Over Voltage Protection; Over Current Protection - NEC MultiSync LCD2080UX -BKA Service Manual

2.9.7 Over Voltage Protection

If some failure occurs and the output voltage of the secondary windings of T901 increase, the voltage of the
auxiliary winding of T901 also will increase proportionally. The protection circuit built into IC901 operates
when the voltage of 1pin of IC901 rises to about 28V,and Q911 is turn on.
Then the voltage of IC901 pin7 reaches over 8.8V and the oscillation is stopped.
IC901
VCC 1
MultFP
7
GND
6

2.9.8 Over Current Protection

If some failure occurs and the total power of secondary outputs increase, the peak voltage of 4pin of IC901
increase proportionally. And when the peak voltage of 4pin reaches 0.62V, IC901 decrease on period duty
cycle of Q901 , and limits the transmission of the electric power. IC901 stops oscillating.
C906
GND
C906
Q911
R922
C9X2
R9X4
(Fig. 2.9.7) Over Voltage Protection
0.62V
IC901
OCP
4
C913
6
(Fig. 2.9.8) Over Current Protection
C920 R920
ZD920
R636
FROM IC901 PIN2
DRIVE CIRCUIT
R917
7-15
D915
D911
R911
C911 C910
T901
Q901
R909
T901