TEA2029 STMICROELECTRONICS [STMicroelectronics], TEA2029 Datasheet - Page 43

• Manufacturer Part Number: TEA2029
• Description: APPLICATION NOTE
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

The bias voltage ”V
winding of EHT transformer. The parabolic effect is
due to the integration of frame saw-tooth by the
filtering capacitor ”C1”.
Where :
- I
- T : 20ms
- C1 = 1000 F
VIII.5 - Frame Flyback
During flyback, due to the loop time constant, the
frame yoke current cannot be locked onto the
reference saw-tooth. Thus the output of amplifier
”A” will remain high and the thyristor is blocked.
The scanning current will begin flowing through
diode ”D”. As a consequence, the capacitor ”C”
starts charging up to the flyback voltage. The thyris-
tor is triggered as soon as the yoke current reaches
the maximum positive value.
EHT transformer winding (see Figure 88)
(for 90
Figure 88
VIII.6 - Feed-back Circuit
VIII.6.1 - Frame power in quasi-bridge configu-
ration (see Figure 89)
This stage measures the frame scanning current in
differential mode and compares it to the reference
saw-tooth on Pin 3.
-
-
-
Y
V
I
L = 500 H
YOKE
: Peak-to-peak yoke current = 380mA
LF
o
= 210V
= 380mA
tube : Yoke
PP
DVB =
PP
V
B
LF
” is supplied by the secondary
8 C1
I
Y
L
L = 120mH, r
I
I
DIODE
THYRISTOR
-
-
-
C = 0.47 F
V
Flyback duration = 1ms
T
LF
= 0.95V
9.2 I
C
Y(PP)
Y
= 60 )
Load
Yoke
r
V
Y
B
pp
The overall configuration is built around two sym-
metrical networks :
- ”R
- ”R’
A.C. gain : G =
where :
- I
- V
-
VIII.6.1.1 - Choice of ”R” value
The saw-tooth generator output is an emitter fol-
lower stage. Pin 3 output current must therefore be
always negative.
Where :
- V
- V
Example :
- R1 = 22k
- V
- V
VIII.6.1.2 - Influence of R3 value
R
voltage should be lower than 5.5V so as to enable
the frame to function upon initial start-up at
V
If the bias voltage is higher than this 5.5V level, the
d.c. open-loop gain will fall thereby rendering the
system more sensitive to d.c. drift.
Satisfactory results are obtained at V
falling within 4V to 5V range.
Where : V
Capacitor ”C” connected between Pins 1 and 2
determines the system stability. Its value must be
appropriately calculated as a function of ”R
and R
component.
TEA2028 - TEA2029 APPLICATION NOTE
CC
saw-tooth voltage
the d.c. shift control.
3
Y
IN
BIAS
IN(MIN)
BIAS
IN(Min.)
sets the bias voltage for Pins 1 and 2. This
1
: Peak-to-peak Yoke Current
R3 = R2
1
= 6V.
, R
: Peak-to-peak saw-tooth voltage (Pin 3)
, R’
[0,1] : amplitude adjustment
3
” values so as to reject the line frequency
: Bias voltage for Pins 1 and 2
= 5V
2
2
, R
: Saw-tooth voltage low level
, R’
= 1.26V
IN(MEAN
3
R << R1
3
” network : determines the dynamic
V
” network : sets the bias voltage and
B
R
R
[V
) : saw-tooth mean value (Pin 3)
2
1
IN
=
MEAN
V
I
V
Y
IN
BIAS
R
V
V
IN Min.
G]
BIAS
R
10
R
V
1
M
IN
V
Min.
BIAS
BIAS
[1
values
G]
1
43/46
, R
2