JPH05227784A - Motor drive circuit - Google Patents

Abstract

PURPOSE:To suppress temperature rise of coil by connecting a thermister with the base of a transistor for controlling the current flowing into a motor drive coil and feeding the base current of the transistor to the ground upon temperature rise of the coil thereby reducing the current flowing through the transistor. CONSTITUTION:A Hall element HIC magnetically detects the position of a rotor and if thus detected signal has high level, a transistor Q1 is turned ON to feed a current to a motor driving coil L1 and when the signal level goes Low, the transistor Q1 is turned OFF while a transistor Q2 is turned ON to feed a current to a motor driving coil L2 thus imparting a rotating force to a roller. If the temperature rises due to some cause, resistance of a thermister TH decreases and the current to be fed to the bases of the transistors Q1, Q2 flow through a diode D1 or D2 and a thermister TH to the ground and thereby the collector current decreases. Consequently, currents flowing through the motor drive coils L1, L2 decrease to suppress heating.

Description

Detailed Description of the Invention

The present invention relates to a motor drive circuit used for a cooling fan of a personal computer or a word processor, and more particularly to a motor drive circuit capable of preventing overheating of a motor drive coil.

[0002]

2. Description of the Related Art In recent years, devices such as personal computers have been widely used. However, many of these devices are provided with a cooling fan so that the inside of the device does not overheat.

There is a system called impedance protection as one system of a motor drive circuit for driving the fan, which is constructed as shown in FIG. 3, for example. This is an example of a two-phase motor, and the motor drive coil L ₁ ,
The rotor is rotated by passing a current through L ₂ . Specifically, the Hall IC (HIC) magnetically detects the position of the rotor and operates the transistor Q ₁ to control the current flowing through the coil L ₁ . And wherein connected to the collector of the transistor Q ₁ to the base of the transistor Q _2, in which the on-transistors Q _1, by operating the transistor Q ₂ to invert off to control the current flowing through the coil L _2.

This motor drive circuit keeps the current flowing through the coils L ₁ and L ₂ even if the blades of the rotating fan are locked due to some external factor.
It is inexpensive because it does not require a special protection circuit, and is often used in small cooling fans.

[0005]

However, even if the temperature of the coil is increased by continuing to supply the current to the coils L ₁ and L ₂ in the motor drive circuit, the temperature of the motor drive circuit is kept below the allowable temperature of the coil. There must be. For that purpose, it was necessary to sufficiently design the heat.

Further, since a large fan has a large current flowing through the coil and the temperature of the coil rises greatly, there is a possibility that dielectric breakdown may occur if the current continues to flow. Therefore, the motor drive circuit can be applied only to a small fan in which the current flowing through the coil is small.

The object of the present invention is to solve the above-mentioned conventional problems,
(EN) A motor drive circuit capable of preventing overheating due to a coil by reducing a current flowing through the coil when the temperature rises.

[0008]

In order to achieve the above object, the structure according to the present invention controls a current flowing through a motor drive coil in a motor drive circuit which causes a current to flow through the motor drive coil to rotate a rotor. One end of the thermistor is connected to the base of the transistor via a diode, the other end of the thermistor is connected to the ground, and the transistor is connected to the ground via the diode.

[0009]

In the above structure, when the temperature of the coil rises for some reason, the resistance value of the thermistor decreases, and the base current of the transistor starts to flow to the ground, so that the current flowing through the transistor decreases. The current flowing through the drive coil is reduced. Therefore, the temperature rise of the coil is suppressed, and the insulation breakdown of the coil due to overheating is prevented. It can also be used for large fan motors.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the motor drive circuit according to the present invention will be specifically described with reference to FIGS. Incidentally, FIG.
2 is a configuration explanatory view of a motor drive circuit, and FIG. 2 is an operation timing chart.

In FIG. 1, this motor drive circuit shows a drive circuit of a two-phase motor, and motor drive coils L ₁ and L are connected to a power supply terminal t _V which supplies a DC voltage V _CC as an operating voltage.
₂ are connected to each other, and the coils L ₁ and L ₂ are connected to the ground (negative power supply) terminal t ₀ via the transistors Q ₁ and Q ₂ and the diode D ₀ .

The transistors Q ₁ and Q ₂ control the currents flowing in the coils L ₁ and L _2. The base of the transistor Q ₁ magnetically detects the rotation of the rotor and outputs high and low signals. Hall IC (HIC) and resistance R ₁
Are connected, and the base of the transistor Q ₂ is connected to the collector of the transistor Q ₁ via the resistor R ₂ .

Further, the bases of the transistors Q ₁ and Q ₂ are connected to the terminal t ₀ through the diodes D ₁ and D ₂ and the thermistor TH having a negative characteristic with respect to temperature, respectively.

[0014] The transistor Q _1, the collector of Q ₂ - Zener for protecting the transistors Q _1, Q ₂ by clamping the high voltage generated by the counter electromotive force emitter between each of the coil L _1, L ₂ Diode D
_Z1 and D _Z2 are connected.

