JPH0226479B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a brushless DC motor in which current paths to a plurality of coils are electronically switched using transistors.

Conventional configuration and its problems Brushless DC motors do not use a brush commutator, so there is no commutation noise, and they have a long life and high reliability.
Widely used in video equipment. In brushless DC motors used in these devices, the current path to the coil is switched using a non-contact position detector and a plurality of drive transistors that become active in response to the output of the position detector. Furthermore, the operating current (or voltage) of the drive transistor is controlled so that the current supplied to the coil is at a predetermined value (value corresponding to the command signal). As a result, a collector loss occurs in the drive transistor, and the temperature of the transistor increases, resulting in thermal breakdown and shortened lifespan. In addition, when the drive transistor and other main circuit transistors and resistors are integrated into a single silicon chip (IC), the heat generated by the multiple drive transistors is concentrated within the chip, causing thermal damage to the IC. tends to occur. In particular, the higher the temperature of the operating environment, the higher the internal temperature for the same amount of heat generated, which has led to stricter restrictions on the ambient temperature at which the brushless DC motor can be used, posing a major problem in its use.

Purpose of the Invention The present invention takes such points into consideration, detects the temperature of the drive transistor (the transistor that generates the most heat), and corrects the current to be supplied to the coil when the temperature exceeds a predetermined value. The object of the present invention is to provide a brushless DC motor having a protection function that reduces the heat generation of the drive transistor and limits its temperature rise, thereby preventing the transistor from rising in temperature to a temperature that would lead to thermal breakdown. be.

Structure of the Invention In order to achieve the above object, the present invention includes a field means attached to a movable part of a motor, a plurality of coils, and a field means inserted into a current path from a DC power source to the coils for on/off operation. voltage converting means for outputting a DC voltage proportional or substantially proportional to the on-time ratio of the switching transistor to be turned on; a plurality of driving transistors for switching a current path from the output terminal of the voltage converting means to the coil; a position detection means for detecting the position of the part, a command signal generation means for obtaining a command signal, a current detection means for detecting the current supplied to the coil, and a comparison result between the output signal of the current detection means and the command signal. current control means for controlling the conduction current of the drive transistor accordingly; and current input/output of the plurality of drive transistors forming a current supply path from one output terminal side of the voltage conversion means to the plurality of coils. an operation detection means that constantly detects the minimum voltage among the voltage drops between the terminals and controls the on-time duty of the switching transistor according to the detection signal; and a difference between the temperature of the drive transistor and a predetermined temperature. temperature detection means for obtaining a current signal proportional to or approximately proportional to the temperature detection means; and command signal modification means for reducing the command signal in proportion to or approximately proportion to the current signal of the temperature detection means, the voltage conversion means and the operation A temperature limiter configured to control an operating voltage of the drive transistor when energized to a predetermined value by the detection means, and limit a temperature rise of the drive transistor by the temperature detection means, the command signal modification means, and the drive transistor. A transistor, a diode, and a resistor forming a loop and further forming the temperature detecting means are integrated and formed on the same silicon chip as a plurality of the driving transistors.

DESCRIPTION OF EMBODIMENTS The present invention will be described below based on illustrated embodiments. FIG. 1 is an electrical circuit diagram showing one embodiment of the brushless DC motor of the present invention. In Figure 1, 1 is a field magnet attached to the motor moving part (rotor), 2, 3, and 4 are three-phase coils, and 5, 6, and 7 are current paths to coils 2, 3, and 4. 8 is the magnet 1.
9 is a distributor that distributes and controls the energization of the drive transistors 5, 6, and 7 according to the output of the position detector 8, and 10 is a command signal V. A command signal generator 11 generates a signal ₁ , and a temperature detector 11 detects the temperature of the drive transistor (or the temperature of the silicon chip). Further, 12 is an operation detector that detects the operating voltage when the drive transistors 5, 6, and 7 are energized, 13 is a voltage converter that obtains a variable output DC voltage in response to the output of the operation detector 12, and 21 and 22.
is a DC power supply. The operation detector 12 constitutes voltage control means for controlling the output voltage of the voltage converter 13.

