ViewSonic E95 - Page 51

41 circui iptior
4.5.6 PARALLEL and PIN-BALANCE CONTROL
Parallel CKT is superimposed the vertical sawtooth current inside of IC401 the waveform amplitude
is adjust by IC301 SCL SDA control IC401 pin18 pin 19.
Pin-balance CKT is superimposed the vertical parabolic current inside of IC401 the waveform
amplitude is adjusted by IC301.
4.5.7 X-RAY-RADIATION PROTECTION
The X-Ray-radiation protection circuit usually uses in the monitor latching type circuit. Therefore,
should a fault occur which would activate the X-ray protect circuit, Should a fault occur which would
cause the high voltage to increase above a predetermined level, the positive pulse at pin7 of the FBT (T404)
would go more positive. This will increase the voltage applied to ZD405 to exceed its breakdown voltage
for a certain time. An latch circuit Q434 Q435 switches the IC404 pin1 into protection mode. Shutting
down the IC404 and Q437.
NOTE: The X-RAY-Radiation protection circuit used in this monitor is a latching type the monitor
will shut down and continue until turn-off the monitor by power switch.
4.5.8 Vertical Deflection (IC501)
Vertical deflection function is operated in the IC401, IC501 that mainly contains the oscillator, ramp
generator, and power output amplifier and flyback generator. Vertical oscillator is obtained amplifier by
means of and integrator driven by oscillation circuit that is determined by C402, C403 and R406. The
vertical sync signal is applied to the pinl4 of IC401. Once the sync signal synchronized a clock pulse is
generated inside this chip. The clock pulse is just as a sync input of ramp generator. A liner voltage ramp is
produced at pin12,13 of IC401, and is couple to IC501 pin1,7 for vertical output amplitude Vertical output
amplitude is controlled by R502/R505, IC401 inside parameter and IC301 Vert. size DAC.
The CKT of the TDA8172 provides a high CMRR current driven differential input (pin1,7), the
output stages (pin3,5) in a full bridge configuration, a flyback generator, a protection CKT for the output
stage and a guard CKT.
The pin5 is the output of the power amplifier and it drives the yoke by a current driven in opposite
phase current ramp. Pin2 is the supply voltage 15VDC, Pin4 is supply voltage —-15VDC, the pin3 is the
feedback pulse feedback to pin6.
Vertical frequency is 100~180Hz, Q401 off so vertical free run is only determined by C402. If
vertical frequency is 50~100Hz, Q401 on so vertical free run is determined by C402 + C403. Total vertical
frequency range is from 50Hz to 180Hz.
Vertical centering is controlled by changing the DC voltage at vertical output that is caused from the
DC shift of IC401 pin13, and that can be adjusted by DAC control of IC301.
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