1 - 6
1.2.4
Protection circuit
A fuse is inserted in the 12V line (F910, F911) as an overcurrent protection and as a circuit
that maintains the oscillator output at the LOW level and stops the power circuit operation
when the overvoltage protection (OVP) circuit or overheat protection (TSD) circuit operate.
1.2.4.1.
Latch circuit
This circuit maintains the oscillator output at the LOW level and stops the power circuit opera-
tion when the overvoltage protection (OVP) circuit or overheat protection (TSD) circuit operate.
The latch circuit holding current is 70
µ
A max. (Ta = 25˚C) when the voltage of pin
is 10.5V.
By considering that this increases lightly at high temperatures and by passing a current of
140
µ
A or more to the pin
from the starting resistor, the power circuit will maintain the
stopped state. A delay time is provided with C2 in the hybrid IC to prevent malfunctioning by
noise, etc. If the OVP or TSD circuit operation continues for approx. 10
µ
sec or more, the
latch circuit will operate.
Note that even if the latch circuit operates, the constant-voltage power (Reg) circuit is function-
ing in the control circuit, and the circuit current is high. Thus, the voltage of pin
will drop
suddenly. When the voltage of pin
drops to below the operation stop voltage (10.1V (typ.)),
the circuit current will drop to 70
µ
A (Ta = 25˚C) or less, so the voltage of pin
will start
rising.
When the operation start voltage (17.6V (typ.)) is reached, the circuit current will start to in-
crease again, so the voltage of pin
will drop suddenly. Thus, when the latch circuit is oper-
ating, the voltage of pin
will rise and lower between 10.1V (typ.) and 17.6V (typ.) and pre-
vent the voltage of pin
from rising higher. An example of the voltage of pin
waveform
during latch circuit operation is shown in the figure below. The latch circuit is canceled by
lowering the voltage of pin
to less than 7.9V, and generally, it is restarted by turning the AC
power OFF and ON.
1.2.4.2
Overheat protection circuit
This circuit operates the latch circuit when the hybrid IC's frame temperature exceeds 135˚C
(MIN). The temperature is actually detected by the control circuit element. Since MOSFET
and the control circuit element are on the same frame, this will also function when MOSFET
overheats.
4
(TYP)
(TYP)
Example of waveform of pin at latch circuit operation
Summary of Contents for NEC MultiSync LCD1550X LCD1550X LCD1550X
Page 88: ...SCHEMATIC DIAGRAM POWER LCD1550X Normal Power Save 1ch Pin 4 2ch Pin 1 3ch Pin 2 4ch Pin 5...
Page 89: ...SCHEMATIC DIAGRAM PWB MAIN POWER LCD1550X...
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Page 91: ...SCHEMATIC DIAGRAM PWB MAIN SYNC LCD1550X...
Page 92: ...SCHEMATIC DIAGRAM PWB MAIN TMDS LCD1550X...
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Page 97: ...SCHEMATIC DIAGRAM INVERTER LCD1550X 1ch Q701 B 2ch Q702 B...
Page 98: ...SCHEMATIC DIAGRAM PWB SW LCD1550X...
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Page 102: ...SCHEMATIC DIAGRAM PWB MAIN INPUT LCD1550X...
Page 103: ...SCHEMATIC DIAGRAM PWB MAIN SYNC LCD1550X...
Page 104: ...SCHEMATIC DIAGRAM PWB MAIN TMDS LCD1550X...
Page 105: ...SCHEMATIC DIAGRAM PWB MAIN MC LCD1550X...
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