Power Sw Circuit; Switching Regulator Circuit; Rectifying Circuit - NEC MultiSync LCD2080UX -BKA Service Manual

2.8 POWER SW Circuit

When the front POWER SW is pressed in the state that the vacation SW is turned ON and the LED is unlit,
the POW_SW line is turned to the GND level and Q151 is turned on to supply a power of 5Vdc. The power
circuit of 5Vdc is connected to the ON/OFF terminal of IC221. When IC221 is started, the power is fed to
the MPU. The POW_SW line is connected also to the base of Q156, and therefore both Q156 and Q157
are turned on. The Q157 collector output circuit of "SWI" is connected to the MPU. When "SWI: L" is
detected after the MPU has canceled the reset state, the condition of the front POWER SW pressed ON is
identified.
If the front POWER SW is pressed ON in the state that the LED is lighting, Q156 and Q157 are turned on in
the same manner as described above. When Q157 is turned on, SWI is turned to the L level. When the
MPU identifies the condition of "SWI: L → H" in the state of normal operation, image blanking, panel power
supply OFF, and other processes are carried out. Since then, the output port signal of "SWO" is set at the H
level. When "SWO" attains the H level, Q154 is turned on and Q153 is turned off. Therefore, Q151 is turned
off to stop the operation of this unit.

2.9 SWITCHING REGULATOR CIRCUIT

2.9.1 Rectifying Circuit

AC input is rectified by D901 and supplied to the power factor collector circuit.
AC
AC
POWER FACTOR
COLLECTOR
D901
CIRCUIT
(Fig. 2.9.1) Rectifying Circuit
7-10
C906
MAIN SW. REG
CONVERTER
CIRCUIT