Epson LQ-2550 Technical Manual page 74

2.2.2 Input Filter Circuit
Figure 2-19 shows the input filter circuit. The input filter circuit attenuates external harmonics (noise)
on the AC input line, and inhibits noise generated by the circuits in the printer from going out over the
AC line. The coils and capacitors employed in this filter have been chosen to be able to handle
fluctuations of the AC input line. The frame grounds (F. G.) connected between C2 and C3, and C5 and
C7 are for leakage current from the AC line to the frame.
SW
(#8 CO)
I
2.2.3 Rectifier, Smoothing, and Surge-suppression Circuits
Figure 2-20 shows the rectifier, smoothing, and surge-suppression circuits. The filtered AC input voltage
from the input filter is input to diode bridge DB 1, full-wave rectified, and smoothed by capacitor Cl 2. .
Normally, the voltage across C 12
shorted at C 12 via DB 1 when viewed from the input side. Therefore, when the power is first turned
on, a large charging current flows to C 12. This current is known as a surge current. If the power switch
is turned on again when the input voltage is near its peak, the maximum surge current will flow (See
point @ in Figure 2-2 1.).
INPUT
FILTER
CIRCUIT
>
Figure 2-20. Rectifier, Smoothing, and Surge-suppression Circuits
I
Figure 2-19. Input Filter Circuit
O V before the printer power is turned on. This means the line is
is
DB1
D6
R8
T2
10 n Sw
2-27
IL2
I
FET
REV.-A
I-3
12
14