JPS5936145Y2 - Switching regulator type motor drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a switching regulator type motor drive circuit suitable for application to, for example, driving a VTR motor.

First, a conventional switching regulator type motor drive circuit will be described with reference to FIG.

Reference numeral 11 denotes a motor, such as a capstan motor for a VTR.

This motor 11 can be used not only to drive carbmethane, but also to drive a reel and automatically wind a tape from a tape cassette around a tape guide drum.

1 is a switching circuit for this motor 11, PN
P-type transistor Ql and NPN-type transistor Q2 are connected to each other at their collectors, power supply element B is connected to the emitter of transistor Q1, and transistor Q2
The construction is made up of □ ivy that is grounded.

2 is a pulse width modulation circuit that supplies a switching control signal to the switching circuit 1;

This pulse width modulation circuit 2 is composed of a level comparator CM and an integrating circuit 4.

3 is a signal generation circuit that generates a carrier wave pulse signal to be supplied to the pulse width modulation circuit 2;

This is composed of a rectangular wave pulse oscillator 8 made of, for example, a crystal oscillator, and a frequency division counter 7 that divides the frequency of the oscillation output.The frequency division counter 7 is composed of one or more stages of flip-flop circuits. ing.

A rectangular wave pulse signal having a predetermined frequency and a duty of 50 yen is supplied from the frequency dividing circuit 7 to the integrating circuit 4 of the pulse width modulation circuit 2 as a carrier wave pulse signal.

The integrating circuit 4 is composed of a resistor 5 and a capacitor 6, and a triangular wave signal is obtained at its output side.

Also, the output side of the switching circuit 1 is a low-pass filter 10.
The low-pass filter 10 and the motor 11 constitute a load 9.

A rotation detection signal of the motor 11 (its detection means is not shown) is supplied as a detection signal of the load 9 to the level comparator CM from the input terminal t.

Then, from the level comparator CM, the carrier wave pulse signal is pulse width modulated, that is, its duty is changed by level comparison between the triangular wave signal from the integrating circuit 4 and the rotation detection signal accompanying the rotation of the motor 11. A pulse width modulated signal is obtained, which is supplied as a switching control signal to the switching circuit I17.

From the switching circuit 1, a bell comparator CM,
A rectangular wave pulse signal is obtained by inverting the phase of the rectangular wave output, which is rectified by the low-pass filter 10 and then supplied to the motor 11 as a drive current.

However, the switching regulator type motor drive circuit described above has the following problems.

When the signal generation circuit 3 stops generating the carrier wave pulse signal, that is, when the oscillation of the rectangular wave pulse oscillator 8 stops or the rise of oscillation is delayed, the output of the frequency division counter 7 becomes high There are cases of /L and cases of low level, and it cannot be determined uniquely.

This can be understood from the properties of flip-flop circuits.

If the generation of the carrier wave pulse signal from the signal generating circuit 3 stops and it is not possible to determine whether the output is high level or low level, there is a risk that the motor 11 may stop or run out of control. I can't predict that (・.

That is, when the output of the frequency division counter 7 is at a high level, the output of the pulse width modulation circuit 2 is at a low level, the output from the switching circuit 1 is at a high level, and the motor 11 runs out of control.

Also, when the output of the frequency division counter 7 is low level, the output of the pulse width modulation circuit 2 is high level, the output of the switching circuit 1 is low level, and the motor 11 stops rotating. If the signal generation circuit 3 does not generate a normal carrier wave pulse signal, it is not determined whether the motor 11 will stop or run out of control (For example, if the motor 11 is a capstan motor as described above, the signal Generation circuit 3
If the motor 11 runs out of control while generating a normal carrier wave pulse signal, there is a risk of applying excessive tension to the magnetic tape or scratching the tape, thereby damaging the tape.

Therefore, in this case, it is necessary that the motor 1 is always stopped.

Also, if the motor 11 is a drum motor of a VTR,
If the motor 11 stops when the carrier wave pulse signal is not generated from the signal generation circuit 3, an air film will not be formed between the rotating drum and the magnetic tape.
In this case, it is better to let the motor 11 run out of control.

In view of this, the present invention provides a switching regulator type motor drive circuit in which, when the generation of the carrier wave pulse signal from the signal generation circuit stops, f, the current flowing through the load, that is, the motor, is fixed at a predetermined value. The purpose of this article is to propose something that will be implemented in a similar manner.

An embodiment of the present invention will be described below with reference to FIG. 2, and parts corresponding to those in FIG.

The embodiment shown in FIG. 2 is for a motor switching regulator as in the case shown in FIG. Sometimes motor 11
In the present invention, in the switching regulator type motor drive circuit as described above, a capacitive coupling circuit 12 is interposed between the signal generation circuit 3 and the pulse width modulation circuit 2. This is what I inserted.

The capacitive coupling circuit 12 in this case is configured as follows.

In the circuit 12, a bypass filter 14 consisting of a capacitor 15 and a resistor 16 is provided on the output side of the frequency dividing counter 7.
is connected, and the buffer 7 circuit 13 is connected to the next stage.

The output side of this buffer circuit 13 is connected to the input side of the integrating circuit 4.

The other configurations are the same as in FIG. 1. In this way, when the signal generating circuit 3 is also generating the carrier wave pulse signal normally, the motor 11 is normally servoed and rotates as in the case of FIG.

Further, when the signal generating circuit 3 does not generate a carrier wave pulse signal, the output of the frequency dividing counter 7 remains at a high level or a low level.

In any case, the level does not change over time, so
The input side of the buffer circuit 13 is at a low level, and therefore its output side is also at a low level.

Therefore, the output side of the level comparator CM becomes high level,
The output side of the switching circuit 1 is at a low level t (the remoter 11 will stop rotating).

In this case, in order to prevent the motor 11 from running out of control when the signal generating circuit 3 does not generate a normal carrier wave pulse signal, either connect the grounding end of the resistor 16 of the bypass filter 14 to the power supply +B side, or Alternatively, an inverter circuit may be used as the buffer circuit 13.

According to the present invention described above, even if the generation of the carrier wave pulse signal from the signal generation circuit stops, the motor drive current is fixed at a predetermined value regardless of the state of the frequency dividing flip-flop circuit. A switching regulator type motor drive circuit can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional switching regulator type motor drive circuit, and FIG. 2 is a circuit diagram showing an example of a switching regulator type motor drive circuit according to the present invention. 1 is a switching circuit, 2 is a pulse width modulation circuit, 3 is a signal generation circuit, CM is a level comparator, 4 is an integration circuit, 7 is a frequency division counter, 8 is a rectangular wave pulse oscillator, 9 is a load, 1
0 is a low-pass filter, 11 is a motor, 12 is a capacitive coupling circuit, 13 is a buffer circuit, 14 is a bypass filter, and 15 is a capacitor.

Claims (1)

[Scope of utility model registration request] A motor connected to the switching circuit, comprising a switching circuit, a pulse width modulation circuit that supplies a switching control signal to the switching circuit, and a signal generation circuit that generates a carrier pulse signal to be supplied to the pulse width modulation circuit. A switching regulator type motor drive circuit is configured to drive the motor by supplying the rotation detection signal of the signal generator as a modulation signal to the pulse width modulation circuit. A switching regulator type motor drive circuit with a capacitive coupling circuit inserted between the width modulation circuit.