JPH0526438B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a brushless motor drive circuit that detects the position of a rotor based on the induced voltage of a drive coil.

BACKGROUND TECHNOLOGY AND PROBLEMS In brushless DC motors used in equipment such as VTRs and tape recorders, for example, in the case of a motor with a three-phase stator coil (i.e., drive coil), the rotor rotates 120 degrees in electrical angle. The current is made to flow through each phase sequentially each time. For this purpose, conventional brushless motors are provided with a position detector that detects the position of the rotor. In a brushless motor, the phase of the rotor and current switching timing are matched to generate the optimum torque, so three of the above position detectors are used, and they are arranged at 120° electrical angle intervals. I try to do that. However, with the miniaturization of devices in recent years, motors have also become smaller, and as a result, there is no longer enough space for arranging circuit components and the like connected to the motors. Hall elements are widely used as the position detector, but it is becoming difficult to have enough space to arrange three Hall elements. Further, although 8 to 12 lead wires are connected to a detector using a Hall element, there is insufficient space for the wiring. Furthermore, the power consumption of a detector using a Hall element is so large that it cannot be ignored from the viewpoint of power saving.

Therefore, the present applicant filed Japanese Patent Application No. 57-54871.
The present invention provides a brush motor in which the position detector described above is omitted, and instead, the stator coil is energized and the induced voltage induced in the coil is used as a rotor position detection signal.

FIG. 1 and FIG. 2 show an embodiment of the invention according to the above application.

FIG. 1 shows the relationship among the induced voltage, energization time, and torque of each phase coil in a steady state of a brushless motor having three-phase coils of U-phase, V-phase, and W-phase.

Sin wave induced voltages generated in each phase E _U , E _V , E _W
occur sequentially with a shift of 2/3π as shown in FIG. 1A. That is, E _U = sinθ ... E _V = sinθ (θ-2/3π) ... E _W = sinθ (θ-4/3π) ... In addition, the energization times T _U , T _V , T _W of each phase are as follows: As shown in FIG. 5B, each corresponds to a range in which the corresponding induced voltage is at a level of 1/2 or less of the peak value on the negative side of the reference potential V _S. This range is 120° of rotor
corresponds to the electrical angle of Assuming that _the motor is energized in the order of U phase → V phase → W _phase , _the induced voltage _{V 2 of} the phase at the starting point of energization and the The induced voltage of the phase energized V ₁
is always in the relationship of V ₁ :V ₂ =2:-1.

Therefore _, the energization time T _U starts from time t ₁ when E _{V / 2} + _{E U} ≦V _S . Also, the energizing time
T _V starts from time t ₂ when the above formula begins to hold true and continues until time t ₃ when E _U /2+E _W ≦V _S . . . begins to hold true. Further, the energization time T _W starts from time t ₃ when the above formula starts to hold true, and continues until time t ₄ when the above formula starts to hold true again.

Therefore, in the motor drive circuit, E _U ,
What is necessary is to detect _EV and _EW and set T _U , _TV and _TW within a range where each voltage satisfies the above formula. Incidentally, the thick line curve in FIG. 1C shows the output torque in a steady state.

FIG. 2 shows an embodiment of a motor drive circuit to which the above-described principle is applied. It is assumed that the rightmost point in Figure 2 is connected to the leftmost point.

In the figure, the coils 1 _U , 1 _V , 1 _W of each phase are sequentially supplied with current from the power supply terminal 2 of the reference voltage _VS by turning on the transistors Q ₁ , Q ₂ , Q ₃ respectively. is energized. Due to this energization, induced voltages _EU , _EV , and _EW appear at one end of each coil. The above Q ₁ , Q ₂ , and Q ₃ are turned on when the outputs of the comparators 3 _U , 3 _V , and 3 _W connected to their bases are "H" (high level). The negative terminals of these comparators 3 _U , 3 _V , 3 _W are connected to the induced voltage detection point, and the positive terminals are connected to the transistor
They are connected to the collectors of Q ₄ , Q ₅ , and Q ₆ , respectively.
Q ₄ is controlled on and off via Q ₇ by turning on and off Q ₂ , and Q ₅ is controlled on and off by turning Q ₃ on and off.
It is controlled on and off via _Q8 , and _Q6 is controlled on and off via _Q9 by the on and off of _Q1 .