Next, its operation will be explained. The speed detector 23 of the command signal generator 10 is composed of, for example, a frequency generator and a period/voltage converter, and reduces the output voltage when the rotation speed of the motor is slow, and reduces the output voltage when the rotation speed reaches a predetermined rotation speed. I'm going to make it bigger.
The output of speed detector 23 is input to current converter 26 and compared with a predetermined voltage level provided by resistors 24 and 25. The current converter 26 is configured by, for example, a differential voltage amplifier and a voltage/current converter, and is configured by connecting the output voltage of the speed detector 23 and a predetermined voltage (resistance 24
and 25 divided voltages), and draws a current i ₁ according to the difference.

The output current i ₁ of the current converter 26 is input to a current mirror circuit consisting of transistors 27, 28, 29 and resistors 30, 31. Now, if the output current i ₃ of the temperature detector 11 is zero, the output i ₂ of the current mirror circuit is proportional to the output i ₁ of the current converter 26 (assuming the values of the resistors 30 and 31 are the same, i ₂ = i ₁
−i ₃ ). Current i ₂ is resistor 32 and capacitor 33
is converted into a command signal V ₁ by The conversion formula is V ₁ =R ₃₂ /1+jωC ₃₃ R ₃₂ ·i ₂ (1), and it has low-pass filter characteristics. Here, R ₃₂ and C ₃₃ are the values of the resistor 32 and capacitor 33, respectively.

The command signal V ₁ is applied to the normal input terminal of the current controller 38 of the distributor 9, and is compared with the output V ₂ of the current detector 40 applied to its inverted input terminal, and a current corresponding to the difference between the two is generated. Output i ₄ . The current controller 38 is composed of, for example, a differential voltage amplifier and a voltage/current converter, and the current i ₄ is selected by a selector 39.
Supplied as a common emitter current. Selector 39
The Hall elements 35, 36, 3 of the position detector 8 are connected to the base terminals of the transistors 41, 42, 43, respectively.
7 output voltages are applied respectively. Hall elements 35, 36, and 37 sense the magnetic flux of magnet 1 and generate analog voltage signals corresponding to its rotational position. The transistors 41, 42, and 43 distribute the common emitter current to each collector current according to the difference in their base voltages, and the collector current of the transistor with the lowest base voltage is the largest, and the collector current of the other transistors is substantially becomes zero.

The collector currents of the transistors 41, 42, 43 become the base currents of the drive transistors 5, 6, 7, are amplified and supplied to the coils 2, 3, 4. The current I _a (current flowing through the drive transistor) supplied to the coils 2 , 3 , and 4 is detected as a voltage drop V ₂ across the resistor 44 of the current detector 40 and input to the current controller 38 .

As a result, the current controller 38, selector 32, drive transistors 5, 6, 7 and current detector 40
, a first feedback loop is configured, and the current I _a supplied to the coils 2, 3, and 4 is reliably set to a value corresponding to the command signal V ₁ (actually, the value of V ₁ shown in the figure is
and V ₂ are controlled so that they are equal).

To explain this, as the command signal V ₁ increases, the output current i ₄ of the current controller 38 increases, the base current and conduction current I _a of the drive transistor selected by the selector 39 increase, and the voltage signal V ₂ is increased and V ₂ becomes equal or almost equal to V ₁ and becomes stable. That is, the current I _a supplied to the coil is I _a =V ₁ /R ₄₄ (2).

Due to the operation of this first feedback loop, the influence of variations in h _FE of the drive transistors 5, 6, and 7 is significantly reduced. Furthermore, as the magnet 1 rotates, the output voltages of the Hall elements 35, 36, and 37 change, and the energization of the drive transistors 5, 6, and 7 is distributed and controlled so that current is supplied to the corresponding coil.
I will switch.

Note that the capacitor 45 is provided for phase compensation (prevention of oscillation) of the feedback loop described above. Also,
a resistor 51 connected in parallel to the coils 2, 3, and 4;
The series circuit of capacitors 53, 55 and capacitors 52, 54, and 56 reduces the spike voltage caused by switching of the energizing path.

