JPS6223554B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a brushless motor drive circuit,
It is particularly suitable for application to three-phase bidirectional current-carrying brushless motors.

FIG. 1 shows a conventional drive circuit for a three-phase bidirectional brushless motor. This motor has three-phase star-connected coils 1A, 1B,
Equipped with 1C. The A-phase coil 1A has a pair of
It is driven by a single-ended push-pull circuit consisting of PNP and NPN transistors T1 and T2, and similarly the B-phase coil 1B is driven by transistors T3 and
The C-phase coil 1C is push-pull driven by T4 and by transistors T5 and T6, respectively. Transistors T1-T6 are turned on and off by control transistors T7-T12, and these transistors T7-T12 are turned on and off by a current switching signal formed in response to a rotor rotational position detection signal.

For example, when the control transistors T8 and T9 are turned on, the drive transistors T1 and T4 are turned on, and as shown by the thin line in FIG. 1, T1, coil 1A, coil 1B, etc.
A driving current is passed through T4 over an electrical angle of 60°. Another pair of drive transistors is then turned on one after the other, causing one rotation of the motor in six cycles.

In the drive circuit shown in Fig. 1, in order to rotate at an extremely low speed, when the motor speed control voltage Vs becomes extremely small (near zero volts), the emitter-base voltage of the PNP transistor T1 is
There was a problem that this transistor would not turn on and the motor would not drive. That is, motor speed control voltage Vs
When T1 becomes less than the base-emitter voltage of transistor T1, this transistor will not turn on and no drive current will flow to the coil. Therefore Vs−
The relationship between the rotational speeds was not linear, and a nonlinear characteristic occurred where the rotational speed was zero in the area where Vs was 1V or less.

The present invention has been made in view of the above-mentioned problems, and is designed to allow the drive circuit to operate even when the speed control voltage is small.

The present invention provides a brushless motor drive circuit that sequentially turns on and off a multi-phase switching transistor whose emitter is coupled to a motor drive coil and whose collector is supplied with a motor speed control voltage, in accordance with the rotational position of the rotor. A means is provided for forming a voltage higher than the speed control voltage by the base-emitter voltage of the transistor based on the speed control voltage, and supplying this voltage to the base of the switching transistor.

Even when the motor speed control voltage supplied to the collector of the switching transistor becomes less than the base-emitter voltage of the transistor, a voltage higher than this speed control voltage by the base-emitter voltage is applied to the base of the switching transistor. The switching transistor can be operated in saturation to apply a motor speed control voltage to the motor drive coil at its emitter. As a result, the motor can be driven even when the motor speed voltage is very low, close to zero volts.
Ultra-low speed rotation can be obtained. The characteristic graph of motor speed control voltage versus rotation speed has a linear relationship that extends from Vs≈0 in a straight line.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a circuit diagram of a motor drive circuit (for one phase) showing an embodiment of the present invention. In the drive circuit of this embodiment, the drive transistors T1 and T2 are
NPN type is used. A speed control voltage Vs is supplied to the collector of T1. The respective transistors are driven by Darlene-connected transistors T13, T14 and T15, T16. The first stage transistors T13 and T15 of each Darlington circuit are driven by PNP type gate transistors T17 and T18. These transistors T17 and T18 are
A current switching signal formed in a switching signal forming circuit (not shown) is also turned on and off at a predetermined timing. For example, T17 is 0 in electrical angle
It is on in the range from 180° to 60°, and T18 is on in the range from 180° to 240°.

When the gate transistors T17 and T18 are turned on, the base current I _B supplied from the transistor T19 flows through the Darlington circuit T1.
3, flows into T14 and T15, T16. Base current I _B supplied from transistor T17
is controlled so that the voltage Vo at the connection point b between the drive transistors T1 and T2 (ie, the voltage supplied to the coil 1A) is always equal to the speed control voltage Vs. That is, the minimum current I _B is generated to bring the transistor T1 into saturation so that its collector-emitter saturation voltage becomes approximately zero. The current I _B flowing through transistor T19 is controlled by a transistor T20 connected to its base, T20 being connected to the Darlington transistor T13.
The voltage Va at the emitter (point a) of the diode D1
It is also driven by the detection voltage detected by .

These diode D1, transistor T1
9 and T20 form a voltage higher than this voltage by the base-emitter voltage of the switching transistors (transistors T1 and T14 in this embodiment) based on the motor speed control voltage Vs, and this voltage is applied to the switching transistors. It constitutes circuit means for supplying the base.

