Epson LQ-2550 Technical Manual page 82

Figure 2-28 shows the +35 V supply circuit.
Current flowing in the direction shown by@ is applied to choke coil L4 and smoothing capacitors C31,
If the output voltage from the secondary side reaches the limit of the current limiting or voltage regulator
circuits in the latter stage of this circuit, transistors TR 1 and TR2 of IC2" turn off so that no current
flows to coil T2s-z. IG therefore stops flowing to coil T2M (Refer to Figure 2-27.), VG becomes O V, and
rectified by D 10-2, smoothed by C31, C32, and C33, and output.
When the current drops below the limit of the current limiting or voltage regulator circuits (after Q3
has turned off), TR1 and TR2 turn on again, and this sequence is repeated. Figure 2-29 shows the
waveforms at various points in main switching circuit 2.
In this way, the voltage output from this circuit is kept constant by controlling the ON/OFF time of Q3,
which is the different method employed in main switching circuit 1.
2-30,
T3
10
. 5
12
0
2. coil T2 5-8
Choke
6.
10-1
D
- - - - - - - - L4
1
#
D1O-2
,
1
'. - - - - - - - -
- -
Figure 2-28. +35 V Supply Circuit
of T2 Current
of T 3 C u r r e n t @
coil L4 Current ~'
1035
8. Output current
Figure 2-29. Main
the energy ~' accumulated in choke coil L4 is output
R42
I
—
O
Switching Circuit 2 Waveforms
2-35
REV.-A
7
10
G
H
1