Next, the operations of the operation detector 12 (voltage control means) and the voltage converter 13 will be explained. The voltage converter 13 is a switching transistor inserted in a power supply circuit from the positive terminal (V _S = 20V) of the DC power supply 21 to the common connection terminal of the coils 2, 3, and 4 with the emitter-collector path connected in series. 92, flywheel diode 93, and inductance element 94
, a capacitor 95, and a switching controller 91.

The switching controller 91 can utilize various known configurations, such as a sawtooth wave oscillator and a comparator, and obtains a pulse signal with a duty corresponding to the input current _i7 to control the switching transistor 92 on and off.

The output voltage V _M of the voltage converter 13 changes in relation to the on-time ratio (substantive duty ratio) of the switching transistor 92. Output voltage V _M
is supplied to three-phase coils 2, 3, and 4 and drive transistors 5, 6, and 7, and the drive transistors that become active are sequentially switched in accordance with the operation of the distributor 9 described above.

The operation detector 12 detects the operating voltage of the drive transistor in the energized state. Constant current source 74
The current I ₅ is the resistance 75 and the diodes 76, 77, 7
8, and a predetermined voltage value V _3r = R ₇₅ · I ₅ + 3V _D (3) is obtained from the common connection point (emitter terminal) of the drive transistors (when the comparison transistor 79 is off).
One end (base) of each detection transistor 71, 72, 73 is directly connected (directly or via a resistor, diode, etc.) to the output terminal (collector) of each drive transistor 5, 6, 7, and one end (emitter) are commonly connected to the base of the comparison transistor 79, one end (collector) is commonly connected to the lowest potential point (earth potential), and the drive transistors 5, 6, 7 are connected to the emitter connection points of these detection transistors 71, 72, 73. A value corresponding to the operating voltage when energized appears. The comparison transistor 79 outputs a collector current _i6 according to the detected voltage, and the diode 80, the transistor 81, the resistors 82, 83
is inverted and amplified by a current mirror consisting of
Output current i ₇ is sucked from switching controller 91 of voltage converter 13 . Here, if the operating voltage of the drive transistor when it is energized is V _CE , and the base-emitter forward voltage of the corresponding detection transistor and comparison transistor 79 is V _BE , then V ₃ = V _CE + 2V _BE ......(4) V ₃ = _R75・( _I5 − _i6 )+3V _D ……(5), and the collector current of the comparison transistor 79 _i6
As V _BE =V _D , i ₆ = (1/R ₇₅ )・(R ₇₅・I ₅ +V _D −V _CE )……(6). That is, the current i ₆ changes in response to the difference between the operating voltage V _CE when the drive transistor is energized and the predetermined voltage (R ₇₅ · I ₅ + V _D ), and the output of the operation detector 12 changes.
i ₇ changes.

Therefore, a second feedback loop is constituted by the operation detector 12 (voltage control means), the voltage converter 13, and the coils 2, 3, and 4, and detects the operation voltage (when energized) of the aforementioned drive transistor. , so that its operating voltage is equal to or approximately equal to a predetermined value (about 1 V) within the active region.

That is, when the operating voltage of the driving transistor becomes smaller, the collector current i ₆ of the comparison transistor 79 becomes larger, and the output of the operation detector 12 becomes smaller.
i ₇ becomes larger. An increase in i ₇ changes the pulse width of the switching controller 91 of the voltage converter 13, increases the on-time ratio of the switching transistor 92, and increases the output voltage V _M of the voltage converter 13. As a result, feedback is applied to increase the operating voltage of the drive transistor.

If this is done, the operating voltage of the drive transistor is set to a small value within the active region, so its collector loss will be significantly reduced (this effect is especially large when the current _Ia supplied to the coil is small). ). In addition, the switching transistor 9
Since the required output voltage V _M is obtained by turning on and off the voltage converter 2 and the on-time ratio thereof, the loss accompanying voltage conversion by the voltage converter 13 is extremely small. That is, the power efficiency of the motor of this embodiment when operating at a small current is significantly improved.

