JPH04117189A - Motor control circuit - Google Patents

Abstract

PURPOSE:To improve a decrease in a torque when a motor is started by enhancing the frequency of a clock pulse for a predetermined time after the motor is started. CONSTITUTION:Since a clock pulse having a high frequency of a carrier generator 21 is selected at the time of starting a motor, a motor current rises, and then a current detector 15 operates. The conducting period of the motor current until the output current of an output amplifier 13 is interrupted is near the period of the pulse, and hence a time when the motor current is turned OFF, is shortened. Accordingly, the effective value of the motor current can be increased, and an effective torque at the time of starting can be increased. On the other hand, a clock pulse having a low frequency of a carrier generator 22 is selected at the time of a steady rotation. Therefore, a conflict requests of an increase in a starting torque at the time of starting the motor and a reduction in power loss of an output transistor at the time of steady rotation can be compatible.

Description

[Detailed Description of the Invention] [Summary] Regarding a control circuit for driving a motor, an object of the present invention is to provide a PWM type motor control circuit that improves the torque drop at the time of starting the motor and has less power loss during steady operation. P that supplies the motor with an output current that is pulse width modulated by a clock pulse of a constant frequency, and cuts off the output current when the peak value exceeds a predetermined value.
In a WM type motor control circuit, the frequency of the clock pulse is increased for a certain period of time after the motor is started.

[Industrial application field]

The present invention relates to a control circuit for driving a motor, and particularly to a motor control circuit suitable for driving a pulse width modulation (PWM) type motor of a magnetic disk device.

In recent years, in magnetic disk drives, there has been a decrease in torque due to higher rotation speeds, an increase in windage loss due to an increase in the number of disks,
Torque loss increases due to an increase in friction loss with the disk due to an increase in the number of heads, and as a result, there is a tendency for torque to be insufficient, especially at the time of startup.

However, when the carrier frequency during pulse width modulation is increased in order to increase the starting torque, problems arise such as increased power loss in the output transistor.

Therefore, there is a need for a motor control circuit that does not cause a decrease in torque during startup and does not cause an increase in power loss of the output transistor even during steady operation.

[Prior Art] In a conventional PWM motor drive circuit, the carrier frequency of the pulse is constant when the duty ratio of the pulse is controlled by the PWM method.

FIG. 4 is a block diagram showing the configuration of a conventional motor control circuit, in which 11 is a carrier generation circuit that generates clock pulses for pulse width modulation, 12 is a PWM circuit that performs pulse width modulation, and 13 is a PWM circuit. 14 is a motor for driving the magnetic disk; 15 is a current detection circuit that detects overcurrent to the motor 14; 16 is a speed encoder that detects the rotational speed of the motor 14; This is a speed controller for controlling the rotational speed of the motor 14.

When the PWM circuit 12 receives a motor start signal, it rises in response to a clock pulse from the carrier generation circuit 11 and generates a pulse signal whose pulse width changes depending on the magnitude of the control signal from the speed controller 17.

The output amplifier 13 generates an output current corresponding to the output pulse signal of the PWM circuit 12 and supplies it to the motor 14.

Speed encoder 16 generates a speed detection signal whose magnitude changes depending on the rotational speed of motor I4. The speed controller 17 uses a speed command signal given from the outside as a reference value, compares the speed detection signal from the speed encoder 16 with this, generates a control signal corresponding to the error, and performs PWM control.
By supplying the signal to the circuit 12, feedback control that follows the speed command is performed.

On the other hand, the current detection circuit 15 detects the current of the motor 14, and when the current exceeds a predetermined peak current value, controls the PWM circuit 12 to cut off its output pulse signal, so that the output current supplied to the motor 14 is also blocked.

FIGS. 5(a) and 5(b) show the output current and clock pulse waveforms of the motor control circuit in FIG. Shows when rotating.

When the motor is started, the torque of the motor is large, so the motor current is large, so the current detection circuit 15 operates at an early stage, and the period during which the motor current flows is short as shown in FIG. 5 (al).

On the other hand, during steady rotation, the motor torque is small, so the motor current is small and does not reach a level at which the current detection circuit 15 operates, so the motor current is not cut off.

(Problem to be solved by the invention) In conventional motor control circuits, the effective current value of the motor is changed by keeping the frequency of the clock pulse that performs pulse width modulation constant and changing the duty ratio of the output current pulse. , controls the speed of the motor that drives the magnetic disk.

However, at startup, the motor current is large, so
The current detection circuit operates quickly. When the current detection circuit operates, until the rise of the next clock pulse,
Since the current supplied to the motor from the output amplifier is in an off state, the current supplied to the motor 14 becomes effectively smaller as the duty ratio decreases, and therefore,
Generated torque decreases.

As described above, when the current detection circuit operates at the time of starting the motor, the duty ratio of the output pulse current decreases and the torque decreases, so there is a problem that the starting is slow and it takes time to reach steady rotation.

In addition, in order to increase the starting torque of the motor, the clock pulse frequency of the carrier generation circuit is increased to increase the effective current regardless of whether the motor is starting up or rotating steadily. This increases the number of times the output amplifier transistor is switched. There are problems in that power loss increases and noise increases.

The present invention aims to solve the problems of the prior art as described above, and aims to improve the torque drop at the time of motor startup and to provide a PWM system that does not increase power loss in the output circuit.
The system is intended to provide a motor control circuit.