One end of each coil 1 _U , 1 _V , 1 _W is connected to each other via induced voltage detection resistors R ₁ , R ₂ ,
The connection point between R ₁ and R ₂ is the detection point. The resistance values of R ₁ and R ₂ are selected to be R ₁ :R ₂ =2:1. Therefore, 1/2E _V +E _U is detected at the detection point, 1/2E _W +E _V is detected at the detection point, and 1/2E _U +E _W is detected at the detection point.

Next, the operation of the above configuration will be explained.

At time _t1 in FIG. 1, it is assumed that, for example, the output of comparator _3U is "H", _Q1 is turned on, and coil _1U is energized. At this time, Q ₂ is off,
Q ₇ is on and Q ₄ is off. Therefore, the positive terminal of the comparator 3 _U is approximately V _S. Also, the voltage at the detection point is lower than V _S. As a result, the output of this comparator _3U becomes "H". Also, Q ₃ is off, Q ₈ is on, and Q ₅ is off. Therefore, the positive terminal of comparator 3 _V is omitted.
It is _VS. Further, the voltage at the detection point is higher than V _S. As a result, the output of this comparator 3 _V becomes "L" [low level (approximately ground potential)].
_Q2 is turned off. Also, when Q ₁ is turned on, Q ₉ is turned off and Q ₆ is turned on. Therefore, the positive terminal of the comparator _3W is set to "L". Further, the voltage at the detection point is higher than V _S. As a result, the output of this comparator 3 _W becomes "L" and Q ₃
is turned off.

In this state, when the rotor rotates 120° and reaches time _t2 , the voltage at the detection point drops to V _S and further increases to V _S
The output of comparator 3 _V changes from "L" to "H" because it starts to become lower than . This turns on Q ₂ and starts energizing the coil 1 _V.
Q ₇ is off and Q ₄ is on. Therefore, comparator 3 _U
The positive terminal of becomes "L". At this time, since the voltage at the detection point is higher than the ground potential, the output of the comparator 3 _U changes from "H" to "L". Therefore, Q ₁ is turned off and the current to coil 1 _U is cut off. Furthermore, when Q ₁ is turned off, Q ₉ is turned on and Q ₆ is turned off.
Therefore, the positive terminal of the comparator 3 _W becomes approximately V _S .
At this time, since the voltage at the detection point is higher than V _S , the output of this comparator 3 _W remains "L". This keeps Q ₃ off and energization of coil 1 _W is prohibited.

Next, at time _t3 , the state of the circuit in each phase is transferred to the adjacent phase, and a similar operation is performed. As a result,
The W phase is energized and the V phase is deenergized,
The off state of the U phase is maintained. Then, at time t ₄ , the process returns to the initial state, and the same operation is repeated thereafter.
Through this series of operations, the above equations are sequentially satisfied, and the energization times T _U , _TV , and _TW of each phase are sequentially set.

Therefore _, in the _drive circuit shown in _FIG .
These coils 1 _U , 1 _V , 1 _W in the drive circuit shown in the figure
Connected with lead wires to circuit parts other than For this reason, an equivalent resistance R ₀ as shown by the dotted line is connected between the neutral point to which one ends of the coils 1 _U , 1 _V and 1 _W are commonly connected and the power supply terminal 2. The existence of this equivalent resistance R ₀ and the above reference voltage V _S
Because the output impedance of the reference power supply that supplies the voltage is low, noise may be added to the coils 1 _U , 1 _V , and 1 _W when switching transistors Q ₁ , Q ₂ , Q ₃ , etc. If such noise occurs when the motor is started, the level of the induced voltages _EU , _EV , and _EW is low at startup, so the level of the noise becomes relatively high. Relatively high-level noise is mixed into the voltage at the detection point obtained by combining the voltages _EU , _EV , and _EW . On the other hand, since the reference voltage V _S is constant, the relationship between the reference voltage V _S and the voltage at the detection point is less likely to be reversed due to the above noise than in the case without such noise. be.

Therefore, the comparators 3 _U , 3 _V , and 3 _W output "L" when they should output "H", and conversely output "H" when they should output "L". As a result, the timing of energization switching will not be as shown in FIG. 1 because malfunctions will occur. For this reason, energization is performed regardless of the induced voltage, which may cause the energization order to be out of order, causing oscillation.

OBJECTS OF THE INVENTION The present invention provides a brushless motor drive circuit that prevents malfunctions caused by the above-mentioned equivalent resistance R ₀ .

