Service manual

Page 30
MODELS: LT-3280D/LT-3780D
3.3.
3.3.
3.
Power circuit Power circuit
Power circuit Power circuit
Power circuit
For power supply of LT-3280D and LT-3780D, there are the power supply of “always on” and “ON/OFF” with a
control signal.(Refer to BLOCK POWER.pdf)
(O)IC9A1, IC901(Only 32”) :
Power supply control IC(power factor correction) (FA5500/FA5501 : FUJI)
This IC are control IC for a power factor correction converter using critical conduction mode of
operation. This IC performs a power factor correction by conversion the current waveform from
triangle waveform to sine waveform. This IC and circuit is the same as LT-4260.
(P)IC9A2, IC902(Only 32”) : Power supply voltage control IC (F9222 : FUJI)
This IC controls the power supply voltage by switching about 75KHz.
This IC has MOSFET inside IC, keep switching on and off, and controls its duty to be stable output
voltage. . This IC and circuit is the same as LT-4260.
(Q)IC920(Only 37”) : Power supply voltage control IC (STR-G9628 : SANKEN)
This IC controls the power supply voltage by switching above 50kHz.
This IC has MOSFET inside IC, keep switching on and off, and controls its frequency to be stable output
voltage. And the duty is determined by input AC power voltage.
PCB Power
source
si
g
nal
Voltage
[V ]
“always on”
or “ON/OFF”
Control
signal
Output
IC
Note
POWER-
SUB1
120V 120V ON/OFF Psave1 For inverter.
Onl
y
37”
POWER-
SUB2
24V 24 ON/OFF Psave1 For inverter.
Onl
y
32”
24V 24 always on -For MAIN
18V 18 ON/OFF Psave4 IC9B5 Only 37”
P5V 5 ON/OFF Psave4 IC9B6 Only 32”
S8V 8 always on - IC9B4
S5V 5 always on - IC9B7
S3.3V 3.3 always on -IC830
AMPVC
C
17 ON/OFF Psave3 IC9B3
4.5V 4.5 ON/OFF Psave2 IC9B2
A3.3V 3.3 ON/OFF Psave2 IC9000
D3.3V 3.3 ON/OFF Psave2 IC9010
AD3.3V 3.3 ON/OFF Psave2 IC9020
D2.5V 2.5 ON/OFF Psave2.5 IC9030
A1.8V 1.8 ON/OFF Psave2.5 IC9040
POWER
MAIN