JPH07118941B2 - Brushless motor coil burnout prevention device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor, and more particularly to an automatic recovery type coil burnout prevention device.

2. Description of the Related Art In recent years, small DC motors have been recognized for their excellent controllability not only in the acoustic field but also in the information field, and their applications are expanding rapidly. Among them, the DC brushless motor has an advantage that it has a long service life because it does not have a brush / commutator contact portion, and therefore its application as an industrial motor where reliability is particularly important is expanding.

Under such circumstances, the drive system of small axial fans has been switched from AC to DC for the past several years, and DC axial fans that use brushless motors are increasing.

As the packaging density of industrial equipment such as computer-related equipment has increased, the DC axial fan has been required for cooling the fan and has required higher reliability. In other words, if the motor stops for any reason, it will not only prevent the motor coil from burning out, but it will also give an alarm to the device itself to prevent an accident, and will automatically recover when the cause is removed. It has come to be required to rotate normally.

A conventional example of a coil burnout prevention device used in a DC axial fan motor will be described with reference to FIG.

In FIG. 4, coils 401 and 402, output transistor 40
2 with 5 and 406, drive transistors 407 and 408, and resistor 409
It constitutes a half-wave drive motor. That is, it is assumed that the control transistor 410 is conductive now. Switch 417 at this time
Is connected to the base of the drive transistor 407 to introduce a tribe current, the resistance 409 → drive transistor 4
The drive current flows through the path of 07 → output transistor 405, and the coil 401 becomes conductive. Conversely, switch 4 above
When 17 is connected to the base of the drive transistor 408 and a drive signal is introduced, a tribe current flows through the path of the resistor 409 → the drive transistor 408 → the output transistor 406, and the coil 402 becomes conductive. Thus coil 4 above
By alternately conducting 01 and 402, the motor can rotate. However, with this circuit alone, when the motor is stopped due to an external factor or is operating at a low speed with an overload, the coils 401 and 402 are burned by the excessive current and the function of the motor cannot be achieved. In order to eliminate these problems, the control transistor 410 is cut off by the following circuit configuration to prevent an excessive current from flowing. That is, the diode 403 is connected to the coil 4 from the connection point between the coil 401 and the collector of the output transistor 405.
The induced voltage of the coils 401 and 402 is led from the connection point between 02 and the collector of the output transistor 406 via the diode 404, and the capacitor 415 is charged via the resistor 413. In the case of steady rotation, the induced voltage of the coils 401 and 402 is sufficiently high, so the charging voltage of the capacitor 415 exceeds the reference voltage and the output of the comparator 412 becomes L level. Therefore, a current flows in the order of the base of the control transistor 410, the resistor 411, and the comparator 412, and the control transistor 410 is turned on. On the contrary, when the coil is stopped or rotated at low speed, the induced voltage of the coils 401 and 402 becomes small, so that the charging voltage of the capacitor 415 becomes lower than the reference voltage and the output of the comparator 412 becomes H level. Therefore, the control transistor 410 is cut off, and the energization of the coils 401 and 402 is also cut off. In this way, burnout of the coils 401 and 402 is prevented.

Problems to be Solved by the Invention However, a drawback of this method is that once the system is cut off, it cannot be automatically restarted even if the obstacle is removed. Further, since it is an analog operation, it is easily affected by temperature changes and the induced voltage of the coils 401 and 402 has a pulsating waveform, so that it is necessary to set a large time constant, and the capacitor 415 having a large capacitance is not used. The accuracy of the shut-off operation is poor.

Means for Solving Problems In order to solve the problems described above, in the present invention, a cycle measuring circuit for measuring the time cycle of the output signal of the position detecting means for detecting the rotational position of the rotor, A drive circuit is provided which stops the energization of the output transistor when the cycle becomes a predetermined first cycle or more and starts the power supply of the output transistor when the energization stop period becomes a predetermined second cycle or more.