Next, the operation of the motor drive circuit having the above construction will be described with reference to the timing chart of FIG. First, a normal operation in which the temperature does not increase and the thermistor TH has a high resistance value will be described. Power on and coil L ₁ ,
When a current is supplied to L ₂ and a rotor (not shown) rotates, the Hall IC outputs high and low signals according to the magnetic poles of the rotor. When this signal is at a high level, the base voltage of the transistor Q ₁ becomes high, current is supplied to the base, and the transistor Q ₁ is turned on. Therefore, a current flows through the coil L ₁ , and the electromagnetic force imparts a rotational force to the rotor.

When the transistor Q ₁ is turned on and a current is flowing through the coil L ₁ , the collector voltage of the transistor Q ₁ becomes low level, the base of the transistor Q ₂ also becomes low level, and the transistor Q ₂ is turned off. It becomes a state. Therefore, no current flows through the coil L ₂ .

Next, when the rotor rotates and the output of the Hall IC becomes low level, the base of the transistor Q ₁ becomes low level, so that the transistor Q ₁ is turned off and no current flows through the coil L ₁ . At this time, the transistor Q
_Since the collector voltage of ₁ becomes high level, the base of the transistor Q ₂ also becomes high level and the transistor Q ₂ is turned on. For this reason, a current flows through the coil L ₂ , and the electromagnetic force imparts a rotational force to the rotor.

In the above operation, when the temperature rises and the thermistor TH has a high resistance value, the transistor Q
Sufficient base current is supplied to ₁ and Q ₂ .

The operation when the temperature rises for some reason will now be described. At this time, the resistance value of the thermistor TH decreases. Therefore, even if the output of the Hall IC becomes high level, the current supplied to the base of the transistor Q ₁ flows to the ground through the diode D ₁ and the thermistor TH. Thus, sufficient base current is not supplied to the transistor Q _1, to be reduced collector current of the transistor Q _1, the current flowing through the coil L ₁ decreases.

Similarly, even if the output of the Hall IC becomes low level and the collector voltage of the transistor Q ₁ becomes high level, the current supplied to the base of the transistor Q ₂ flows to the ground through the diode D ₂ and the thermistor TH. I will end up. Therefore, not supplied sufficient base current to the transistor Q _2, since the collector current of the transistor Q ₂ becomes small, and decreases the current flowing through the coil L _2.

When the temperature rises in this way, the thermistor
By reducing the resistance value of TH and flowing the base current of the transistors Q ₁ and Q ₂ to the ground via the thermistor TH, the collector current is reduced and the current flowing through the coils L ₁ and L ₂ is reduced. The control circuit operates. This suppresses heat generation of the coils L ₁ and L ₂ and prevents the coil temperature from rising above the allowable temperature.

Since the emitters of the respective transistors Q ₁ and Q ₂ are connected to the ground terminal t ₀ via the diode D ₀ , the base potentials of the respective transistors Q ₁ and Q ₂ rise, and the thermistor TH is sufficient. Current flows. Therefore, the current supply to the coils L ₁ and L ₂ due to the temperature rise is surely suppressed. If the diode D
_{If 0} is not provided, the voltage applied to the thermistor TH becomes low, so that even if the temperature rises and the resistance value of the thermistor TH decreases, the current flowing through the thermistor TH is small, and therefore the transistors Q ₁ , Q ₂ The base current of is not reduced so much. The diode D ₀ also serves to prevent reverse connection.

When the base currents of the transistors Q ₁ and Q ₂ are released via the thermistor TH as described above, the thermistors are respectively provided to the emitters of the transistors Q ₁ and Q _2.
Although TH may be connected, by connecting each emitter to one thermistor TH via the diodes D ₁ and D ₂ as in the above-described embodiment, the number of thermistors which are more expensive than diodes can be connected. Is preferable because it can be reduced.

Although the two-phase motor drive circuit having two coils has been described in the above embodiment, the present invention can be similarly applied to a motor drive circuit having an increased number of coils.

[0025]

As described above, according to the present invention, when the temperature rises for some reason, the resistance value of the thermistor decreases, the base current of the transistor for controlling the current of the motor drive coil flows to the ground, and the current flowing through the transistor. And the current flowing through the motor drive coil is reduced. Therefore, the temperature rise of the coil is suppressed, and the insulation breakdown of the coil due to overheating is prevented.

[Brief description of drawings]

FIG. 1 is a configuration explanatory diagram of a motor drive circuit according to an embodiment of the present invention.

FIG. 2 is an operation timing chart of transistors and the like which form a motor drive circuit.

FIG. 3 is a diagram illustrating a configuration of a conventional motor drive circuit.

[Explanation of symbols]

TH ... thermistor HIC ... Hall IC Q _1, Q ₂ ... transistors L _1, L ₂ ... motor driving coils _{D 0, D 1, D 2} ... diode D _Z1, D _Z2 ... Zener diode R _1, R ₂ ... resistance t _V , t ₀ ... terminal

Claims (1)

[Claims] 1. In a motor drive circuit for causing a current to flow through a motor drive coil to rotate a rotor, one end of a thermistor is connected to a base of a transistor for controlling a current flowing through the motor drive coil via a diode. Is connected to the ground at the other end thereof and the transistor is connected to the ground through a diode.