JPS6326638B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a brushless motor which is configured to detect the rotational position of a rotor and sequentially conduct the drive transistors connected in series with the phase windings to connect the rotation of the rotor. Protective measures are provided to prevent the motor, and more specifically, to prevent overcurrent from simultaneously flowing through multiple phases over a long period of time and causing an excessive temperature rise in the drive transistor or phase windings, which may lead to failure or destruction of the device. Regarding the equipped brushless motor, extremely stable and reliable operation is guaranteed with a small number of external parts, especially when the drive circuit part is integrated into an IC.

Here, the necessity of this type of protection means will be explained using a three-phase brushless motor as an example. First, in electrical angle, facing the rotor magnet.
Based on the information from the rotational position detector of the rotor magnet, the first
When the current is applied sequentially as shown in the figure (in Fig. 1, Ia, Ib, and Ic indicate the current flowing to the A phase, B phase, and C phase, respectively, and θ _e indicates the electrical angle of rotation. ), the rotor magnet rotates in one direction, but in reality, if a sudden current switch as shown in Figure 1 is performed, a large surge voltage may occur in the stator winding, or the switching point between the two phases may occur. Since the dead point where the rotor does not start occurs due to the deviation of the rotor, as shown in Fig. 2, the currents of the two phases are made to overlap near the switching point, and the current is gradually increased in the overlapped part. It is common to reduce it.

When the rotor magnet is rotating, the overlap part (hatched part in Figure 2),
Since the other portions appear alternately and the period of the overlap portion is short, no harm will occur due to the provision of the overlap portion. However, if the rotor magnet is prevented from rotating near the center of the overlap part by some external force when the motor is started, a larger current will simultaneously flow through the two-phase stator windings than during normal rotation. As a result, the amount of heat generated in the stator windings (phase windings) increases, causing an abnormal temperature rise inside the motor, or the drive transistors that supply electricity to the stator windings are integrated into a single IC. When integrated, there is a problem in that the temperature of the IC increases abnormally, eventually leading to the IC's destruction.

A method to prevent this phenomenon is to detect that current continues to flow simultaneously in two phases for a long period of time, and use this detection signal to cut off the current using the set output of a bistable circuit such as an RS flip-flop circuit. Various configurations are possible, but in this case, a first time constant circuit is used to detect that current has flowed for a long time, and a second time constant circuit is used to initially reset the bistable circuit when the power is turned on. Since a time constant circuit is required, there are disadvantages such as a complicated circuit configuration and the need for at least two capacitors.

The present invention can solve the above-mentioned problems, and its greatest feature is that it includes a bistable means that is less likely to malfunction due to external noise when the circuit is implemented as an IC.

FIG. 3 is a circuit diagram of one embodiment of the present invention. In the figure, the outputs of Hall effect elements 1, 2, and 3 for detecting the rotational position of a rotor magnet (not shown) are connected to transistors 4 to 3, respectively.
26, 4 between the input terminals of the distribution circuit 100 configured by diodes 27 to 29, and resistors 30 to 44
applied to a-5a, 6a-7a, 8a-9a,
Output transistors 24, 2 of the distribution circuit 100
The collectors of transistors 5 and 26 are connected to the bases of detection transistors 45, 46, and 47, respectively, as well as the predrive transistors 48 and 47 of each phase.
It is also connected to the bases of 49 and 50.

The emitters of the transistors 48, 49, 50 are respectively drive transistors 51, 52,
53 and is connected to the base of resistor 5
4, 55, and 56 to the negative side feed line (indicated by the ground symbol), and the collectors thereof are connected in common, and are also connected to the positive side feed line (+V _cc ) via a resistor 57. transistor 5
Emitters 1, 52, and 53 are all connected to the negative feed line, and stator windings AA, BB, and BB are connected between the collector and the positive feed line, respectively.
CC is connected.

The collector of the output transistor 61 of the two-phase energization detection circuit 200 constituted by the detection transistors 45, 46, 47, transistors 58-61, and resistors 62-67 is connected to the transistor 62.
70, a diode 71, and resistors 72 to 75.
The common collectors of the zero output transistors 64 and 66 are connected to the base of a transistor 77 via a resistor 76 and to the base of a transistor 79 via a resistor 78.

Further, the collector of the transistor 77 is connected to the reset release terminal 71a, the emitter of the transistor 77 is connected to the collector of the transistor 80, the emitter of the transistor 80 is connected to the negative power supply line, and the base of the transistor 77 is connected to the resistor 81 and the diode 82. is connected to the disable terminal DS through. The collector of the transistor 79 is connected to the base of a transistor 83, and is also connected to the disable terminal DS via a resistor 84 and the diode 82, and the emitter of the transistor 83 is connected to the negative power supply line. connected to the base and collector of transistor 85 and further to the base of transistor 86 via current control means 400;
The common emitters of the transistors 85 and 86 are connected to a constant voltage supply line.
6 is connected to the command current input terminal 10a of the distribution circuit 100.