Operation According to the above configuration, in the motor configuration in which the position detecting means such as the Hall element detects the rotational position of the rotor and drives the output transistor through the drive circuit, the time period of the output signal of the position detecting means is changed to the cycle measuring circuit. Measured
When the time period becomes longer than the preset first period, the operation of the drive circuit is stopped by the output signal, and the power supply to the coil is cut off. Further, when the energization stop time becomes longer than a preset second cycle, the drive circuit is automatically operated to re-energize the coil.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the basic configuration of the present invention, 101 is a rotor composed of magnets magnetized in multiple poles, 102 is a position detecting means for detecting the rotational position of the rotor 101 and outputting a rotational position signal, 103 is a drive circuit that drives a plurality of output transistors 104 that switch the energization path to the coil 105 according to the output of the position detection means 102, and 106 is a cycle measurement circuit that measures the time cycle of the output signal of the position detection means 102. , Cycle detection circuit 10
7, an F-V conversion circuit 108, and a voltage comparison circuit 109.

Next, a specific configuration of the cycle measuring circuit 106 will be described with reference to FIG. In the figure, a logic gate 209 has its first input terminal connected to the input terminal of the inverter 212 and also to the output terminal of the position detecting means 102, and its second input terminal via a resistor 211 to the inverter 212. In addition to connecting to the output terminal, a capacitor 210 is connected between the second input terminal and the ground, the output terminal of which is Vc via a resistor 208.
transistor 206 via resistor 207
Connected to the base of. The emitter of the transistor 206 is connected to ground, and the collector is the capacitor 205.
Also, it is connected to one end of the constant current source 202 and to the input terminal of the comparator 215 and the collector of the transistor 203. The other ends of the constant current source 202 and the capacitor 205 are connected to the ground. A terminal of the comparator 215 is supplied with a reference voltage via a resistor 213 and is connected to its output terminal via a resistor 214, and the output terminal is an inverter 216 and the transistor via a resistor 218.
It is connected to the base of 203. The output terminal of the inverter 216 is a transistor via an inverter 217 and a resistor 220.
221 is connected to the base. The connection point between the output terminal of the inverter 217 and the resistor 220 is connected to the base of the transistor 204 via the resistor 219. The collector of the transistor 204 is connected to ground, the emitter is connected to the emitter of the transistor 203, and is also connected to Vcc via the constant current source 201. Above transistor
The emitter of 221 is connected to the ground, and the collector is connected to the drive circuit 103 to control the drive circuit 103. Next, the operation will be described with reference to FIG.
Since the magnitudes of the currents of the constant current sources 201 and 202 are set so that I ₁ > I ₂ , the transistor 203 is turned on.
At this time, the capacitor 205 is charged with a current of (I ₁ −I ₂ ).

When the motor is rotating normally now, the position detecting means
If the cycle of the output signal of 102 is T ₁ , then the logic gate 209
From the output terminal, a differential pulse of period T ₁ is obtained. Since the base of the transistor 206 is driven by this differential pulse, the terminal voltage of the capacitor 205 becomes a sawtooth wave having a peak at V ₃ in FIG. Next, assuming that the rotation of the motor becomes low speed or stopped and the cycle of the output signal of the position detecting means 102 becomes T ₂ or more, similarly, the differential pulse of the cycle T ₂ or more is output from the output terminal of the logic gate 209. Is obtained. At this time, the terminal voltage of the capacitor 205 has reached the point of V ₁ in FIG. Since the terminal of the comparator 215 has a hysteresis (V ₁ -V _{2 in} FIG. 3) determined by the resistors 213 and 214 with respect to the reference voltage, the output terminal becomes H → L at this point.

