JPS6249837B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a brushless DC motor that uses transistors to sequentially switch power supply to coils of multiple phases in accordance with the rotational position of a rotor.

Brushless DC motors have low torque ripple, no noise caused by brushes, and have a long life, so they are used in various audio equipment. For example, recently, it has been used as a reel motor of a tape recorder by being directly connected to a reel drive shaft. In the case of a reel motor, high-speed rotation with a short startup time is required during early winding, and the current supplied to the motor is set to be large. In this case, as the back electromotive force increases as the rotation of the motor increases, the drive transistor becomes transiently oversaturated, causing instability in circuit operation and an increase in current ripple. Current ripples have been a major problem because they cause ripples in the generated torque, causing vibration and noise in the motor.

In addition, in motors with speed control,
At the time of startup and acceleration, the drive transistor becomes oversaturated, causing vibrations and noise, as well as deteriorating control pull-in characteristics, which has become a problem.

The present invention aims to improve the operating voltage of the drive transistor (collector-emitter voltage in bipolar transistors,
In a field effect transistor, the voltage between the drain and the source is detected and the supply current is changed to prevent oversaturation. In particular, the detection threshold level is changed in response to a command signal. By doing so, the detection level is increased at the time of large current to correct the saturation characteristics of the transistor, improving the characteristics and providing a breathless DC motor suitable for use in semiconductor integrated circuits (ICs).

The configuration of the present invention will be explained below based on the drawings.
FIG. 1 is an electrical circuit diagram representing one embodiment of the present invention. In FIG. 1, 11 is a field magnet with N and S poles magnetized; 12, 13, and 14 are three-phase coils that interlink with the magnetic flux of magnet 11;
5, 16, and 17 are Hall elements that detect the rotational position of the rotor using the magnetic flux of the magnet 11, and 18 is a speed-voltage converter that obtains a voltage corresponding to the rotational speed of the rotor (the speed detection method and the conversion method to voltage are well-known). technology), 20 is a voltage, current converter,
43, 44, 45 are Hall elements 15, 16, 17
48, 49, 50 are three-phase coil 1, which distributes the common emitter current according to the output of the three differential amplifiers.
57 is a current detection resistor that detects the sum of the currents supplied to the three-phase coils 12, 13, and 14 as a voltage drop; 72 is a current detection resistor that supplies current to the three-phase coils 12, 13, and 14; This is a power supply stop signal that stops power supply to 14.

Note that the portion surrounded by the illustrated broken line is a circuit portion that performs saturation detection and current correction operations, and detailed operations thereof will be described later.

First, normal operation (excluding saturation detection and current correction) will be explained. A command voltage signal 19 corresponding to the rotational speed of the rotor is obtained by a speed-voltage converter 18 having a well-known configuration. The command signal 19 is input to the voltage/current converter 20 and changes the voltage value of the DC voltage source 21.
It is compared with Er, and a current i ₀ corresponding to the difference between the two is drawn into the output terminal of the voltage/current converter 20.

FIG. 2 shows the configuration of the voltage/current converter 20.
This consists of a constant current source 105, a Darlington-connected differential amplifier (transistors 102, 103, 1
07, 108, resistance 101, 104, 106, 1
09) Current mirror circuit (transistor 11
0,111), a common base transistor 113, and its base resistor 112, and when the command signal 19 becomes smaller than Er, the transistor 113 absorbs a current i ₀ corresponding to the difference. Note that the transistor 70 is turned on and off in response to the power supply stop signal 72, and is normally in the off state, but when the power supply is stopped (when the voltage of 72 is high), the transistor 70 is turned on, and the intake current of the transistor 113 is reduced. Set i ₀ to zero regardless of the value of the command signal 19.

The current i ₀ of the voltage/current converter 20 is passed through a current mirror circuit (transistors 22, 23, 24, 25,
The output current is supplied to resistors 26, 27, and 28.
Set i ₁ and i ₂ to values corresponding to current i ₀ . When the saturation detection operation is not performed, the transistor 30 is in an off state (i ₃ =0), and the currents i ₁ and i ₂ are both equal to i ₀ .

Current i ₁ flows through resistor 35 and generates a voltage drop across it. This becomes the base voltage of the transistor 37, and depending on its increase or decrease, the three-phase coil 12,
The combined supply current to 13 and 14 increases or decreases, and the resistor 35
The voltage drop across the resistor 57 is made equal to the voltage drop across the resistor 57. As a result, Ia=R ₃₅ /R ₅₇ i ₁ (1). Here, R ₃₅ is the resistance value of the resistor 35, and R ₅₇ is the resistance value of the resistor 57.

