Epson PX-8 Technical Manual page 153

REV.-A
The principle of the motor speed control can be illustrated by Fig. 3-8.
V R1 R5
Pin 1
100 K 150K
R6
Pin 2
1 K
--
L
I
I
I
I
I
I
I
circuit
Regulated
power
supply
llJU1JL
JUlillL
./
OUT I-----=~ Integrating
) circuit
-1lJLJlJ1JL
Fig. 3-8 Motor Speed Control Circuitry
Integrating Circuit
The IC output is a pulse signal as shown in Fig. 3-9. However, the capstan motor cannot be con-
trolled by a pulse signal as the motor would oscillate. The IC output is integrated by the next
stage integrating circuit, which uses the external capacitors C3 and C4. The pulse delay time (t) is
determined by the capacitance of C4.
Fig. 3-9 Integrating Circuit
Current Control
The output current from the integrating circuit is amplified and the amplified current is limited to a
proper value by the external resistor R3. Fig. 3-10 conceptually illustrates the principle.
VBSW
C>----.
Speed control
Fig. 3-10
3-7
'--_-, Current limiter
resistor
Capstan motor
/