JPS613349A - Pwm system motor drive circuit of vtr - Google Patents

Abstract

PURPOSE:To reduce influences of switching of a PWM circuit upon an ATF servo circuit by locking the output frequency of the PWM circuit to a frequency different from the frequency of a pilot signal used in an ATF system tracking servo circuit. CONSTITUTION:In a drive circuit 1, the rotative speed of a drum motor 2 is detected by a frequency generator 5, and the pulse width of an output P1 of a PWM circuit 9 is controlled in accordance with the detection signal. In a drive circuit 3, the rotative speed of a capstan motor 4 is detected by a fequency generator 10, and the pulse width of an output P2 of a PWM circuit 14 is controlled in accordance with the detection signal. The motor 4 is provided with an ATF system phase servo loop using the pilot signal consisting of frequencies f1-f4. A locking reference pulse P3 is applied to an input terminal 15, and the frequency of the pulse P3 is set to a frequency fs different from frequencies f1-f4, and frequencies of pulses P1 and P2 are locked to f5. Thus, influences upon the ATF servo circuit are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a PWM type motor drive circuit that can be applied to a drum motor and a capstan motor in a V'l'H that performs tracking servo using the ATF type. It is.

BACKGROUND TECHNOLOGY AND PROBLEMS In a compact and lightweight VTR such as a so-called 8 mm video, a PWM type drive circuit is used as a drive circuit for a drum motor and a capstan motor.

The PWM type drive 4-drive circuit is configured to control a PWM circuit using a control signal according to the speed of the motor.The output pulse of this PWM circuit switches a transistor, and the switching output is rectified and smoothed to control the motor. A DC voltage corresponding to the speed of the motor is obtained, and this DC voltage is supplied to the coil of the motor. This kind of PWM
This type drive circuit is small and consumes low power, making it suitable for small and lightweight VTRs.

The frequency of the output pulse of the PWM circuit in the PWM drive circuit is selected to be about 'lQ[] KHz. This frequency is determined in consideration of conditions such as the heat generation of the transistor switched by the output pulse and the size of the ink-tance coil that rectifies the switching output of this transistor.

However, the frequency actually varies by about 30 to 40 degrees due to variations in circuit elements and the like.

On the other hand, due to the VTR's tracking servo system, A T
F (Automatic Tracking Fin
ding) method has been proposed. ATF type tracking servo uses husband frequencies f1, f2, f3 . f4
The capstan motor is controlled so that two pilot signals obtained from both adjacent tracks have the same magnitude during playback. There are two types of servo system. With this ATF method, the conventional control head can be omitted, so the Vo
This is useful for downsizing the LT.

For example, as the frequency of the above four pilot signals, f1=
102.544KHz, f2=118.951KH
z, f3=165.21 QKHz, f4=1
48.689KHz is proposed. Therefore, the range of these frequencies f1 to f4 includes the output frequency of the aforementioned PWM circuit, which is approximately 1QQKHz. For this reason, PW
AT by switching transistors by M circuit
F servo circuit is affected. Particularly in the case of a small V'lR, the PWM circuit and the servo circuit are arranged close to each other, so the influence is large. During VTR playback, biloft signals f1 to f4 are detected using steep filters, but if the switching frequency of the PWM circuit matches or approaches one of f1 to f4 due to variations in circuit elements, Interference waves caused by switching may affect the servo circuit, causing the servo circuit to malfunction.

OBJECTS OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems in a VTR equipped with an ATF type tracking servo circuit, a PWM motor, and a data drive circuit.

SUMMARY OF THE INVENTION The present invention locks a PWM circuit using a signal having a frequency different from that of a pilot signal. This results in A due to switching of the PWM circuit.
The influence on the TF servo circuit can be reduced.

Example FIG. 1 shows a first embodiment of the invention.

In FIG. 1, 1 indicates a drive circuit for a drum motor 2, and 3 indicates a drive circuit for a capstan motor 4.

In the drive circuit 1, the rotation speed of the drum motor 2 is detected by the frequency generator 5, and this detection signal is amplified by the sensor amplifier 6 and applied to the servo circuit 7. The servo circuit 7 outputs a control signal according to the detection signal, and this control signal is amplified by the linear amplifier 8 and sent to the PWM circuit 9.
, and controls the pulse width of the output pulse P1 of this PWM circuit 9.

The PWM circuit 9 is configured as an IC circuit together with the linear amplifier 8, and is oscillated at a fixed frequency by a capacitor C1 externally connected to this IC circuit.

The pulse P1 switches the transistor Q1,
The switching output obtained from the collector of this transistor Q1 is rectified and smoothed by a flywheel diode D1, an inductance coil L1, and a capacitor C2, thereby becoming a DC voltage (1) corresponding to the rotation speed.

By supplying this DC voltage ■1 to the motor 2,
The rotational speed of this motor 2 is controlled to be constant.

In the drive circuit 3, the rotational speed of the capstan motor 4 is detected by a frequency generator 10, and this detection signal is amplified by a sensor amplifier 11 and applied to a servo circuit 12. The servo circuit 12 outputs a control signal according to the detection signal, and this control signal is amplified by the linear amplifier 13 and applied to the PWM circuit 14.
The pulse width of the output pulse P2 is controlled.

