Main Switching Circuit; Circuit Operation - Epson LQ-1050 Technical Manual

The voltage across C6 increases after the power is applied, and the current is accordingly stabilized.
Until the voltage across
capacitor C6. When 120 VAC is applied, the voltage across C6 increases to about 160 VDC. In this
the surge current is limited to around 23 A, based
After C6 is fully charged, resistor
TY 1 for this purpose, which shorts T1 to T2 by passing current
power is applied to coil 14-12 of transformer
voltage reaches 1.5 V,

2.2.4 Main Switching Circuit

This circuit uses a ringing choke converter
the merits of using fewer parts and a smaller transformer, and is often used when a smaller power supply
is required.

2.2.4.1 Circuit Operation

Figure 2-12 shows the main switching circuit. When the power is applied, drive current Is flows to the
base of switching transistor Q 1 via starting resistor R 14. Diodes D20, D21, D22 on the secondary side
of prevent current flow in the secondary side. Therefore, as shown in Figure 2-13, collector current
from reaches the same level of current which flows in the coils, and starts from O A so that a small
base current can switch Q 1 on.
an input voltage which induces voltages in windings
respectively).
releases current
and releases base current
as shown in the following formula:
Therefore, when collector current
and DC
amplification rate
and is insufficient because of carrier saturation so
and drops and base current runs out, and Q 1 is quickly switched off.
When Q 1 is switched off, the back electromotive force which has the opposite polarity from the previous
momentarily flows through the windings of the transformer. Since the amount of energy
to that stored in the transformer before Q 1 is turned off, P is:
L ,
=
SURGE
INPUT VOLTAGE
Fig. 2-11. Surge Current
becomes stable, the surge current is limited by a resistor in series with
is shorted to keep its temperature low. The circuit includes
flows to switch on TY 1.)
1 is turned on, the primary side of transformer
in the direction which causes the gate of the
in the direction which causes
=
increases as shown in Figure 2-14, the relationship between
(=
can be expressed by the
L, 2
ton)
I
'
A
POWER ON
so that a voltage is induced in coil 9-10. When this
AC input switching power circuit. This system has
and
1 to remain on. The value of
V
I N
R 4 + +
1 is turned off. As a
2 - 1 3
formula: 160 R 1 = 23.5 [A].
to the gate. (When C6 is charged,
(represented by
(Refer to 2.2.3.) to conduct,
= where
X
the
of
Liactance
Peak current of
receives
and
is constant
is fixed
at
equal
P [W] is