Next, the operation of the temperature detector 11 will be explained. A constant current source 61, a Zener diode 62, a transistor 63, and resistors 64 and 65 generate a predetermined voltage value V ₄ (approximately 400 mV) with small temperature drift.
Transistor 6 for temperature detection
It is applied to the base of 6. The emitter of the transistor 66 is connected to the other end of the reference voltage V ₄ via a small resistance (approximately 100Ω) resistor 67, and its collector is connected to the transistor 28 of the command signal generator 10.
It is connected to the Emitsuta.

The transistor 66 is arranged in close contact with (thermally coupled to) at least one drive transistor to detect the temperature of the drive transistor (actually, the drive transistors 5, 6, and 7 and the temperature detection transistor 66 are integrated circuits on a single silicon chip).

Now, when the heat generation in the drive transistor increases and its temperature rises, the collector current _i3 of the transistor 66 increases the base-emitter forward voltage.
The relationship of V _BE changes as shown in FIGS. 1-4.

On the other hand, since V ₄ = V _BE(T) + R ₆₇・i ₃ (7), the collector current i ₃ is determined by the V _BE vs. i ₃ characteristic determined by the temperature T and the straight line in Figure 2 (i ₃ = (V ₄ −
V _BE )/R ₆₇ ), and the current i ₃ is the temperature T
change with. Figure 3 shows the relationship between temperature T and _i3 . That is, the collector current of transistor 66
_i3 is the temperature T of the drive transistor at a predetermined value (150
℃) or less, it is zero or approximately zero, and as the temperature T rises, the value gradually increases.

The output _i3 of the temperature detector 11 is the command signal generator 10.
The collector current i ₂ of the transistor 28 flows through the resistor 31, causing a voltage drop across the resistor 31.
(i ₂ = i ₁ − i ₃ ). Decrease in i ₂ is a command signal
By reducing V ₁ and operating the first feedback loop, the current I _a supplied to the coil, and therefore the current flowing through the drive transistor, is reduced. As a result, the heat generation (collector loss) of the drive transistor is reduced,
Temperature rise is limited.

That is, a third feedback loop is formed by the temperature sensor 11, a current correction means responsive to its output _i3 (in this case, a part of the command signal generator 10 and the first feedback loop), and a drive transistor. By controlling the heat generation in the drive transistor, the temperature of the drive transistor is limited from increasing excessively (temperature limit loop). As a result, even when the ambient temperature of the usage environment is high, thermal damage to the drive transistor can be prevented.

In addition, this third feedback loop simply limits the temperature rise of the drive transistor, and even when this loop is operating (when the temperature of the drive transistor exceeds 150°C), current flows through the coil. Supplied. Therefore, even if the ambient temperature is high and the motor load is somewhat heavy, the magnet 1
Accelerating torque is generated by the magnetic flux of the motor and the current _Ia flowing through the coils 2, 3, and 4, and the motor is reliably started and accelerated and shifts to a speed control state.

Further, the embodiment shown in FIG. 1 is suitable for integration into an integrated circuit, and includes transistors such as drive transistors 5, 6, 7, distributor 9, command signal generator 10, temperature detector 11, motion detector 12, etc. Diodes and resistors can be integrated and formed on a single silicon chip.
In particular, it is preferable that the drive transistors 5, 6, and 7 and the temperature detection transistor 66 be integrated circuits.

Further, in the embodiment shown in FIG. 1, the operation voltage V _CE of the drive transistor when it is energized is controlled to a predetermined small value (about 1 V) by the operation of the second feedback loop. Therefore, the heat generation in the drive transistor (collector loss P _C =V _CE・I _a ) becomes smaller, and the relationship of heat generation to changes in I _a (or V ₁ ) becomes linear (proportional), and the above-mentioned third condition is satisfied. The feedback loop can be constructed from linear elements,
It also has the effect of stabilizing its operation.