To explain this, as the current _i1 increases, the base voltage of the transistor 37 increases, the base-emitter voltage increases, and the emitter current increases.
Collector current increases. This collector current is inverted by a current mirror circuit (transistor 42, diode 40, resistors 39, 41) and is supplied as a common emitter current of three differential transistors 43, 44, 45. Transistor 43, 4
Hall elements 15 and 1 are connected to the base terminals 4 and 45, respectively.
6 and 17 are applied, and the common emitter current is distributed to each collector current according to the base voltage. As a result, the largest collector current flows through the transistor with the lowest base voltage, and the collector currents of the other transistors have relatively small values. Furthermore, as the rotor rotates, the output voltages of the Hall elements 15, 16, and 17 change smoothly, and the three differential transistors that become active also switch smoothly.

The collector currents of the three differential transistors 43, 44, 45 are connected to the drive transistors 48, 4, respectively.
9 and 50, the current is amplified and supplied to the coils 12, 13, and 14 of each phase. As a result, current is applied to the coils corresponding to the output signals of the Hall elements 15, 16, and 17, thereby ensuring smooth and reliable rotation of the motor. Furthermore, an increase in the common emitter current of the three differential transistors 43, 44, and 45 causes an increase in the current supplied to the three-phase coils 12, 13, and 14.

The combined power supply current to the three-phase coils 12, 13, and 14 is detected as a voltage drop across the current detection resistor 57, and is supplied to the emitter of the transistor 37.
As a result, transistor 37, current mirror circuit (transistor 42, diode 40, resistor 3
9, 41) 3 differential transistors 43, 44, 4
5. A first negative feedback loop (current feedback loop) is configured by the drive transistors 48, 49, 50 and the current detection resistor 57, and the drive transistor 4
8, 49, and 50 due to _hFE variations are made small so that the current supplied to the coils 12, 13, and 14 of each phase becomes a value that effectively corresponds to the command current _i1 . That is, the forward voltage of the diode 36 and the base-emitter voltage of the transistor 37 cancel each other out, and the voltage drop across the resistor 35 is substantially reduced.
R ₃₅ ·i ₁ and the voltage drop R ₅₇ ·Ia of the resistor 57 become equal.

Next, the operation of the saturation detection/current correction means (shown by the broken line in FIG. 1) will be explained. transistor 25
The collector current _i2 is supplied to the diodes 55, 56 and the resistor 54, and the drive transistors 48, 49,
A predetermined voltage value (approx.
(about 1.7V) creates a shifted reference potential point A. These transistors 25, resistors 28,
The diodes 55, 56 and the resistor 54 constitute a reference voltage generating means. The input terminal side (emitter) of each detection transistor 51, 52, 53 is DC-connected (directly or via a resistor) to the reference potential point A, and each detection transistor 5
The detection terminal sides (bases) of transistors 1, 52, and 53 are connected to the output terminals (collectors) of each drive transistor 48, 49, and 50 in a DC manner (directly or via a resistor). Detection transistors 51, 52, 5
Since the forward voltage between the emitter and base of No. 3 is approximately 0.7V, the operating voltage between the collector and emitter of the drive transistor (for example, No. 48) in the energized state is approximately 0.7V.
When the voltage falls below 1V (=1.7V-0.7V), the detection transistor 51 changes from an off state to an active state and supplies current to the collector side. That is, each detection transistor 51, 52, 53 detects saturation (operating voltage becomes below a predetermined value) of each drive transistor 48, 49, 50, and supplies a collector current according to the degree of saturation.

The output currents of the detection transistors 51, 52, and 53 are combined and supplied to a current mirror amplifier circuit (composed of a transistor 30, a diode 29, and resistors 31, 32, and has an amplification gain of 2 to 3), and is A current i ₃ is passed through the resistor 27. When the current _i3 flows, a voltage drop occurs across the resistor 27, so the collector current of the transistor 24
i ₁ decreases, and the current flowing through the drive transistors 48, 49, 50, that is, the current supplied to the coils 12, 13, 14 decreases due to the operation of the current feedback loop described above. As a result, coils 12, 13, 1
4 is reduced and the voltage drop across drive transistor 4 is reduced.
8, 49, and 50 are increased.

That is, the detection transistors 51, 52, 5
3. Current mirror amplifier circuit (transistor 3
0, diode 29, resistor 31, 32), resistor 2
7, driven transistors 48, 49, 5 by transistor 24, resistor 35 and current feedback loop
A second negative feedback loop (saturation detection loop) is configured to prevent oversaturation of zero. In addition, all operating voltages of drive transistors 48, 49, and 50 are
If the voltage is 1V or more, the detection transistor 51,
52 and 53 are all in the OFF state, the above-mentioned negative feedback operation is not performed and current corresponding only to the command signal 19 is supplied to the coils 12, 13, and 14 of each phase.

Note that 33 is a phase compensation capacitor for the saturation detection loop described above, and also functions as a low-pass filter on the command signal side. The transfer function of current/voltage conversion to the base terminal of the transistor 37 is R ₃₅ /1+SC ₃₃ (R ₃₄ +R ₃₅ )...(2)
Here, C ₃₃ is the capacitance value of the capacitor 33, R ₃₄ is the resistance value of the resistor 34, and R ₃₅ is the resistance value of the resistor 35.

