JPH0474957B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is applicable to tape recorders, record players,
This invention relates to a brushless motor that can be used in video tape recorders and the like.

Conventional configuration and its problems Brushless motors, in which armature current is switched by transistors and generated torque is controlled by command input, are widely used in the above-mentioned industrial fields. A conventional example of a typical configuration using a three-phase armature winding is shown in FIG. In FIG. 1, windings L ₁ to _{L 3} of the multipolar magnetized permanent magnet rotor 1 and armature winding 3, respectively.
The rotational position of the position sensor 2 is detected by the position detector 2 and transmitted to the position signal switching circuit 5. Position signal switching circuit 5
has a 3-differential configuration, with each collector connected to each transistor of the corresponding output transistor group 6.
Connected to the base of Q ₁ to Q ₃ . The emitters of the output transistor group 6 are connected in common, and the collectors are respectively connected to one end of the corresponding phase of the armature winding 3. A common emitter of the output transistor group 6 is grounded via a resistor 7. The voltage at the ungrounded terminal 9 of the resistor 7 is applied to the inverting input (-) of the current output type differential amplifier circuit 4, and the torque command voltage 8 is applied to the non-inverting input (+) of the differential amplifier circuit 4. The output of the differential amplifier circuit 4 is applied to the position signal switching circuit 5 in a current mirror format. The other ends of the armature windings 3 are commonly connected and connected to a power source 10.

Now, the operation of FIG. 1 will be explained assuming that the transistor _Q1 is in a conductive state. armature current winding
The voltage flowing through the path L ₁ -> transistor Q ₁ -> resistor 7, and the voltage generated at terminal 9 of resistor 7 is compared with torque command input voltage 8, and automatically controlled by the negative feedback circuit so that both are equal. As a result, the armature current is controlled by the torque command voltage 8. That is, the torque generated by the motor is controlled by the torque command voltage 8. In addition, the power supply voltage is set high enough so that the transistor _Q1 does not become saturated in order to obtain the generated torque necessary for starting the motor and rotating the motor. Here, the collector of transistor _Q1
A voltage obtained by subtracting the voltage drop of the resistor 7, the voltage drop due to the DC resistance of the winding _L1 , and the back electromotive force of the winding _L1 due to motor rotation from the power supply voltage is applied between the emitters.

However, when the armature current is small or the motor rotation speed is low, the collector-emitter voltage of the transistor _Q1 is high, and the power consumption of the transistor _Q1 becomes large, which is disadvantageous in that the power loss is large. In addition, if the power supply voltage is lowered, transistor _Q1 will become saturated, and at that time, the base current will flow so that current also flows through transistors _Q2 or _Q3 , which should normally be non-conducting. A harmful armature current flows, resulting in a loss of torque or abnormal vibration.

These inconveniences are a major drawback in reducing the size and power consumption of equipment in which brushless motors are used.

Purpose of the Invention The present invention eliminates the drawbacks of the above-mentioned conventional example, and provides a brushless motor that stably prevents saturation of the output transistor, reduces power consumption of the output transistor, and eliminates unnecessary torque loss and abnormal vibration. It provides motors.

