H-Size Pwm Converter - Acer 7299sl Service Manual

2.1.11 H-size PWM Converter

IC304 constitutes a PWM comparator to compare east-west parabola signal with sawtooth
waveform signal and output a PWM pulse at pin6 of IC304 .
What is PWM ? PWM means pulse width modulation. Basically PWM function needs two signal :
one is modulation signal (high frequency), another is modulated signal (low frequency). Thus, east-west
parabola signal is modulated by sawtooth signal. After modulation, the PWM pulse is input to Q321
(PWM converter ) via Q319, Q320 drive circuit.
2.1.12 H-size output circuit
From
H-drive
Circuit
•
Conventional H-output circuit has a positive " collector pulse" from 0V up to 1200V.
•
Q321 forms PWM converter to accept PWM pulse and vary Q321 On/Off duty.
2.1.13 Top ringing eliminated circuit
L304, R363, C332 constitutes top ringing eliminated circuit to reduce ringing at top of picture.
2.1.14 H driver circuit
HDRV signal is come from IC304 pin7 and is driverd by Q308 and Q309, then goes into Q315 gate
terminate. Q315 constitutes an inverting stage and combines with T304 to form H-size drive circuit
which drives Q314.
R341 and C324 constitutes a snubber circuit to decrease the voltage at Vds of Q315, R344, R3802,
R345 and D307 set optimum base current of Q314 to get lowest power consumption. T304 is
proportional drive transformer which offers adequate base current of Q314 from low frequency mode to
high frequency mode.
2.1.15 Cs capacitor control circuit
Circuit Operation Theory
B+
+1200V
FBT
Lp
H-OUT
Damping
TR
Diode
FIGURE.11 Conventional H-size output circuit
API Confidential
No Copy/Reproduction Allowed
0V
H-DY
1
Cf
2
Cs
2-9