JPH07118942B2 - 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 good controllability not only in the acoustic field but also in the information field, and their applications are expanding rapidly. Among them, since the brushless motor has the advantage that it has no brush / commutator contact portion and has a long service life, its application is expanding as an industrial motor in which reliability is particularly important.

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 susceptible to temperature changes and the like, and since the induced voltage of the coils 401 and 402 has a pulsating waveform, 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 the Problems In order to solve the problems described above, the present invention includes a plurality of diodes for absorbing a pulse generated when a current path to a coil is switched, A period measuring circuit for measuring the time period of a pulse, and when the period becomes a predetermined first period or more, energization of the output transistor is stopped, and when the energization stop period becomes a predetermined second period or more, the output transistor is energized. A drive circuit for starting is provided.

Operation According to the above configuration, the rotational position of the rotor is detected by the position detecting means such as the Hall element, and in the motor configuration in which the output transistor is driven through the drive circuit, the time period of the pulse generated when the energizing path is switched is measured. A cycle measuring circuit is provided, and when the time cycle becomes larger than a preset first cycle, the output signal stops the operation of the drive circuit and cuts off the energization of the coil. Further, when the energization stop time becomes longer than the 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, Reference numeral 103 denotes a drive circuit for driving a plurality of output transistors 104 that switch energization to the coil 105 according to the output of the position detection means 102, and 106 measures the time period of a pulse generated when the energization path to the coil 105 is switched. In the cycle measuring circuit, the diode 107 for absorbing the pulse generated when the energizing path is switched, the cycle detecting circuit 108, and the FV converting circuit.
109 and a voltage comparison circuit 110.

Next, a specific configuration of the cycle measuring circuit 106 will be described with reference to FIG. In the figure, output transistors 213 and 214 have collectors connected to each other, emitters connected to Vcc and ground, respectively, and bases connected to output terminals of the drive circuit 212, respectively.

One end of a coil 215 is connected to the connection point between the collectors of the output transistors 213 and 214 (in this figure, only one phase of the three-phase full-wave drive Y connection is shown, and the others are omitted). At the same time, the cathode side of the diode 216 is connected. The base of a transistor 211 whose emitter is connected to the anode side of the diode 216 is connected to the ground via a resistor 210, and the collector is connected to the base of a transistor 208 via a resistor 209. The emitter of the transistor 208 is connected to Vcc and the collector is connected to the base of the transistor 206 via the resistor 207. The emitter of the transistor 206 is connected to the ground, and the collector is connected to one end of the capacitor 205, one end of the constant current source 202, the collector of the transistor 203 and the input terminal of the comparator 219.
The other ends of the capacitor 205 and the constant current source 202 are connected to the ground. The emitter of the transistor 203 is connected to the emitter of the transistor 204 and the constant current source 2
Connected to Vcc through 01. Transistor 204 above
The collector of is connected to ground. The terminal of the comparator 219 is given a reference voltage via a resistor 217, and its output terminal and the inverter 22 via a resistor 2148.
It is connected to the 0 input terminal.

The output terminal of the inverter 220 is connected to the base of the transistor 203 via the resistor 221 and the inverter 2
Connected to 22 input terminals. The output terminal of the inverter 222 is connected to the base of the transistor 204 via the resistor 223 and the transistor 225 via the resistor 224.
Connected to the base of. The emitter of the transistor 225 is connected to the ground, and the collector is the drive circuit.
It is connected to 212 and controls the drive circuit 212.

Next, the operation will be described with reference to FIG. The magnitudes of the currents of the constant current sources 201 and 202 are set so that I ₁ > I ₂ , so that when the transistor 203 is ON, the capacitor 205 has a current of (I ₁ −I ₂ ). Will be charged.