Configuration of the Invention The brushless motor of the present invention includes a multi-pole magnetized rotor, a multi-phase armature winding, and a position detector that detects the rotational position of the rotor and the armature winding. an output transistor group including a number of transistors equal to the number of phases that apply a current to the armature winding; a first current detection means for detecting the current in the armature winding; and the first current detection means. a first amplifier that amplifies the difference between the output signal of the output signal and the torque command input signal; and the output of the first amplifier is switched in accordance with the output of the position detector, and the output transistor group controls the energizing phase of the armature. a position signal switching means for determining the base current of the output transistor group; a second current detection means for outputting a signal corresponding to the base current of the output transistor group; and amplifying the difference between the respective output signals of the first and second current detection means. and a switching mode power supply for supplying power to the armature winding, and the switching mode power supply is configured to maintain a constant ratio between the current flowing through the first current detection means and the base current of the output transistor group. The second amplifier is configured to control the output voltage of the switching mode power supply so as to maintain the output voltage of the switching mode power supply. Therefore, unnecessary torque loss and abnormal vibration can be eliminated.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below based on the drawings. FIG. 2 is its configuration diagram. The permanent magnet rotor 1 is magnetized into eight poles, and the three-layer armature winding 3 is composed of windings L ₁ , L ₂ , L ₃ whose one ends are commonly connected to the output of the switching mode power supply 15. There is. The rotational position of rotor 1 and armature winding 3 is determined by position detector 2.
is detected by the position signal switching circuit 5 as a three-phase signal.
applied to. The position signal switching circuit 5 has a three-differential configuration using PNP transistors and drives an output transistor group 6. The output transistor group 6 consists of NPN transistors Q ₁ , Q ₂ , and Q ₃ whose emitters are commonly connected to the current detection resistor 7 . The non-inverting side input (+) of the differential amplifier circuit 4 which has two current output terminals 12 and 17 by a current mirror is connected to the supply terminal of the torque command voltage 8, and the inverting input (-)
is connected to a connection point 9 between the resistor 7 and the common emitter of the output transistor group 6. The output terminal 17 is connected to the common emitter of the position signal switching circuit 5,
The output terminal 12 is connected to a non-inverting input (+) of a differential amplifier 13 together with a resistor 11 whose one end is grounded. The inverting input (-) of the differential amplifier 13 is connected to the resistor 7.
and the transistor group 6, and the output is connected via a low-pass filter 14 to a voltage control input 16 of a switching mode power supply 15.

Next, the operation shown in FIG. 2 will be explained. The armature current flows through the switching mode power supply 15 → winding 1 → output transistor group 6 → resistor 7, and the negative A feedback loop controls the differential input of the differential amplifier circuit 4 to zero. Now, depending on the positional relationship between the rotor 1 and the armature winding 3, the output transistor Q ₁ ~
Assume that only transistor Q ₁ of Q ₃ is in a conductive state. Only the emitter current of transistor _Q1 flows through resistor 7. The base current I ₁ of the transistor Q ₁ is supplied from the current output terminal 17 of the differential amplifier circuit 4, and a current of the same magnitude is also supplied from the current output terminal 12 to the resistor 11. The values of resistor 7 and resistor 11 and the flowing current value are R ₇ and
If R ₁₁ and I ₇ and I ₁₁ are used, the input voltage V ₁₃ of the differential amplifier 13 becomes V ₁₃ =R ₁₁ ·I ₁₁ −R ₇ ·I ₇ (1). Also, if K≡I ₁ /I ₇ , then the current amplification factor h _FE of transistor Q ₁ can be written as h _FE = I ₇ /I ₁ -l, that is, h _FE = l/K-l ...(2) , I ₁ =I ₁₁ , so equation (1) becomes V ₁₃ =(R ₁₁ /l+h _FE −R ₇ )·I ₇ (3). Since the h _FE of the transistor Q ₁ changes with the collector _- emitter voltage V _{CE shown} in FIG. When the loop gain of the negative feedback loop composed of the resistor 7 is sufficiently high, the collector-emitter operating voltage of the transistor _Q1 is automatically determined so that the input voltage _V13 becomes zero. Therefore, from equation (3), h _FE = R ₁₁ /R ₇ −l (4). Since the right side of equation (4) is constant, h _FE of transistor Q ₁ is constant, and K=R ₇ /R ₁₁ . If the torque command voltage changes, the emitter current of transistor _Q1 also changes, and from Figure 3, the transistor
The collector-emitter voltage of _Q1 also changes automatically.
This voltage is determined by the characteristics of transistor _Q1 , and is the minimum voltage required to cause a specified emitter current to flow. Furthermore, since h _FE is automatically determined according to device variations and transistor temperature changes and is maintained at a constant value, transistor Q ₁ does not saturate and maintains an operating state with the lowest power consumption.
The output voltage of the switching mode power supply 15 is
Voltage drop due to DC resistance of L ₁ , transistor
It is equal to the sum of the collector-emitter voltage of Q ₁ , the voltage drop of resistor 7, and the motor back emf voltage, and the voltage of power supply 1
The difference from the voltage of 0 becomes an internal loss of the switching mode power supply 15. However, since it is a switching mode power supply, power efficiency is sufficiently high, and power loss due to changes in armature current or motor rotational speed is much smaller than when using a series control power supply. Further, the filter 14 is a low-pass filter and improves the stability of the negative feedback loop including the differential amplifier 13.