Furthermore, the capacitor 33 in this embodiment is
This has the effect of slowing down the change in the power supply current when starting and stopping the power supply to each phase coil 12, 13, 14. To explain this, when the power supply stop signal 72 becomes high, the output current i ₀ of the voltage/current converter 20 suddenly becomes zero. If there is no capacitor 33, the sudden change in i ₀ is i ₁
This results in a sudden change in the current supplied to the coil. Coils 12, 13, 14 for each phase
has a fairly large inductance component, so if the supply current changes suddenly, a sharp whisker-like spike voltage will be generated. coil 12,1
Capacitors 58, 6 connected in parallel to 3, 14
0, 62 and resistors 59, 61, and 63 are damping CRs for absorbing spike voltages, but they cannot sufficiently remove spike voltages when there is no steep current or interruption of large current. As a result, drive transistors 48,4
High voltage is applied to the parts 9 and 50, which is undesirable as it causes voltage breakdown, deterioration, shortened lifespan, etc. Also capacitor 3
3 forms a low-pass filter, so coil 1
The change in the power supply current Ia to 2, 13, and 14 becomes gradual, and the above-mentioned spike voltage becomes an extremely small value.

Note that 38 is a phase compensation capacitor of the current feedback loop. Further, the collector of the transistor 30 may be connected to the collector side of the transistor 24.

FIG. 3 shows the characteristics of the operating voltage V _CE of the drive transistors 48, 49, 50 and the supply current Ia due to the operation of the saturation detection loop. From this, it can be seen that as V _CE decreases, the power supply current Ia decreases rapidly.

Furthermore, as shown in the embodiment of the present invention, since the voltage at the reference potential point A, which is the threshold for saturation detection, is changed in response to the command current _i0 , the threshold voltage increases when a large current is commanded. Also, when a small current command is given, the threshold voltage becomes small, correcting the saturation voltage characteristics with respect to the collector current of the transistor. As a result, the saturation detection operation described above becomes reliable.

In the embodiment described above, three detection transistors 5
1, 52, 53 for each drive transistor 4
Although the operating voltages of 8, 49, and 50 are detected respectively, the present invention is not limited to such a case, and the saturation of one drive transistor may be detected. A specific example is shown in FIG. Here, only the saturation of the drive transistor 48 is detected, and a capacitor 120 is connected to the collector side of the detection transistor 51 to smooth the output and hold it until the next detection point. The capacitor 120 also serves as a phase compensation capacitor for the saturation detection loop.

Furthermore, the configuration shown in the present invention (shown by the broken line in FIG. 1) uses only resistors, transistors, and diodes, making it an optimal circuit configuration for IC implementation. Further, the phase compensation capacitor 33 is connected to the command signal 19.
It is also effective to use a low-pass filter and a gentle change in current when the power supply is stopped. Incidentally, if the speed voltage converter 18 of the above-mentioned embodiment is omitted and the command voltage signal 19 is set to a constant voltage, it can be used for driving a reel motor of a tape recorder or the like. Furthermore, the same configuration can be achieved using not only bipolar transistors but also field effect transistors. It goes without saying that various other modifications can be made without changing the spirit of the invention.

As described above, according to the present invention, the saturation detection and current correction means are provided to reduce the power supply current so as to reduce the degree of saturation of the drive transistor, so that the current distribution during startup and acceleration is smooth, and current ripple (especially, The ripple at the time of switching of the coil to be energized is significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing an embodiment of the present invention;
FIG. 2 is a specific configuration diagram of the _voltage /current converter shown in FIG. FIG. 2 is an electrical circuit diagram showing an example. 11... Field magnet, 12, 13, 14...
... Coil, 15, 16, 17 ... Hall element, 1
8...Speed voltage converter, 19...Command signal, 20
...Voltage/current converter, 48, 49, 50... Drive transistor, 51, 52, 53... Detection transistor, A... Reference potential point.

Claims (1)

[Claims] 1 A rotor having a field magnet, a multi-phase coil interlinked with the magnetic flux of the field magnet, a position detection means for detecting the rotational position of the rotor, and a rotor for detecting the rotational position of the rotor according to an output signal of the position detection means. A drive transistor group for controlling power supply to the coils of a phase, a command signal generation means for commanding a current value to be applied to the drive transistor group, a reference voltage generation means for obtaining a reference voltage signal, and an operation when the drive transistor is energized. The reference voltage generating circuit includes a saturation detection means that operates when the voltage becomes smaller than the reference voltage value, and a current correction means that can change the value of current flowing through the coils of each phase in accordance with the operation of the saturation detection means. The means is adapted to change its reference voltage value in response to the command signal, and the detection threshold level of the saturation detection means is set to be large when a large current command is given and to be small when a small current command is given. Brushless DC motor.