FIG. 4 shows an electric circuit diagram representing another embodiment of the present invention. In this embodiment, a current mirror consisting of transistors 101 and 102 is added to the temperature detector 11, and the output current _i8 is passed through the resistor 104 of the current corrector 103 of the distributor 9, so that the value of _i8 is adjusted. The current I _a supplied to the coil (current flowing through the drive transistor) is adjusted accordingly. The configuration and operation of other parts are the same as those of the embodiment shown in FIG. 1 described above, and their explanation will be omitted.

In FIG. 4, the current I _a to the coil is controlled so that V ₁ = V ₂ by the operation of the first feedback loop, but when the temperature detector 11 operates (i ₈ >
0) V ₂ = R ₄₄ · I _a + (R ₁₀₄ + R ₄₄ ) i ₈ ......(8). Therefore, from V ₁ = V ₂ , I _a = (1/R ₄₄ )・[V ₁ − (R ₁₀₄ − R ₄₄ ) i ₈ ]……(9
), and the current I _a to the coil decreases in accordance with the output i ₈ of the temperature detector 11. That is, temperature sensor 1
1. Current correction means (current corrector 103 and first
(feedback loop) constitutes the aforementioned third feedback loop.

Note that the value R ₁₀₄ of the resistor 104 is the value R ₄₄ of the resistor 44.
100 times or more, so that the output _i8 of the temperature detector 11 may be large.

In each of the embodiments described above, the output voltage V _M of the voltage converter 13 is controlled so that the drive transistor operates within the active region, and the required current is applied to the coil by controlling the current flowing through the drive transistor. I started supplying it. However, the present invention is not limited to such a case, and can be implemented even when the drive transistor operates on and off (saturation and cutoff). An electrical circuit diagram representing an embodiment of such a brushless DC motor is shown in FIG. In Fig. 5, a field magnet 1, a three-phase coil 2,
3, 4, drive transistors 5, 6, 7, position detector 8, command signal generator 10, temperature detector 11, voltage converter 13, and DC power supplies 21, 22 are the same as those in the embodiment shown in FIG. be. In this embodiment, the distributor 9 includes a constant current source 105 and a selector 39, and distributes the current of the current source 105 to the base of the drive transistor corresponding to the output of the position detector 8. 5, 6, and 7 are controlled on and off, and current I _a is supplied to the necessary coils as the motor rotates.

The currents supplied to the coils 2, 3, and 4 are detected by the current detector 40 of the voltage controller 14, and a voltage _V2 corresponding to the current _Ia supplied to the coils is obtained. The detected voltage V ₂ is compared with the command signal V ₁ by the comparator 106, and a current i ₇ corresponding to the difference between the two is drawn from the switching controller 91 of the voltage converter 13. Therefore, the output voltage V _M of the voltage converter 13
is a value corresponding to the output current _i7 of the voltage controller 14. That is, the current detector 40 of the voltage controller 14
The comparator 106, the voltage converter 13, and the coils 2, 3, and 4 constitute a feedback loop that makes the current I _a to the coil a value corresponding to the command signal V ₁ (actually, V ₂ = V ₁ ). As a result, drive transistors 5, 6, 7
This greatly reduces the influence of variations in the saturation voltage of the coil, and ensures that the current I _a supplied to the coil is a value that corresponds to the command signal V ₁ .

When the temperature of the drive transistor 5, 6, or 7 exceeds a predetermined value due to heat generation (collector loss due to saturation voltage V _{CE (sat)} and current I _a ), the temperature detector 11 operates and its output current i Increase ₃ .
When i ₃ becomes large, the command signal V ₁ is made small, and the supply current I a to the coil is _reduced by the operation of the feedback loop described above.
Make smaller. As a result, the heat generated by the drive transistor when energized is reduced, and excessive temperature rise is restricted. That is, a temperature detector 11, a current correction means responsive to its output _i3 (here, a part of the command signal generator 10 and the aforementioned feedback loop),
A feedback loop is formed by the drive transistor to prevent the temperature of the drive transistor from rising excessively beyond a predetermined value.

Note that, as shown in the embodiment of FIG. 2, also in this embodiment, the detected voltage V ₂ side may be corrected based on the output i ₃ of the temperature detector 11.

