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1 . MAIN POWER SUPPLY CIRCUIT
1-1. Description
Power supply circuit employs APS-115. This power
supply boosts up at boost-up-converter just after bridge-
rectifying AC input voltage, supplies the voltage
smoothed to DC 350V to the lamp power. Then current
resonance DC-DC converter which uses the DC 350V as
an input converts the voltage and supplies S6V, +6V,
+3.3V, +10V, +13V, +16.8V and –7V.
The boost-up-converter control IC, IC301, stabilizes AC
rectified voltage to DC 350V. The current resonance DC-
DC converter, IC303, turns FET Q102 and Q103 "ON/
OFF" alternately converts the voltage to secondary side
through the converter transformer T101. At this time, the
voltage of S6V at the secondary side is detected by
IC402, the negative feedback to IC303 is carried out at
photo coupler PH301 and then the voltage is stabilized.
Other outputs are determined by the turn ratio of second-
ary side of T101, and the voltage rectified, smoothed, but
not stabilized are stabilized through the series regulator.
(+10V is stabilized at IC203, +13V at IC202, +16.8V at
IC201 and +3.3V at IC204.)
The voltage rectified and smoothed by D108 and C124 at
primary winding of T101 is supplied as a power supply
voltage of IC301, IC302 and IC303 on primary side ICs.
Therefore, when the current resonance DC-DC converter
stops to oscillate, the power supply is not supplied to
each IC so that the boost-up-converter stops to operate.
1-2. Output Control
The power supply circuit has a function to turn on/off the
secondary output lines other than S6V by the external
control. The control by pin 21 of connector CN201 turns
on/off each output of +6V, +3.3V, +10V, +13V, +16.8V
and the pin 23 turns on/off the output of +13V. In both
cases, each of the control pins turns off at low and on at
high. When the control pin develops low, the voltage of
approx. 6V is added to Q201 base, IC201, IC203 and pin
4 of IC202 through R419 and R420 respectively, since
the transistors Q403 and Q402 turn off. In this case,
Q202, IC203, IC201 and IC202 turn off, the outputs of
+6V, +3.3V, +10V, +13V and +16.8V are not developed.
When the control pin develops high, the transistor Q202,
IC203, IC201 and IC202 turn on, so no voltage is added
to the base of Q201, IC201, IC203 and pin 4 of IC202,
described above, and the outputs of +6V, +3.3V, +10V,
+13V and +16.8V are developed.
1-3. Over-voltage Protection
When the negative feedback circuit of current resonance
DC-DC converter is shut down, the secondary side
voltage control is unable to operate, the voltage begins to
develop high without any restriction. At this time, when
the voltage of S6V and +6V exceeds 8.5V, the base of
transistor Q401 is biased through the zener diode D403,
and turns on, and then the voltage higher than 7V is
added to pin 6 of IC303 through the photo coupler
PH307. When the voltage higher than 7V is added to pin
6, IC303 is latched, all outputs are shut down and the
status is kept continuously. ( Boost-up-converter stops
simultaneously, too.)
When releasing the latch operation, stop to supply the
mains power supply and then re-supply the mains power
after more than approx. 120 seconds.
1-1
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