Toshiba MM20E45, Техническое учебное пособие

Страница: 37 / 90

7-4
Ts is decided by the external time constant at pin 4, and is the
first delay value controlled by d.c. voltage of pin 3. This
phase value is not independent of hor period.
Tg is decided by capacitor at pin 6 and resistor at pin 9, and
is the second delay value that is controlled by d.c. voltage of
pin 5. This phase value is the function of hor period.
Tf is delay value of FBP which is decided by time constant
of pin 20.
SAW, which is AFC comparing waveform produced at pin
22, begins discharge at from edge of descent.
In Fig. 8, T
delay
means phase value from the front edge of hor
sync signal input at pin 1, to the center of FBP input to pin 18.
In figure, INT.SYNC is made by comparing triangle wave of
the second delay with a certain voltage. The pulse width of
INT. SYNC is always 1/10Th, independent of control voltage
at pins 3 and 5. Inside IC, the center of INT. SYNC and such
a point that 1/10Th passes from the start time of discharge
of SAW waveform, are controlled to be coincide together by
the AFC circuit.
The control voltage of pin 8 and the hor free-running frequency
fH are represented by the following expression.
Fh=(2/3) • 1/(11.5CR) • (V8+1)
Here; V8 : Control voltage of pin 8
C : External capacitor of pin 11
R : External resistor of pin 9
(7) Pin 7 is connected with capacitor which smooths AFC
comparing waveform.
In figure, Vsig is the same signal as the comparing waveform
made at pin 22.
(8) Pin 8 is control terminal of hor osc frequency of pin 11.
The range of control voltage is 0 to 2.5V. When this voltage
is 0V, hor osc frequency becomes the lowest frequency, and
when 2.5V, it becomes maximum.
(9) Pin 9 gives output of voltage which is added by 1V to the
voltage input at pin 8.
The current decided by external resistor flows through hor
osc circuit, second DELAY, and SAW generator to control
them. Variable resistor RH25 adjusts hor osc frequency.
7
5K
Vsig
100
4.7 F
Fig. 9
1.8K
8
Fig. 10
2K
666
3K
RH25
RGB
ADJ.
2K
9
Fig. 11
(10) Pin 10 is filter terminal of AFC.
The time constant of this filter affects hor jitter. The pull-in
range of AFC is ±4.7%, and does not depend on the constant
of the filter so much.
7.5K
7.5K
25K
0.027
10
2.2 F
1K
2.2 F
Fig. 12