Therefore, the transistor 203 turns ON → OFF, the transistor 204 turns OFF → ON, and the transistor 221 turns ON → OFF. When the transistor 221 is turned from ON to OFF, the drive circuit 103 is cut off and the coil current becomes non-conductive. Further, the current from the constant current source 201 is bypassed by the transistor 204, and the capacitor 205 is stopped,
The terminal voltage drops because it is left unattended by the constant current source 202. When a predetermined time T ₃ has elapsed after the drive circuit 103 was cut off, the terminal voltage of the capacitor 205 reaches V ₂ in FIG. Then, the output terminal of the comparator 215 is L
→ H, the transistor 203 is OFF → ON, the transistor 204 is ON → OFF, and the transistor 221 is OFF → ON
Then, the drive circuit 103 becomes conductive. Therefore, the coil 105 also conducts and the motor is energized. As described above, the electric charge of the capacitor 205 is forcibly discharged by the transistor 206, and when the motor recovers to the steady rotation, it becomes a sawtooth wave having a peak at V ₃ in FIG. However, if the rotation is still slow or stopped and the output signal of the position detecting means 102 is equal to or longer than the period T ₄ , the terminal voltage of the capacitor 205 reaches V _I in FIG. 3 and shuts off the drive circuit 103 again. To do.

By appropriately selecting the current values I ₁ and I ₂ of the constant current sources 201 and 202, the ON / OFF duty ratio of the drive circuit 103 can be arbitrarily set, and the upper limit of the temperature rise of the coil according to the motor specifications can be set. Can be easily determined.

EFFECTS OF THE INVENTION As described above, in the case of the conventional example, once the drive circuit is cut off, it cannot be restarted unless the power is turned on again, but according to the present invention, it is automatically restarted. be able to. Further, in the method of detecting the induced voltage in the coil as in the conventional example, since it is an analog operation, it is easily affected by temperature changes, etc., and since the induced voltage is a pulsating waveform, a smoothing capacitor with a large capacitance must be used. However, the accuracy of the shut-off operation was poor, such as a large time constant and poor responsiveness.However, in the case of the present invention, since the time period is detected, it becomes a digital operation and is less susceptible to temperature changes and the like. The smoothing capacitor is unnecessary, the responsiveness is fast, the accuracy of the shutoff and recovery operations is significantly improved, and the practical effect is great.

[Brief description of drawings]

1 is a block diagram of the present invention, FIG. 2 is a circuit diagram of a cycle measuring circuit according to an embodiment of the present invention, FIG. 3 is an operation explanatory diagram of the present invention, and FIG. 4 is a circuit diagram of a conventional example. . 101 ... Rotor, 102 ... Position detecting means, 103 ... Driving circuit, 104 ... Output transistor, 105 ... Coil, 106 ...
… Period measurement circuit.

Claims (3)

[Claims] 1. A position detecting means for detecting a rotational position of a rotor of a DC motor, a plurality of phases of coils, and a plurality of output transistors for switching an energization path to the coil according to an output signal of the position detecting means. And a cycle circuit for measuring the time period of the output signal of the position detecting means, and a drive circuit. The cycle measuring circuit has one capacitor and a current value I ₁ for charging and discharging the capacitor. A constant current source
Constant current type charging / discharging means having a constant current source with a current value I ₂ ,
The drive circuit is provided with a discharge transistor for forcibly discharging the electric charge of the capacitor in response to the output signal of the position detecting means during steady rotation, and the drive circuit determines the potential of the capacitor to determine the first level V ₁ (first cycle). (4), the energization of the output transistor is stopped, and the energization of the output transistor is started when the second level V ₂ (second period) is reached. 2. A third level V ₃ during steady rotation and the second level
Providing a _fourth level V ₄ by utilizing an intermediate potential between the _second level V ₂ and the means for issuing an alarm signal for the coil burnout when the capacitor potential exceeds the fourth potential level. A coil burnout prevention device for a brushless motor according to claim 1. 3. As the charging / discharging means, two output transistors of a constant current circuit have different polarities, their collectors are connected in series via a transistor switch, and one end of a capacitor is connected to the connection point. The other end is connected to or of a power source, and the collector currents of the two output transistors of the constant current circuit are conditionally set to the capacitor such that charging current> discharging current. Coil burnout prevention device for brushless motors.