A bias resistor R1 is coupled between the collector and base of the transistor T19, and the power supply voltage Vcc is supplied to the collector through a current limiting circuit consisting of transistors T21, T22 and resistors R2, R3. Since the resistor R2 supplies operating current (base current of T1 and T2) to the Darlington circuits T13, T14 and T15, T16, if the current flowing through R2 becomes excessive,
T22 is turned on and T21 is turned off.

In Figure 2, the potential at point a with reference to point b is Va = Vo + V _BE (T1) + V _BE (T14) ... (1) (where V _BE is the base of each transistor -
emitter voltage). Furthermore, the potential at point a with respect to Vs is Va=Vs+V _BE (T20)+V _F (D1) (2) (where, V _F is the forward voltage of the diode).
Here, if V _BE ≈V _F and the V _BE of each transistor is approximately equal, then from equations 1 and 2, Vs=Vo (3). That is, when the third equation is established, the control loops D1, T20, T19, T17, T in FIG.
13 is in equilibrium. In this state, the potential Vo at point b is equal to the speed control voltage Vs, and the collector-emitter voltage of the transistor T1 is approximately zero.

The base current of transistor T1 is insufficient, and T1
When a voltage is generated between the collector and emitter of , Vo<Vs, and therefore, as Vo decreases, the voltage at point a also decreases (Equation 1). Therefore, the base current of transistor T20 also decreases,
The current through R1 decreases and the base voltage of T19 increases. As a result, the emitter current of T19 increases, and this current becomes the base current I _B of T19.
17 to the transistor T13, the base current of the drive transistor T1 increases. This controls the collector-emitter saturation voltage of T1 to approximately zero volts.

In this way, even if the speed control voltage Vs changes, the minimum base current necessary to saturate T1 is supplied to T1 accordingly. Even if Vs is extremely small and becomes 1V or less, the condition of the third equation can be satisfied, and the motor can be rotated at an extremely low speed.

When the other drive transistor T2 of the A phase is turned on and current flows in the opposite direction to the coil 1A, the Vs side transistor (corresponding to T1) of the other phase (B or C) is turned on, so Transistor T20 is driven in accordance with the detection output of detection diode D2 of the other phase, thereby controlling the emitter current of transistor T19. Therefore, when the transistor T18 is turned on, a collector current that is substantially the same as the on-state current of the transistor T17 described above flows, and this current flows into the base of the transistor T15 as a base current I _B. Therefore, transistors T13, T14 and T1,
If the transistors T15, T16, and T2 are configured with the same specifications, the emitter current of the transistor T15 is the same as the potential of the emitter (point a) of the transistor T13 (during operation) and Va. Va
is determined by the second equation, so the next stage transistor T1
The emitter (point c) potential Vc of No. 6 is as follows: Vc = Va - V _BE (T16) = Vs + V _BE (4).

Therefore, the base current proportional to Vs flows through the resistor R4.
is supplied to T2 via , and T2 is turned on. R
The resistance value of 4 is the impedance T2 of the coil 1A.
If the value is set smaller than the value divided by the DC amplification factor, T2 will always be turned on in a fully saturated state. Also
Even when Vs becomes extremely small, as is clear from the fourth equation, sufficient base voltage is supplied to turn on T2.

In this way, according to the drive circuit shown in Fig. 2, as shown in the graph of Vs-N (rotation speed) in Fig. 3, it is possible to control the rotation speed from a value of Vs of zero, and the rotation speed can be controlled to exceed the value of the motor. It is possible to rotate at low speed. Note that Vs is formed from the power supply voltage Vcc, so
Always Vs<Vcc.

FIG. 4 shows a specific example of the motor drive circuit of this embodiment. In FIG. 4, a position detection signal corresponding to the rotation angle of the rotor is obtained from the A-phase Hall element 2. In addition, Hall elements of other phases (not shown)
is provided at an interval of 120 degrees in electrical angle from the A-phase Hall element 2. The output of the Hall element 2 is supplied to the differential amplifier 3, and the output is 180 degrees in electrical angle.
A switch signal is formed which alternately goes high and low in degrees. This switch signal is applied to current amplification transistors T23, T24, T25, T2.
6 to the bases of transistors T27 and T28. The output of T27 is a diode T
30 to the transistor T32, while the output of T28 is supplied to the transistor T32 in reverse phase via the inverter T29 and the diode T31.
32.

