TEA2028 datasheet(24/47 Pages) STMICROELECTRONICS

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i L

i K

t LF

i C

End of

Trace

Begining of

Trace

if K remains

open

Figure 47

In practice, the power switch ”K” is built by a

combination of ”High Voltage Switching Transistor”

and ”Fast Recovery Diode”.

If considered in average value, it is seen that the

voltage across capacitor”CS” is almost equalto the

source voltage ”E”. The saw-tooth current through

this capacitor will produce a parabolicripple around

”E”, which will thus modify the equivalent source of

the line yoke and induce a modified current of ”S”

shape within the yoke. This ”S” current is used to

produce a linear picture as a function of the picture

tube geometry.

The basic arrangement can be reconstructed by

assuming that the equivalent inductor ”L” is the

transformer ”LP” 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 ”Tr”. The match-

ing stage is necessary for optimized base drive.

At middle of trace, the transistor enters into satura-

tion and its current rises linearly. V10 will then issue

a control signal to turn the transistor off. The tran-

sistor will be in fact turned-off after a delay interval

”tS” (storage time) varying from 2 to 8

µs depending

on application. The system will then enter into

oscillation during its half-period thereby generating

the line flyback. At the end of flyback time, the line

yoke current is negative while the voltage across

capacitor”C” has fallen to zero. The energy transfer

automatically takes place by the recovery diode

during the first portion of trace time.

Also, it is clear that the line scanning phase with

respect to video signal is determined by the rising-

edge of Pin 10 output signal.

Li ne Flyba ck

Input

Coup li ng

Ca pacitor

TDRIVER

+1 2V

ITr

I C

VEHT (anode)

[15 to 25kV]

Miscellaneous Power Supplies

Line Flyback

(Pin 12, TEA2028B)

CC 5

VC(5)

Line Yoke

EHT

TRANSFORMER

(regulated by SMPS)

L P

TEA2028B

Figure 48 : Simplified Diagram of the Horizontal Deflection Stage

TEA2028 - TEA2029 APPLICATION NOTE

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