Circuit Description; Power Block; Outline; Rectifying Circuit - NEC FP1355 Service Manual

1.

Circuit description

1.1

Power block

1.1.1

Outline

(1) The power block is compatible with 100 to 120VAC/220 to 240VAC(50/60Hz).
(2) The active filter circuit is adopted to suppress the higher harmonic current and improve
the power factor.
(3) The circuit that supplies the electric power to the secondary side is divided into two
circuits that are respectively called the main power and sub power.
Though both main and sub circuits supply the power to the secondary side in the normal
operation mode, the power is supplied from the sub power only in the power save mode
since the main power is stopped.
The main power is the configuration used the flyback converter type switching control IC of
the simulative resonant operation. Moreover, the sub power is the configuration used PRC
(OFF width fix) control IC.
(4) The output on the secondary side is shown in Table 1.
(Refer to the power system diagram1-3 in Pages 1-3, 1-4 and 1-5.)
Power block Output voltage
Main power +215V
side
+80V
+15V
-15V
+12V
+7.5V
+5V
Sub power
side
P-OFF+5V
1.1.2

Rectifying circuit

(1) The AC input voltage is rectified in the full wave mode with the diode bridge in D901.
(2) In the higher harmonic circuit of the section 1.1.4, the AC input current becomes the sine
wave form in the same phase with the AC input voltage waveform, but the interference is
given to other peripheral devices since the noise of the switching current appears on the
input side owing to the switching waveform. Therefore, L902 and C906 are inserted to
suppress the noise that is caused by the switching current.
1.1.3

Surge current suppression

(1) TH901 (thermistor) suppresses the rush current that flows when the power switch is turned
ON. Moreover, D933 is added to protect D902 from the rush current.
Application
H. deflection circuit, Video cut off circuit
Video circuit, DBF circuit, High voltage circuit
H/V deflection circuit, etc.
H/V deflection circuit, etc.
Video circuit, H. deflection circuit, etc.
Heater
MPU, etc.
Video circuit, etc.
Table 1
1 - 1
When power save
OFF
OFF
OFF
OFF
OFF
OFF
ON
OFF