M51971 Ver la hoja de datos (PDF) - MITSUBISHI ELECTRIC

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M51971

MOTOR SPEED CONTROL

MITSUBISHI ELECTRIC  

MITSUBISHI <CONTROL / DRIVER IC>

M51971L/FP

MOTOR SPEED CONTROL

Brief Description on M51971 Operation

Block Description

Amplifier Schmitt

output input

Timer

Non-inverted input 1

3

FG amplifier

VLS 1.9V

Operational

amplifier

Inverted input 2

D1

4

Schmitt

circuit

B

A

A’

Logic for timer

VLS 1.9V

D2

E

To pin 6

Rτ

C

5

Q1

Cτ

7.5k

comparator

15k

D

M

Buffer

I

9

OP

100Ω

Over-shoot

prevention signal

Over-shoot prevention circuit

G Logic for over-shoot

Q3

prevention

H

CF1

8

RF

CF2

Timer output

206µA

I1

Q2

16µA

I2

Constant current

control

Stabilized

power

supply

10

Power

supply

7 GND

6

Stabilized voltage

FG amplifier

The FG amplifier consists of an operational amplifier, revel shift

circuit and diode for waveform clip.

When a DC block capacitor is connected to pin 2 , output DC

voltage at pin 3 becomes higher than DC voltage at pin 1 by VLS

(≈1.9V≈3VBE).

AC signals centering around the GND can be therefore amplified

easily. The clipper diode limits the output signal amplitude to

±0.7V (VBE) max. and rapidly charges DC block capacitor with

power supply turned ON.

Schmitt circuit

The Schmitt circuit is a comparator with histeresis, and has ON

level of VLS + 20mV and OFF level of VLS - 20mV.

Timer

The timer generates basic time necessary for controlling the

speed.

This timer is a one-shot circuit triggered with input signals and

generates pulse of 1.1 Cτ Rτ in pulse width.

Constant current control circuit

The constant current control circuit is controlled with output of timer

circuit. The circuit generates, at pin 8 , source current of I1 – I2

(≈190µA) for the period without one-shot pulse and generates sink

current of I2 (≈16µA) for the period with one-shot pulse.

The ratio of I1 to I2 is characteristic to the IC. The frequency of the

tacho-generator to be set is determined by the one-short pulse

width and this current ratio (I1 / I2 ≈12.6).

TG = Tτ x

I1

I1–I2

≈ 1.09 x Tτ

Where:

TG : Tacho-generator signal frequency (set value)

Tτ : One-short pulse width

Over-shoot prevention circuit

The over-shoot prevention circuit operates when over-shoot is

large in particular, e.g. the motor is suddenly released from lock

status.

Q3 is set to ON for the period of one-short pulse width (Tτ) when

the signal period of the tacho-generator in a motor is shorter than

the one-shot pulse. Generally, electric charge of CF1 is discharged

for this period due to RF • CF2 >>Tτ.

Buffer amplifier

The buffer circuit is a voltage follower circuit using an operational

amplifier. The input current is very small (10nA max.) and the

circuit can drive the output current of 20mA.

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