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Vcc
12
Refout
14
GND
7
Rt
6
Ct
5
Dead time control
4
Non-reverse input
1
2
Reverse input
Non-reverse input
16
Reverse input
15
Feedback
3
(C) PWM circuit
This circuit integrates the speed deviation signal and the phase difference signal and modulates the pulse width after adding the phase compensa-
tion. The IC8 is the PWM generator which includes the error amplifier, and saw teeth wave generator, the comparator, and the output buffer. R124,
R125, R136, C51, and C54 are connected to the error amplifier in the IC8, forming the integral/phase compensation circuit. R65 and C45 set the
frequency of saw teeth wave. It is about 25KHz for this circuit.
The integrated deviation signal is voltage-compared with the saw teeth wave by the PWM comparator to be the pulse signal of duty ratio in
proportion to the deviation signal voltage. The comparator for adjusting the OFF period is also included in the IC8. By inputting a voltage to 4 pin, the
OFF period of the PWM signal is increased. The LOW level period of IC8 PWM output (8 pin) becomes short when the paper feed motor rotation
speed is increased, and the HIGH level period becomes shorter when the rotating speed is decreased.
(D) Overshoot prevention circuit
When the paper feed motor is raised to the low speed state, the speed is accelerated at a moment. Therefore, the OFF period of the PWM signal is
made longer to limit the power supply to the paper feed motor.
This circuit integrates the low speed rising signal (PWM) outputted from IC13 (G/A) with R92 and C37, and passes it to the IC8 4 pin.
The input voltage integrated by the PWM duty is constant. The time duration is set according to the rising time.
Reference
Low input erroneous
voltage input
operation preventing
circuit
circuit
Oscillation
circuit
Dead time comparator
Error amplifier 1
PWM comparator
Error amplifier 2
IC8 internal circuit
13
Output control
T
F/F
– 29 –
8
PWM output
9
11
PWM output
10
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