ITT - Index of

TBA940
HORIZONTAL DEFLECTION PROCESSOR
FOR THYRISTOR (SCR) OUTPUT STAGES
The switching stage has an auxiliary function.
When the two signals supplied by the. sync
separator and the phase control circuit respectively
are in synchronism a saturated transistor
is paralleled to the integrated 2kO resistor
at terminal 9 and ground. Thus the time
constant of the filter network at terminal 4 increases
and consequently reduces the pull-in
range of the phase comparator circuit for the
synchronized state to approximately 50Hz.
This arrangement ensures distortion-free operation.
For video recording operation this automatic
switchover can be blocked by a positive current
fed into terminal 8, e.g. via a resistor
connected to pin 3. It can also be useful to
connect a resistor of about 6800 or 1 ko between
pin 9 and ground. The capacitor at terminal
4 may be lowered, e.g. toO.1p.F. These
alterations do not significantly influence the
normal operation of the IC and thus do not
need to be switched out, when changing from
VTR to TV or vice versa.
The short circuit proof output stage delivers
at terminal 2 output pulses of duration and
polarity suitable for driving the output driver
stage. If the supply voltage goes off (e.g. by
switching off the A.C. voltage) a built-in protection
circuft takes care to provide defined
line frequency pulses down to V,,=4V and
shuts off when Va gets below 4V preventing
pulses of undefined duration and frequency.
Vice ver.sa if the supply voltage rises, defined
pulses in duration and frequency will appear
at the output terminal when Va reaches 4.5V.
In the range between Va=4.5V and full supply
voltage the shape and frequency of the output
pulse are nearly constant.
Fig. 3 - Phase relations of the TBA940. The
line flyback pulse overlaps the video signal
sync pulse on both edges.
Flyback
pull.
(Video)
BAS Signa I
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10
Output
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Fig 4: Operating circuit
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Input signal ~-
(Video) ~ 1
Rv
7
3
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TBA940
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B1120
BC327
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Phase'
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8-24