Embodiment FIG. 3 shows an embodiment of the present invention, in which the same parts as in FIG. 2 are given the same reference numerals.

In the figure, the induced voltage of coils 1 _U , 1 _V , 1 _W
EU , _EV , _EW are added to transistors _Q10 , _Q11 , _Q12 and the base. These Q ₁₀ , Q ₁₁ , and Q ₁₂ are connected in parallel between the power supply terminal 2 and a current source 4 that flows a constant current I ₁ , and a series circuit of a transistor Q ₁₃ and a resistor R ₃ is further connected in parallel. Ru. The collector and base of _Q13 are connected to make it equivalent to a diode, and the voltage _V1 obtained at the connection point is applied to the positive terminals of the comparators _3U , _3V , and _3W .

According to the above configuration, when the motor is started, the drive circuit shown in FIG. 3 operates as follows.

In other words, the induced voltages E _U , E _V , E _W are the reference voltage V _S
When it is sufficiently small, there is a constant current I ₁ , so for transistors Q ₁₀ , Q ₁₁ , and Q ₁₂ ,
The operation of any one transistor to which the highest voltage is applied among E _U , _EV , and _EW becomes dominant,
The current values of other transistors are significantly reduced.
Therefore, the anode voltage V ₁ of the diode formed between the base and emitter of transistor Q ₁₃ is
The emitter voltages of Q ₁₀ , Q ₁₁ , and Q ₁₂ are higher by V _BE , and the highest voltages among _EU , _EV , and _EW are almost equal.

On the other hand, as is clear from Fig. 3, the total current value of the three transistors Q ₁₀ , Q ₁₁ , Q ₁₂ and the diode formed between the base and emitter of Q ₁₃ is the constant current I ₁ Match. Then, the transistor to which the highest voltage above is applied is
Assume that Q ₁₁ and that the induced _{voltage EV} has increased due to noise mixed into it. At this time,
The current value of Q ₁₁ increases, and the current value of Q ₁₃ decreases by the amount of increase. Therefore, the voltage drop due to the resistor R ₃ also becomes smaller, so the voltage V ₁ increases. Therefore, even if the voltage at the negative terminals of the comparators 3 _U , 3 _V , and 3 _W increases due to the above noise, this increase will be caused by
This is offset by the voltage increase of V ₁ mentioned above. Also,
When the induced voltage _EV decreases due to the noise, the operation is completely opposite to that in the above case, so the influence of the noise is canceled out as well.

In this way, the aforementioned malfunctions of the comparators 3 _U , 3 _V , and 3 _W can be prevented. Furthermore, after the motor is started, the induced voltages _EU , _EV , and _EW rise and the emitter voltages of _Q10 , _Q11 , and _Q12 become high, so _Q13 is cut off and the above voltage _V1 becomes the reference voltage. Voltage
Clamped to V _S. Therefore, after the voltage level of V ₁ is clamped to V _S , the circuit shown in FIG. 3 becomes substantially equivalent to the circuit shown in FIG. 2.

Effects of the Invention Malfunctions due to voltage drop of equivalent resistance between the drive circuit and the motor can be prevented. Therefore, even if there are differences in motor coil impedance, drive voltage, line impedance between the drive circuit and the motor, etc., stable operation is possible without adjustment.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the induced voltage, energization time, and output torque of the brushless motor proposed in the earlier invention, Figure 2 is a circuit diagram showing an embodiment of the earlier invention, and Figure 3 is an implementation of the present invention. FIG. 2 is a circuit diagram showing an example. In addition, in the symbols used in the drawings, 1 _U , 1 _V ,
1 _W ...Stator coil, 3 _U , 3 _V , _{3 W} ...Comparator, Q ₁ , Q ₂ , Q ₃ ... Transistor, E _U , EV, E _W
...Induced voltage, V _S ...Reference voltage.

Claims (1)

[Claims] 1 The induced voltages induced in multiple phases are combined in a predetermined relationship, this combined voltage is compared with a reference voltage, and the drive coils of each phase are sequentially energized based on the comparison result. , when starting the motor, the maximum voltage among the induced voltages of each phase is used as the reference voltage, and in a region where the induced voltage is sufficiently large, the common power supply voltage of each phase is used as the reference voltage. Features a brushless motor drive circuit.