Further, a pull-up resistor 87 is connected between the disable terminal DS and the constant voltage supply line, and a collector-emitter of a transistor 88 is connected between the positive side supply line and the constant voltage supply line. The base of the transistor 88 is connected to the midpoint of a series circuit of a resistor 89 and a constant voltage diode 90 connected between power supply lines.

In FIG. 3, a resistor 76 and a transistor 77 constitute a holding circuit 500 that holds the monostable circuit 300 in a reset release state by the output signal of the monostable circuit 300.
and a transistor 79 which is a cut-off circuit that cuts off the supply of energization command signals for each phase generated by the control means 400 and the distribution circuit 100 to the drive transistors 51, 52, and 53 in response to the output signal of the monostable circuit 300. A circuit 600 is configured, and the plus side feed line is connected to the plus side feed terminal DC.

Now, in FIG. 3, transistors 45 to 5
The knee voltage between the base and emitter of transistors 3 and 3 is all equal, and its value is V _BE , and the emitter resistance of each transistor is also sufficiently small, and the DC current amplification factor is
h _FE should be large enough, and the resistance should be 62 to 6
4 and 97 are all equal, and if the resistance value of the resistor 65 is r and the resistance value of the resistor 66 is 1.5r, then the A-phase stator winding AA and the B-phase stator winding
When only one phase of the stator windings CC of the BB and C phases is energized, the transistors 58 to 6
0, the current I _p1 drawn from the Wilson constant current circuit constituted by the resistors 65 and 66 to the detection transistors 45 to 47 has a value given by the following equation.

I _p1 = V _BE /R...(1) On the other hand, the resistor 67 is connected to the Wilson constant current circuit.
Since the current I _s1 flowing out to is 1.5I _s = I _p ,
The following formula is obtained.

I _s1 = 2V _BE /3R ... (2) In this case, the voltage drop V _R1 at the resistor 67 is V _R1 = I _s · R = 2V _BE /3 ... (3) and the transistor 61 has a base current does not flow.

When two phases of the three-phase stator winding are energized simultaneously, the current I _p2 drawn from the Wilson constant current circuit to the detection transistors 45 to 47 is I _p2 = 2V _BE /R... (4) becomes. Similarly, I _s2 becomes I _s2 =4V _BE /3R (5). Therefore, the base current I _b2 of the output transistor 61 is I _b2 = I _s2 - V _BE /R = V _BE /3R (6). At this time, by setting the resistance value R 72 of the resistor ₇₂ sufficiently large, the transistor 6
1 can be saturated.

Incidentally, if the DC current amplification factor of the transistor 61 is h _FE1 and the voltage of the constant voltage feed line is V _R , then the resistance value R ₇₂ of the resistor 72 is R ₇₂ > 3R・V _R /h _FE1・V _BE ... (7) For example, h _FE1 = 30, V _BE = 0.7V,
When V _R =7V, R ₇₂ >R...(7)'.

On the other hand, the internal configuration of the monostable circuit 300 is as follows:
A comparison input terminal 63a of a comparator constituted by transistors 63 to 70 and a resistor 75 is connected to the hot side terminal of a capacitor 76 which is charged and discharged by the switching transistor 62, and the reference voltage input of the comparator is terminal 64
a is connected to a constant voltage feed line.

Normally, the switching transistor 62 is in the on state and the collector voltage of the transistor 66 is approximately zero, but when the switching transistor 62 is turned off by the transistor 61, the voltage from the resistor 74 is reduced. The potential of the capacitor 76 gradually rises as a result of energization, and when the charging voltage V _c exceeds the regulated power supply voltage _VR , the comparator operates and the collector potential of the transistor 66 rises.

When the switching transistor 62 turns off, that is, when the free-running monostable circuit 300
The time period from when the reset of the transistor 66 is released until the collector potential of the transistor 66 rises is
If T _p is the resistance value of the resistor 74, R ₄ is the capacitance of the capacitor 76, and C ₆ is the power supply applied to the positive feed line DC, then V _cc is the power supply applied to the positive feed line DC. becomes. Therefore, T _p is expressed by the following equation.

T _p = −C ₆ · R _{4 lo} (1−V _R /V _cc ) …(9) Here, for example, V _cc = 9V, R ₄ = 100KΩ, C ₆ =
Assuming 6.8μF, T _p = -6.8×10 ^-6 ×100×10 ³ ×e _o (2/9) ≈1.03 (sec), and if the reset release signal is continuously applied for more than 1 second, the transistor 66 Collector potential increases.

When the collector potential of the transistor 66 rises, both the transistor 77 and the transistor 79 are turned on, and the transistor 83 is turned off, cutting off current to each phase, and the reset release signal input terminal 71a is turned on. The potential of is continuously held at approximately zero.

Note that at this time, when the potential of the disable terminal DS is forced to zero by an external disable signal, the transistor 80 is turned off, so the transistor 62 is turned on again, and the capacitor 76 is turned off. The charge is discharged and the free-running monostable circuit 300 is reset.

By the way, when the rotor magnet of the brushless motor is rotating, overlapping periods and non-overlapping periods shown by the shaded area in FIG. By keeping the output transistor 61 in the 2-phase conduction detection circuit 200, even if the output transistor 61 of the two-phase conduction detection circuit 200 generates a reset release signal, the output transistor 61 will be able to reset the reset signal again by the time the free-running monostable circuit 300 generates an output. Monostable circuit 300 is reset and cutoff circuit 600 does not operate.

