1 - 3
1.2.2
Switching circuit operation
When actually changing over, if the voltage Vth (1) of the pseudo-signal applied on the HIC pin
OCP/FB terminal is nearly equal to 0.76VMIN or more or less than the threshold voltage Vth
(2) 1.3V, the internal Comp 1 operates, and PRC operation with a fixed OFF interval takes
place at TOFF 50
µ
S.
When this voltage is more than the threshold voltage Vth (2) 1.5V or more (Max. 6V), the
internal Comp 2 operates. The OFF time generated by the internal transmitter changes at
approx. 1
µ
S (Max). MOSFET remains OFF while the voltage is higher than the threshold
voltage Vth (1).
Pseudo-resonance operation refers to matching the timing for turning this MOSFET ON with
the bottom point of the voltage resonance after the transformer has discharged the energy, and
with a cycle one-half of the resonance frequency. When the voltage resonance capacitor C906
is connected between the drain and ground, and the delay circuit R907, R909, C914 or D902 is
connected between the auxiliary coil T
-
and pin
OCP/FB terminal, the flyback voltage
generated from the auxiliary coil when MOSFET is OFF causes the pseudo-resonance signal to
operate the IC internal Comp 1 and Comp 2, and starts pseudo-resonance operation.
Even when discharge of the transformer energy has finished with the delay circuit, the pseudo-
resonance signal will not lower to the pin
terminal immediately. This is because the charge
at C909 and C914 rises above the threshold Vth (1) or less for a set time after the charge is
discharged by the composite impedance of the IC internal active lowpass filter and R905.
<Waveform at switching>
IC901 pin
waveform
At standby
When normal
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...
Page 90: ...SCHEMATIC DIAGRAM PWB MAIN INPUT LCD1550X...
Page 91: ...SCHEMATIC DIAGRAM PWB MAIN SYNC LCD1550X...
Page 92: ...SCHEMATIC DIAGRAM PWB MAIN TMDS LCD1550X...
Page 96: ...SCHEMATIC DIAGRAM PWB MAIN ASIC LCD1550X...
Page 97: ...SCHEMATIC DIAGRAM INVERTER LCD1550X 1ch Q701 B 2ch Q702 B...
Page 98: ...SCHEMATIC DIAGRAM PWB SW LCD1550X...
Page 100: ...SCHEMATIC DIAGRAM POWER LCD1550X...
Page 101: ...SCHEMATIC DIAGRAM PWB MAIN POWER LCD1550X...
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...
Page 106: ...SCHEMATIC DIAGRAM PWB MAIN ASIC LCD1550X...
Page 107: ...SCHEMATIC DIAGRAM INVERTER LCD1550X...
Page 108: ...SCHEMATIC DIAGRAM PWB SW LCD1550X...
Page 127: ...16 Document No VSPF A028 Bave Average brightness of 1 to 9 10 50 90 90 10 50 5 1 2 3 6 9 8 7 4...
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