The PWM circuit 14 is configured as an IC circuit together with the linear amplifier 13, and a capacitor C is externally connected to this IC circuit.
It oscillates at a frequency determined by 3. The above pulse P2
switches the transistor Q2, and the switching output obtained from the collector of this transistor Q2 is connected to the flywheel diode D2 and the inductance coil L2.
And by being rectified and smoothed by capacitor C4,
The DC voltage becomes 2 depending on the rotation speed. This DC voltage
2 is supplied to the motor 4, so that the rotational speed of the motor 4 is controlled to be constant. In addition to the speed servo loop described above, the Capnutan motor 4 is also provided with a phase servo (tracking servo) loop (not shown) according to the A'I'Ii' method. This phase servo controls the trunking of the rotary head with respect to the video track during playback.

At one point, a locking reference pulse P3 having a predetermined frequency is applied to the input terminal 15. As this reference pulse P3, a pulse with a high frequency accuracy of 5 is used. For example, it is possible to use the clock pulse etc. obtained from the digital circuit of ■1"R. The frequency f5 of this reference pulse P3 is selected to be a value different from the frequencies f1 to f4 of the four pilot signals described above, for example, 110 KH2. The reference pulse P3 is differentiated by a differentiating circuit 16, this differentiated pulse is applied to a waveform shaping circuit 17, and the positive polarity of the differential pulse is waveform-shaped to obtain a lock pulse P4.

This lock pulse P4 is inverted by an inverter 18, and this inverted pulse P4 is applied to the base of transistor Q3. Therefore, this transistor Q3 is activated by the above-mentioned pulse P4.
(7) The capacitor C1 is charged by the current that is conducted during the pulse width period and output from its collector. PWM
The circuit 9 is configured to form an output pulse P1 based on a triangular wave voltage of a predetermined frequency and a predetermined level formed by charging and discharging the capacitor C1. Therefore, since the charging current from the PWM circuit 9 and the charging current from the transistor Q3 flow into the capacitor C1, 1. As shown in FIG. 2, the above triangular wave voltage is
In the portion tl, it increases rapidly and reaches a predetermined level Eo. This forces the edge of the output pulse P1 to be reset, and as a result, the frequency of this pulse P1 is f5
is locked.

On the other hand, the lock pulse P4 is applied to the base of the transistor Q4 to make the transistor Q4 conductive, and the collector of the transistor Q4 is connected to the reset terminal 14a. Therefore, when transistor Q4 becomes conductive, capacitor C4 is forcibly discharged, and this discharge current flows through transistor Q4. As a result, as shown in FIG. 3, the triangular wave voltage VT generated by the PWM circuit 14
2 is forcibly reset to zero level. As a result, the frequency of the output pulse P2 is locked to f5.

Note that the PWM circuit 9 may have a reset terminal, and the P'VJM circuit 14 may have no reset terminal 14a.

Also, the capacitor C1 externally connected to the PWM circuits 9 and 14
, C3 are selected such that the free-running oscillation frequency of the PWM circuits 9, 14 is lower than the lock frequency f5 when the transistors Q3 and C4 are not connected.

For example, when f5=110KH2, the capacitance of C1°C3 is selected to such a value that the free-running oscillation frequency becomes about 8Q KHz.

According to this embodiment, transistor Q1. C2 switching pulse P1. P2 frequency or the frequency f1 of the four pilot signals used in the ATF servo circuit
~f4 is locked to a different frequency f5, so transistors Q1. It is possible to prevent the switching of Q2 from affecting the tracking servo during playback.

FIG. 4 shows a second embodiment of the present invention, in which the same parts as in FIG. 1 are given the same reference numerals.

In this embodiment, a variable capacitor C5 is connected externally to the PWM circuit 9 in parallel to the capacitor C1. Also, the triangular wave voltage V obtained across these capacitors C1 and C5
T1 is added to the comparator 20 and compared with the reference voltage (2). From this comparator 2°, VTl>V,
At this time, a lock pulse P5 is obtained, and this lock pulse P5 is applied to the reset terminal 14a of the PWM circuit 14.

According to the above configuration, the output frequency of the PWM circuit 14 is PWM
It is locked to the free-running oscillation frequency of the M circuit 9. By adjusting the free-running oscillation frequency with the capacitor C5, interference caused by switching can be removed by selecting the frequency f5 as in the case of the first embodiment.

This second embodiment is based on the reference pulse P in the first embodiment.
This is suitable for use in cases where there is no pulse suitable for use as pulse number 3 inside the VTR. In addition, in Fig. 4, P
The frequency of the WM circuit 9 may be locked to the free-running frequency of the PWM circuit 14.

Effects of the Invention Switching disturbances exerted on the ATF tracking servo circuit of the PWM drive circuit can be effectively removed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention;
3 and 3 are signal waveform diagrams of the main parts of FIG. 1, and FIG. 4 is a block diagram showing a second embodiment of the present invention. In addition, in the symbols used in the drawings, 2......Dry motor 4...
・・・・・・・・・・・・Capstan motor 9.1
4...PWM circuit Q1, Q2...
...Switching transistor Q3. Q4...
...Transistor P4. P5...Lock pulse.

Claims (1)

[Claims] In a VTR equipped with an ATF type tracking servo circuit and a PWM type motor drive circuit, the PW
A PWM motor drive circuit for a VTR in which the output frequency of the M circuit is locked to a frequency different from the frequency of a pilot signal used in the ATF tracking servo circuit.