4.0 DESCRIPTION OF CIRCUIT CFA1797B
4.0 DESCRIPTION OF CIRCUIT
1. Power supply circuit
T e AC voltage input connected to EMI circuit
and rectifier circuit. R102, R112 and Switc
(SW101) will provide DC voltage to IC101,
w en switc on. W ile IC101 works normal,
T e IC101 will Auto-detect output voltage of
power supply from Pin2 and correct t e duty
cycle of Pin6 output pulse to compensate t e
variation of output voltage.
T e output of IC101 Pin6 connected to power
MOSEFET to drive t e power transformer
T101. W en power MOSFET is on, t e energy
stored in t e primary winding of T101. Once
MOSEFET is off, t e energy transfer to t e
secondary and c arges t e output capacitor to
get t e stable DC voltage.
2. Oscillation circuit
T e functions H-size, H-p ase, V-size, V-
center, Side-pin, Parallel….are designed inside
into IC301. T e Pin25 is X-RAY protect input.
W en H.V output circuit is abnormal (H.V too
ig ) t e X-RAY protect circuit will s ut off t e
orizontal output, H.V. also will be s ut down.
T e Pin28 is B+ control driver output. T e
Pin26 is orizontal square wave output drives
orizontal output. T e Pin24 is parabolic
output. T e Pin23 is vertical output. T e Pin1
& pin2 are H-SYNC & V-SYNC input. T e Pin3
is vertical blanking output. T e Pin 20, 22 for
vertical oscillator. T e Pin 6, 8 for orizontal
oscillator.
3. Vertical output circuit
T e Pin23 of IC301 is vertical sync output
connected to IC201 (Amplifier), Pin5 of IC201
is vertical amplifier output drives t e vertical
deflection directly.
4. Horizontal output circuit
T e DC-DC is to generate a DC voltage (B+)
for orizontal output circuit. T e CPU (IC501)
controls t e H. size adjustment function of
IC301 via t e I2C Bus. T e output of IC301
(Pin6) connected to gate of Q311 to make t e
Q311 switc ing. W en Q311 is ON, t e
energy stored in T304 and t e energy released
via D313 w en Q311 turned OFF. T e B+
applied to Horizontal Yoke and supply t e
power for orizontal deflection. T e more t e
B+ will get t e bigger t e orizontal size.
5. Micon circuit
T e IC501 (CPU) will detect polarity and
frequency of input H.V. Sync. T e CPU will
determine t e mode of input timing (preset or
users mode) and load mode data from IC502
(EEPROM). T e outputs of IC501 were
connected to ot er function circuit (IE. H-size,
H-p ase, V-size, and V-center…). Also, t e
user can adjust picture from keyboard and t e
data will be saved into IC502 automatically.
For t e O.S.D. mode, w en O.S.D. manual is
active CPU will inform t e O.S.D IC (IC603) to
send O.S.D BLK signal to blank t e video
signal from VGA card, and t e O.S.D. IC will
send O.S.D. R.G.B. Video signal to s ow t e
O.S.D. manual on screen.
6. H.V. regulation circuit
T e IC401 is a P.W.M IC; Pin6 is P.W.M
output, w ic connected to Q407, Q409. T e
Q402 is H.V. output switc ing transistor. Q401
and D401 are damper device provide t e pat
of damper current. Q421 is a feedback voltage
from FBT Pin13 connected to PIN2 (IC401)
and correct t e duty cycle of PIN6 output pulse.
7. Video output circuit
Video circuit consists of video preamplifier
IC601 and output cascade amplifier IC604.
IC601 is a video processing IC equipped wit
t ree DC amplifiers to pre-amplify R.G.B.
signals from 0.7V to 4.2V.
T e R.G.B. GAIN & BIAS control signal are
from IC501 via I2C-bus to DAC IC601. T e
IC601 control to video gain. T e output of pin
24, 25, 26 are connected to BIAS circuit of
eac R.G.B. signal’s amplification and t us
ac ieve a well balance able w ite picture.
T e O.S.D. R.G.B. (Pin4, 9,13 of IC601) is t e
input of O.S.D. Video signal. T e IC604 is
R.G.B. drive to capable of driving CRT.
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