Vref output from the reference voltage generation circuit 42 are input to the input terminal of the comparator circuit 41, and when the output signal Vo of the thermistor 3 exceeds the reference voltage Vref, The output side of the comparison circuit 41 is configured to be inverted to a high level.

In addition, when an abnormality occurs, an alarm signal input from the monitoring circuit 4 causes a large current to flow through the common fuse to forcibly open it. Resistor R6 is connected to power supply Vbb via common fuse 2.

The operation of the protection circuit will be explained below with reference to the timing chart of FIG.

For example, when an abnormality occurs in the motor, the surface temperature rises as shown in Figure 3 (■), the resistance value of the thermistor decreases as shown in Figure 3 (■), and the output signal Vo of the thermistor becomes as shown in Figure 3 (■).
It increases as shown in . And the thermistor output signal Vo
When the voltage exceeds the reference voltage Vref, the output side of the comparison circuit provided in the monitoring circuit is inverted to a high level as shown in Fig. As shown in Figure 3 (■), a large current flows through the common fuse, forcing it to open.

By constantly monitoring the surface temperature of the motor using the thermistor and monitoring circuit, for example, even if the change in current value is small when an abnormality occurs in the motor, it is possible to quickly prevent an increase in heat generation due to abnormal motor operation. Furthermore, even if there is a large variation in the current value when a fuse blows, if abnormal operation of the motor is detected, a large current will flow through the common fuse via the cutoff circuit to force it to open. This allows the power supply circuit to be shut off reliably.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a protection circuit that can detect a slight difference in surface temperature and reliably shut off the power supply circuit in the event of abnormal operation.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a protection circuit according to the present invention, Fig. 2 is a diagram showing an example of the characteristics of a thermistor, Fig. 3 is a timing chart explaining the operation of the protection circuit, and Fig. 4 is a diagram showing a conventional protection circuit. FIG. In the figure, l is the motor, 2 is the common fuse, 3 is the thermistor, 4 is the monitoring circuit, 5 is the cutoff circuit,
41 represents a comparison circuit, 42 represents a reference voltage generation circuit, and 51 represents a transistor.

Claims (1)

[Claims] A common fuse (2) provided between the motor (1) and the power supply Vbb, a thermistor (3) attached to the motor (1) to detect the surface temperature, and an output signal level of the thermistor (3) set in advance. A monitoring circuit (4) that outputs an alarm signal when the output signal level exceeds the reference value, and when the alarm signal is output, sends a large current to the common fuse (2). A motor protection circuit comprising a cutoff circuit (5) that is forced to open.