TDA8145_04 Datasheet, PDF (5/9 Pages) STMicroelectronics – TV EAST/WEST CORRECTION CIRCUIT FOR SQUARE TUBES

Figure 6. Application Circuit with Keystone Correction
Line Transformer
(L.T.)
TDA8145
Pin 1
Voltage
LM
L1
10mH
Pin-cushion
adjustment
R3 RT2
R1 = ^VFRAME
66µA_PP
4.7kΩ
5
47kΩ
7
R4
18kΩ
C1
47nF
V_FRAME
2
TDA8145
6
V_S
1
C2
100nF
3
4
8
RT1
Keystone 100kΩ
Adj.
R2
12kΩ
C3
4.7nF
D1
1N4148
Hfly
from L.T. _R5
1kΩ
RT3
H. Width
CIRCUIT OPERATION
(see the shematic diagram)
A differential amplifier OP1 is driven by a vertical
frequency sawtooth current of ± 33µA which is
produced via an external resistor fromthe saw-
tooth voltage. The non–inverting input of this am-
plifier is connected with a reference voltage
corresponding to the DC level of the sawtooth volt-
age. This DC voltage should be adjustable for the
keystone correction. The rectified output current of
this amplifier drives the parabola networkwhich
provides a parabolic output current.
This output current produces the corresponding
voltage due to the voltage drop across the external
resistor at pin 7.
If the input is overmodulated (> 40µA) the internal
current is limited to 40µA. This limitation can be
used for suppressing the parasitic parabolic cur-
rent generated during the flyback time of the frame
sawtooth.
A comparator OP2 is driven by the parabolic cur-
rent. The second input of the comparator is con-
nected with a horizontal frequency sawtooth
voltage the DC level of which can be changed by
the external circuitry for the adjustment of the pic-
ture width.
The horizontal frequency pulse–width modulated
output signal drives the final stage. It consists of a
class D push–pull output amplifier that drives, via
an external inductor, the diode modulator.
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