It goes without saying that the present invention is not limited to rotary brushless DC motors that perform rotational motion, but can also be applied to so-called linear brushless DC motors in which the movable parts of the motor move linearly relative to each other. Further, the present invention is not limited to a motor having three-phase coils, but can generally be configured to have a plurality of coils. Furthermore, various known methods can be used for the position detection means.

Furthermore, the driving transistors 5, 6, 7 and the switching transistor 92 are not limited to bipolar transistors, but other transistors such as field effect transistors may be used.

Further, in each of the embodiments described above, the output voltage V _M of the voltage converter 13 is lower than that of the DC power supply 21, but the present invention is not limited to such a case, and the present invention is not limited to such a case. It may be converted and supplied to the coil. Further, the configuration of the voltage converter may employ various methods and configurations such as an inverter type, a frequency modulation type chopper type, and a pulse width modulation type chopper type.

In addition, various modifications are possible without changing the gist of the present invention.

Effects of the Invention As is clear from the above description, the brushless DC motor of the present invention has the following advantages: (a) The operation of the temperature limiting loop does not cause an excessive temperature rise in the drive transistor, so thermal destruction of the drive transistor can be prevented. (b) Since the operating voltage of the drive transistor when energized is controlled to a predetermined small value, heat generation is proportional to the energization current of the drive transistor,
The operation of the temperature limit loop becomes stable. (c) Even when the temperature limit loop is operating due to a rise in the temperature of the drive transistor, current is supplied to the coil (the current value is small). , if the load torque is small, the motor stably starts and accelerates and enters the controlled state. (d) Since the transistor, diode, and resistor of the temperature detection means are integrated on the same silicon chip as the drive transistor, the temperature of the drive transistor can be detected. This has the effect of making it easier and more reliable. Therefore, if a capstan motor or reel motor of a video tape recorder or the like is constructed based on the present invention, the reliability of the equipment will be significantly increased.

[Brief explanation of drawings]

FIG. 1 is an electrical circuit diagram showing one embodiment of the present invention, FIGS. 2 and 3 are diagrams for explaining the operation of the temperature detector, and FIG. 4 is an electrical circuit diagram showing another embodiment of the present invention. Circuit Diagram FIG. 5 is an electrical circuit diagram representing another embodiment of the present invention. 1... Field magnet, 2, 3, 4... Coil, 5, 6, 7... Drive transistor, 8...
Position detector, 9... Distributor, 10... Command signal generator, 11... Temperature detector, 12... Operation detector, 13... Voltage converter, 14... Voltage controller,
21, 22...DC power supply.

Claims (1)

[Claims] 1. Field means attached to the motor movable part,
a plurality of coils, and a voltage conversion means that outputs a DC voltage proportional or substantially proportional to the on-time ratio of a switching transistor inserted in a current path from a DC power supply to the coil and operating on and off;
a plurality of drive transistors that switch a current path from the output terminal of the voltage conversion means to the coil;
a position detection means for detecting the position of the motor movable part; a command signal generation means for obtaining a command signal; a current detection means for detecting the current supplied to the coil; current control means for controlling the current flowing through the drive transistor according to a comparison result; and a plurality of drive transistors forming a current supply path from one output terminal side of the voltage conversion means to the plurality of coils. an operation detection means that constantly detects the minimum voltage among the voltage drops between the current input and output terminals, and controls the on-time duty of the switching transistor according to the detection signal; temperature detection means for obtaining a current signal proportional or approximately proportional to the temperature difference; command signal modification means for reducing the command signal in proportion or approximately proportion to the current signal of the temperature detection means; The operation detection means is configured to control the operating voltage of the drive transistor to a predetermined value when energized, and the temperature detection means, the command signal modification means, and the drive transistor limit a temperature rise of the drive transistor. A brushless DC motor comprising a temperature limiting loop and further comprising a transistor, a diode, and a resistor constituting the temperature detecting means, which are integrated on the same silicon chip as a plurality of the driving transistors.