Epson LQ-2550 Technical Manual page 75

After the power is turned on, as the voltage across C 12 rises, the current is stabilized. Therefore, after
the power switch is turned on, resistor R9 is inserted in series between smoothing capacitor C 12 and
the input line to limit the surge current until the voltage across C 12 is stabilized. When 120 VAC is
applied, the voltage across C 12 reaches about 170 V. In this circuit, the surge current is limited to
approx. 17 [A] or less (170/R9 = 17 [A]).
When C 12 is fully charged, R9 is shorted to prevent it from wasting energy as heat. It is shorted by
TRIAC TY 1. When FET Q3 is turned on, voltage is induced by coil T314-13 at the primary side in coil T314-13
at the secondaw side of transformer T3, and the line between T1 and T2 is shorted upon receiving
2.2.4 Main Switching Circuit 1
Figure 2-22 shows main switching circuit 1.
Is
R2
SURGE CURRENT$
INPUT VOLTAGE
Figure 2-21. Surge Current
I
D2
E
A
cl 1
- — — .-
R5
I
D1
R 1 :
Figure 2-22. Main Switching Circuit 1
v
T1
7
2-28
To the
circuits
"at the secondary
side
L
12