Considering the moment when the output transistor 213 switches from ON to OFF when the motor is rotating normally, the coil
A current is trying to flow through 215 → ground → the above resistor 210 →
A pulse current flows through the transistor 211 and the diode 216. This current causes the transistor 21
The collector current of 1 is the transistor 208 → the resistor 209
Flowing through. Then, the transistor 208 and the transistor 206 are sequentially driven in a pulsed manner. In the case of this example, since there are three phases, it is possible to drive the above-mentioned transistor three times in one rotation by arranging the above diodes 216 for three phases. Assuming that the pulse period obtained at this time is T ₁ , the terminal voltage of the capacitor 202 becomes a sawtooth wave having a peak at V ₃ in FIG. Next, when the rotation of the motor becomes low speed or stopped, the pulse cycle becomes proportionally long, and if the cycle at this time is T ₂ , the terminal voltage of the capacitor 205 reaches the point of V ₁ in FIG. ing. Comparator 21 above
Since the input terminal 9 has a hysteresis (V ₁ -V _{2 in} FIG. 3) determined by the resistors 217 and 218 with respect to the reference voltage, the output terminal becomes H → L at this point. Therefore, the transistor 203 is ON → OFF, the transistor is
204 turns OFF → ON, and the transistor 225 turns ON → OFF.
When the transistor 225 is turned from ON to OFF, the drive circuit 212 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. A predetermined time T _{3 after the} drive circuit 212 is cut off
After that, the terminal voltage of the capacitor 205 becomes V in Fig. 3.
Reach ₂ Then, the output terminal of the comparator 219 becomes L → H, the transistor 203 is OFF → ON, the transistor 204 is ON → OFF, and the transistor 225 is OFF →.
When turned on, the drive circuit 212 is turned on. Therefore, the coil 215 also conducts, and the motor is energized. As described above, the electric charge of the capacitor 205 is forcibly left 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, when the rotation is still slow or stopped, the pulse period is T ₄
In the above case, the terminal voltage of the capacitor 205 reaches V ₁ in FIG. 3 and shuts off the drive circuit 212 again.

By appropriately selecting the values of the current values I ₁ and I ₂ of the constant current sources 201 and 202, the duty ratio of ON / OFF of the drive circuit 212 can be arbitrarily set, and the temperature rise of the coil according to the motor specifications can be prevented. The upper limit can be set easily.

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 THE DRAWINGS FIG. 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. It is a circuit diagram of a prior art example. 101 ... Rotor, 102 ... Position detecting means, 103 ... Driving circuit, 104 ... Output transistor, 105 ... Coil, 106 ...
… Period measurement circuit, 107… Diode.

Claims (3)

[Claims] 1. A position detecting means for detecting a rotational position of a rotor, coils of a plurality of phases, a plurality of output transistors for switching a conduction path to the coil according to an output signal of the position detecting means, and A cycle measuring circuit for measuring a time cycle of a generated pulse including a diode for absorbing a pulse generated when the energization path is switched, and a drive circuit are provided, and the cycle measuring circuit has one capacitor and this capacitor. A constant current source that has a current value I ₁ that charges and discharges electric charge, and a current value I ₂
A constant current type charging / discharging means having a constant current source, and a discharge transistor for forcibly discharging the electric charge of the capacitor by the output signal of the position detecting means at the time of steady rotation, and the drive circuit changes the potential of the capacitor. When it is determined that the first level V ₁ (first cycle) is reached, energization to the output transistor is stopped, and when the second level V ₂ (second cycle) is reached, energization to the output transistor is started. A coil burnout prevention device for a brushless motor, which is characterized in that 2. A third level V ₃ during steady rotation and the second level
A fourth level V ₄ is provided by using an intermediate potential between the _second level V ₂ and a means for issuing a warning 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. The charging / discharging means has two output transistors of a constant current circuit each having different polarities, collectors of which are connected in series via a transistor switch, and one end of a capacitor is connected to the connection point, and the other end is connected. Is connected to or of the power source, and the collector currents of the two output transistors of the constant current circuit are set such that the charging current> the discharging current with respect to the capacitor.
A coil burnout prevention device for a brushless motor according to the item.