[Means for Solving the Problems] As shown in the principle structure of the present invention in FIG. In a PWM type motor control circuit that cuts off the output current when the value exceeds the current value, the frequency of the clock pulse is increased for a certain period of time after the motor 14 is started.

The present invention also provides a driving means 1 that supplies an output current that is pulse width modulated to the motor 14 in accordance with a clock pulse, and detects a peak value of the output current and outputs an output from the driving means 1 when the peak value of the output current exceeds a predetermined value. In a PWM motor control circuit equipped with current limiting means 2 for cutting off current, the first carrier generating means 3 generates a high frequency clock pulse, and the second carrier generating means 4 generates a low frequency clock pulse. generating a clock pulse and by the timer means 5;
A certain period of time is counted from the start of the motor 14, and the selection means 6
Accordingly, the first
carrier generating means 3 or second carrier generating means 4
This clock pulse is selected and supplied to the driving means 1.

[Effect]

In a PWM type motor control circuit that supplies an output current that is pulse width modulated to a motor using a clock pulse with a constant J'1 wave number and cuts off the output current when the peak value exceeds a predetermined value, the output current is constant after the motor is started. By increasing the frequency of the time clock pulse, it is possible to increase the effective torque while limiting the peak current when starting the motor, while at the same time increasing the power loss of the output amplifier transistor and reducing noise during steady rotation. It never occurs.

In a PWM type motor control circuit that supplies a pulse width modulated output current to a motor in accordance with a clock pulse, detects the peak value of the output current, and cuts off the output current when it exceeds a predetermined value, Generates a high frequency clock pulse and a low frequency clock pulse, counts a certain amount of time from the start of the motor, and selects a high frequency clock pulse or a low frequency clock pulse depending on when the counting ends. Since the output current is pulse-width modulated, it is possible to increase the effective torque while limiting the peak current when starting the motor, and at the same time, during steady rotation, the power loss of the output amplifier transistor is reduced. It does not increase or generate noise.

〔Example〕

FIG. 2 is a diagram showing an embodiment of the present invention, in which the same parts as in FIG. 22 is a second carrier generation circuit that generates a low-frequency clock pulse, 23 is a timer circuit that counts a certain period of time from the motor start signal manually, and 24 is a selection circuit that selects the output of the carrier generation circuits 21 and 22. be.

The timer circuit 23 controls the selection circuit 23 to select the high frequency clock pulse of the carrier generation circuit 21 for a certain period of time after the motor start signal is input until the motor 14 reaches steady rotation, and counts the clock pulses. After this is completed, the selection circuit 23 is controlled to select the clock pulse of the carrier generation circuit 22 having a low frequency.

3(a) and 3(b) are diagrams showing the output current and clock pulse waveforms of the motor control circuit of FIG.
(a) shows the time when the motor is started, and (b) shows the time when the motor rotates steadily.

When starting the motor, as shown in FIG. 3 Ta), the high frequency clock pulse of the carrier generation circuit 21 is selected, so the current detection circuit 15 operates after the motor current rises, and the output amplifier 13 The period during which the motor current flows until the output current is cut off is close to the period of the clock pulse, so the time during which the motor current is turned off is shortened, so the effective value of the motor current can be increased. Effective torque at startup can be increased.

On the other hand, during steady rotation, the low frequency clock pulse of the carrier generation circuit 22 is selected as shown in FIG. 3(b), so the motor current in this state is as shown in FIG. 5(b).
This is no different from the conventional case shown in .

Therefore, according to the motor control circuit shown in FIG. 2, it is possible to satisfy the contradictory demands of increasing the starting torque when starting the motor and reducing the power loss of the output transistor during steady rotation. become.

Note that the present invention is applicable not only to magnetic disk devices but also to P.
This is generally applicable to WM type motor drive circuits.

(Effects of the Invention) As explained above, according to the present invention, in a PWM type motor control circuit, it is possible to increase the effective torque while limiting the peak current when starting the motor, and at the time of steady rotation. There is no increase in power dissipation in the transistors of the output amplifier or generation of noise.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the basic configuration of the present invention, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 (a) and (b) are diagrams showing the output current of the motor control circuit in Fig. 2. Figure 4 is a block diagram showing the configuration of a conventional motor control circuit. 2 is a diagram showing waveforms. 2 is a driving means, 2 is a current limiting means, 3 is a first carrier generating means, 4 is a second carrier generating means, 5 is a timer means, 6 is a selection means, and 14 is a motor. be.

Claims (1)

[Claims] 1) A P that supplies an output current that is pulse width modulated by a clock pulse of a constant frequency to the motor (14) and cuts off the output current when its peak value exceeds a predetermined value.
A WM type motor control circuit, characterized in that the frequency of the clock pulse is increased for a certain period of time after the motor (14) is started. (2) a driving means (1) for supplying an output current pulse-width-modulated in accordance with a clock pulse to the motor (14); In a PWM motor control circuit, the circuit includes a current limiting means (2) for cutting off the output current from 1), a first carrier generating means (3) for generating a high frequency clock pulse, and a low frequency clock. a second carrier generating means (4) that generates pulses; a timer means (5) that counts a certain period of time from the start of the motor (14); 1st
The clock pulse of the carrier generating means (3) or the second carrier generating means (4) is selected to drive the driving means (1).
) A motor control circuit characterized in that it is provided with selection means (6) for supplying the voltage to the motor.