However, if the rotor magnet of the brushless motor is stopped rotating at the overlap portion for a long time, the output transistor 6
1 continuously generates a reset release signal, the monostable circuit 300 generates an output signal, and the current supply to each phase is cut off.

When the power supply to each phase is cut off, the output transistor 61 shifts to the off state, but instead, the holding circuit 500 operates before that to keep the switching transistor 62 in the off state.

The monostable circuit 300 and the holding circuit 500 can be considered to form a type of bistable circuit, but the difference from a general bistable circuit is that the motor rotor is rotating or stopped. Delay element (time constant circuit) to determine whether
Because it is included in the positive feedback loop for bistable operation, the overall configuration is simple, and the delay element works effectively against external noise such as surges, making it extremely resistant to noise. There is an advantage that the device can be realized.

Furthermore, since the bistable circuit consisting of the monostable circuit 300 and the holding circuit 500 is always reset by the delay element when the power is turned on, the power supply terminal
When the DC potential rises slowly, the switching transistor 62 turns on earlier than the transistor 61 turns on (the switching transistor 62 turns on before the voltage across the resistor 67 reaches V _BE ). 62 reaches _VBE ), so no initial reset element is needed for the bistable circuit.

Although FIG. 3 shows an example of the circuit configuration of a three-phase brushless motor, the present invention is applicable to any brushless motor that has multiple phase windings and multiple drive transistors, not just three-phase motors. Needless to say.

Further, although the control means 400 is shown by a variable resistor symbol, generally a speed control circuit for detecting the rotational speed of the rotor and controlling the speed at a constant speed is often used.

Furthermore, the resistor 74 that determines the metastable time of the monostable circuit 300 may be any other current supply means such as a constant current circuit, and the drive transistors 51, 5
2, 53, etc. are not limited to bipolar transistors, but power FETs are one example.
It is also possible to use unipolar transistors such as

In this way, in the brushless motor of the present invention, in order to sequentially energize the plurality of phase windings AA, BB, and CC, the output electrode (collector or emitter for bipolar transistors, drain or source for unipolar transistors) is used as the output electrode. ) are connected to one end of each phase winding.
Then, an energization command is given to the input electrodes of the plurality of drive transistors (the input electrode is the base for bipolar transistors, and the gate for unipolar transistors) according to the output signals of rotor rotational position detectors 1, 2, and 3. A distribution circuit 100 that distributes signals, a two-phase energization detection circuit 200 that detects that the energization command signal is simultaneously supplied to a plurality of drive transistors, and a reset state is determined by the output signal of the two-phase energization detection circuit. A free-running monostable circuit 300 that generates an output signal after a certain period of time has elapsed from the reset release point, and a holding circuit 50 that holds the monostable circuit in the reset release state using the output signal of the monostable circuit.
0, and a cutoff circuit 600 that cuts off the supply of the energization command signal to the drive transistor by the output signal of the monostable circuit, wherein the monostable circuit and the holding circuit are connected to each other. Since there is a delay element in the positive feedback loop of the bistable means constructed in this way, overcurrent protection can be achieved with a simple circuit configuration, strong against external noise, and requiring no special initial reset means. This mechanism can be realized and has great effects.

[Brief explanation of the drawing]

Figures 1 and 2 are current waveform diagrams of a three-phase brushless motor to explain the problems of the prior art;
FIG. 3 is a wiring diagram of a drive circuit in one embodiment of the present invention. 51, 52, 53...drive transistor,
AA, BB, CC...Stator winding, 100...Distribution circuit, 200...2-phase current detection circuit, 300...
Monostable circuit, 500...holding circuit, 600...breaking circuit.

Claims (1)

[Claims] 1. A plurality of drive transistors whose output electrodes are connected to one end of each phase winding in order to sequentially energize the plurality of phase windings, and an output signal of a rotor rotational position detector. a distribution circuit that distributes an energization command signal to the input electrodes of the plurality of drive transistors according to the energization command signal; a two-phase energization detection circuit that detects that the energization command signal is simultaneously supplied to the plurality of drive transistors; and a bistable operation. a free-running monostable circuit that includes a time constant circuit in a positive feedback loop for generating an output signal after a predetermined period of time has elapsed from the time of reset release by the output signal of the two-phase energization detection circuit;
a holding circuit that holds the monostable circuit in a reset release state by an output signal of the monostable circuit; and a cutoff circuit that cuts off the supply of the energization command signal to the drive transistor by the output signal of the monostable circuit. A brushless motor equipped with a circuit. 2. In the description of claim 1, the monostable circuit includes a switching transistor to which an output signal of the two-phase energization detection circuit is applied to an input electrode, and a switching transistor and another energization means. Therefore, the capacitor is configured to include a capacitor that is charged and discharged, and a comparator that compares the charging voltage of the capacitor with a reference voltage and generates an output signal when the charging voltage exceeds the reference voltage. Features a brushless motor.