The transistors T27 and T29 are selectively operated by the output of the forward/reverse control circuit 4. That is, when the control signal K supplied to the transistor T33 of the forward/reverse control circuit 4 is at a high level, the transistor T34 is turned on and the transistor T27 is operated, so that T32 is in positive phase.
It is turned on and off in 180° increments. Further, when the control signal K is at a low level, the transistor T33 of the forward/reverse control circuit 4 is turned off, the transistor T35 is turned off, and the transistor T34 is turned on, and the transistor T29 is operated, thereby causing the transistor T32 to turn off.
is turned on and off in reverse phase in 180° increments. This controls forward and reverse rotation of the motor.

The output a of the transistor T32 and the base input in phase opposite thereto are connected to the transistors T37 and T32, respectively.
Through 38 a control transistor T similar to that in FIG.
17 and T18. Note that transistors T39 and T40 are provided at the bases of transistors T37 and T38, respectively, and are turned on and off by switching signals of other phases.
0 that overlaps with the other phase of the positive phase and negative phase switching signals a with an interval of 180°.
The transistors T37 and T38 are configured to be turned on in the ranges of ~60° and 180° to 240°, respectively. Note that the switching signal a is also supplied to the B-phase and C-phase drive circuits 5 and 6, and combined with the B-phase and C-phase switching signals,
A drive signal for each coil is formed.

The A-phase drive circuit of FIG. 4 operates in the same manner as that of FIG. Note that since the current limiting circuits T21 and T22 and the base current control transistors T19 and T20 are used in common for each phase, the emitter of T19 and the base of T22 are also connected to the B phase and C phase.

Next, FIG. 5 shows a motor drive circuit (A phase) of a second embodiment of the present invention. In this example, four series diodes D2 to D5 are used at point d (T1
9) forms the voltage Vd. Using Vs as a reference, Vd is Vd=Vs+4V _F (5) (V _F is the forward voltage of the diode). this voltage
Even at Vd, the emitter current of transistor T19 is determined, and from T19 to gate transistor T1
A base current I _B is supplied to the Darlington transistor T13 via the transistor T13. In this case, diodes D2-D5 and transistor T19 form a voltage based on the motor speed control voltage Vs that is higher than this voltage by the base-emitter voltage of the switching transistors (transistors T1, T14, T13 in this example). and constitutes circuit means for supplying this to the base of the switching transistor. Emitter of transistor T1 (b
The potential Vo at point ) is Vo = Vd - V _BE (T19) - V _BE (T13) - V _BE (T14) - V _BE (T1) ...(6), so Vd of Equation 5 is added to Equation 6. , and V _F ≒V
If _BE , then Vo=Vs...(7). That is, as in Fig. 2, the base current control circuit operates so as to satisfy Equation 7, and as a result, even if Vs fluctuates, the base current I _B is determined so that T1 is always turned on in a saturated state. . Further, the emitter potential Vc of the transistor T16 also becomes Vc=Vd-3V _BE =Vs+V _BE (8), and a base voltage that can turn on T2 is ensured no matter what state of Vs. As a result, as in FIG. 2, the drive circuit operates even when Vs is near zero, allowing the motor to rotate at an extremely low speed.

As mentioned above, the present invention is based on the motor speed control voltage, and the base voltage of the transistor is lower than this voltage.
A voltage higher than the emitter voltage is generated and supplied to the base of a switching transistor whose emitter is connected to a motor drive coil.
Therefore, even when the motor speed control voltage is extremely low (for example, 0.7 V or less), the switching transistor can be sufficiently saturated and turned on, and therefore the motor can be driven at an extremely low speed.

[Brief explanation of the drawing]

FIG. 1 shows a drive circuit conventionally used for a three-phase bidirectional brushless motor, and FIG. 2 shows a drive circuit for one phase of a three-phase bidirectional brushless motor showing a first embodiment of the present invention. FIG. 3 is a graph showing the motor speed control voltage-rotation speed characteristic by the drive circuit of FIG. 2, FIG. 4 is a circuit diagram showing a specific example of a motor drive circuit using the drive circuit of FIG. 2,
FIG. 5 shows a motor drive circuit (for one phase) showing a second embodiment of the present invention. In addition, in the symbols used in the drawings, 1
A, 1B, 1C... Coil, 2... Hall element,
5... B phase drive circuit, 6... C phase drive circuit.

Claims (1)

[Claims] 1 A multi-phase switching transistor whose emitter is coupled to a motor drive coil and whose collector is supplied with a motor speed control voltage, and a voltage higher than this voltage by the base-emitter voltage of the transistor, based on the motor speed control voltage. A brushless motor drive circuit comprising means for supplying the switching transistor to the base of the switching transistor, and means for sequentially turning on and off the switching transistor in accordance with the rotational position of the rotor.