9-12
The reference voltage is supplied to pin 3, and this voltage is
produced from 4 kinds of voltages. From pin 8 of IC302,
voltage for size adjustment as a main is supplied. This
voltage is provided from pin 11 of ICX00, by operation that
Micom ICA01 transmits data through T-Bus line to DAC
ICX00. Accordingly adjustment can be done by remote unit,
and only in RGB mode user can control by key of remote unit
and of TV set.
From pin 14 of ICK09, correction voltage of pincushion
distortion is added. This voltage is also taken out from pin 4
of IC302, by operation that Micom ICA01 transmits data
through I
2
C-Bus line to IC302 (TA8859AP).
From pin 7 of ICK02, in RGB mode output voltage of F/V
convert circuit is applied , and in TV mode adjusting voltage
of hor osc frequency is applied. By these operation, size is
automatically corrected to some extent, corresponding to
frequency of input signal.
Further, from IC407 through CK23, voltage which is obtained
by detecting voltage ripple of high voltage, is applied. The
reason to apply this, is to correct distortion of picture caused
by variation of high voltage.
In high voltage circuit, method which stabilizes high voltage
is employed, but intentionally the regulation is not so
effectively performed as to eliminate voltage ripple perfectly.
If the perfect regulation is done, power consumption supplied
to FBT increases so much when white peak current flows,
and big burden is applied to chopper regulator in control
operation. For designing of compact circuit, the distortion is
corrected with less extent of regulation, and picture quality
is kept. QK10 is a transistor which changes correction value,
and is turned on in the mode that frequency is 28kHz or less
to reduce correction value.
QH26 changes voltage dividing ratio so that the size adjusting
voltage applied from pin 8 of ICK09 is not out of standard,
and is turned on in 28 kHz or less of frequency.
The trigger pulse which is applied to timer IC ICK01
(TA7555P), is produced from output pulse of ICH08
(LA7860) of hor osc circuit. By synchronizing chopper
regulator to hor deflection circuit, prevention of interference
like hor jitter is aimed.
Vcc
8
7
6
5
1
23
4
R
COMP1
COMP2
SQ
V
REF
DISCHARGE
THRESHOLD CONTROL VOLTAGE
GND
TRIGGER OUTPU
RESET
R
R
R
Fig. 14
Next, operation of PWM circuit using timer IC, is explained.
First, IC block diagram is shown in Fig.14.
To pin 2 of timer IC, trigger pulse is applied, and to pin 4 reset
pulse is applied. And to pin 5, control voltage from pin 1 of
error amp ICK02 is applied. In this way, adjustment of size
and correction of distortion are done.
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