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0
i
L
i
K
V
C
V
P
V
L
t
LF
E
0
i
C
End of
Trace
Begining of
Trace
if K remains
open
t3
t4
t1
t2
0
0
0
E
2
Figure47
In practice, the power switch ”K” is built by a
combinationof ”HighVoltageSwitchingTransistor”
and ”FastRecovery Diode”.
If considered in average value, it is seen that the
voltageacrosscapacitor”CS” isalmostequalto the
source voltage ”E”. The saw-tooth current through
thiscapacitorwill produceaparabolicripplearound
”E”, whichwillthus modifythe equivalentsourceof
the line yoke and induce a modified current of ”S”
shape within the yoke. This ”S” current is used to
producea linear picture asa functionof thepicture
tubegeometry.
The basic arrangement can be reconstructed by
assuming that the equivalent inductor ”L” is the
transformer ”L
P
” and line yoke inductors put in
parallel (since VC
S(AV
) = E).
The output Pin 10 of TEA2028 is applied to a
matching stage called ”line driver” the output of
which drives the power transistor ”T
r
”. The match-
ing stage is necessaryfor optimized base drive.
Atmiddle oftrace, the transistorentersinto satura-
tionand itscurrent riseslinearly.V
10
will thenissue
a control signal to turn the transistor off. The tran-
sistor will be in fact turned-offafter a delay interval
”t
S
” (storagetime) varyingfrom 2to 8
μ
s depending
on application. The system will then enter into
oscillationduringits half-periodtherebygenerating
the line flyback. At theend of flyback time, the line
yoke current is negative while the voltage across
capacitor”C” hasfallentozero.Theenergytransfer
automatically takes place by the recovery diode
duringthe first portion of trace time.
Also, it is clear that the line scanning phase with
respectto videosignal is determinedby the rising-
edge of Pin10 outputsignal.
10
12
Line Flyback
Input
L
R
Coupling
Capacitor
T
DRIVER
+12V
Tr
I
Tr
I
C
I
D
D
V
EHT (anode)
[15 to 25kV]
Miscellaneous Power Supplies
Line Flyback
(Pin 12, TEA2028B)
C
C
5
V
C(5)
I
Y
Line Yoke
EHT
TRANSFORMER
E
(regulated by SMPS)
L
P
TEA2028B
2
Figure 48 :
SimplifiedDiagram of the Horizontal DeflectionStage
TEA2028 - TEA2029APPLICATIONNOTE
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