In the above embodiment, even if the rotational positions of the rotor 1 and the armature winding 3 change as the motor rotates, and which of the transistors Q ₁ to _{Q 3} becomes conductive changes, the same operation as described above will occur. transistor
The operating potential of Q ₁ to _{Q 3} changes stably in response to the winding current.

In addition, although the above-mentioned embodiment explained the case of three phases, the present invention is not necessarily limited to three phases, and various modifications (for example, the output side of the position signal switching circuit 5) are possible without changing the gist of the present invention. Insert a current amplification circuit into the
How to increase the value of or current output terminal 1
It goes without saying that there are many applications, such as a method of changing the value of the resistor 17 by setting the current ratio of 2 and 17 to a value other than 1.

Effects of the Invention As explained above, in the brushless motor of the present invention, the collector-emitter voltage is controlled by a switching mode power supply so that the output transistor has a constant current amplification factor that can be determined in advance by a resistor. By suppressing the power loss of the output transistor to the necessary minimum and preventing saturation of the output transistor, unnecessary torque loss and abnormal vibration can be eliminated. Further, since the collector-emitter operating voltage of the output transistor automatically follows device variations, operating current, or transistor temperature, extremely stable operation can be obtained. Therefore, it is particularly effective in reducing the size and power consumption of equipment using brushless motors.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional brushless motor.
FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a graph showing the relationship between collector-emitter voltage and current amplification factor of a transistor. DESCRIPTION OF SYMBOLS 1... Rotor, 2... Position detector, 3... Armature winding, 4... Differential amplifier circuit, 5... Position signal switching circuit, 6... Output transistor group, 7, 11...
...Resistor, 8...Torque command input voltage, 13...Differential amplifier, 14...Filter, 15...Switching mode power supply.

Claims (1)

[Scope of Claims] 1. A multi-pole magnetized permanent magnet rotor, a multi-phase armature winding, a position detector that detects the rotational position of the rotor and the armature winding, and the an output transistor group consisting of a number of transistors equal to the number of phases for applying a current to the armature winding; a first current detection means for detecting the current in the armature winding; a first amplifier that amplifies the difference between the output signal and the torque command input signal;
position signal switching means for switching the output of the first amplifier according to the output of the position detector and determining the energization phase of the armature winding by the output transistor group; a second current detection means for outputting a signal output from the first current detection means, a second amplifier for amplifying the difference between the output signals of the first and second current detection means, and a switch for supplying power to the armature winding. a switching mode power supply, the output voltage of the switching mode power supply is controlled by the output of the second amplifier so as to maintain a constant ratio between the current flowing through the first current detection means and the base current of the output transistor group. A brushless motor that controls the 2. A current mirror and a resistor are used as the second current detection means, a current output type differential amplifier is used as the first amplifier, and the current output is distributed between the position signal switch and the resistor by the current mirror. ,
2. The brushless motor according to claim 1, wherein the voltage across the resistor is the output of the second current detection means. 3. The brushless motor according to claim 1, further comprising a low-pass filter inserted between the second amplifier and the switching mode power supply.