TEA2029 STMICROELECTRONICS [STMicroelectronics], TEA2029 Datasheet - Page 33

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

- Full protection of the primary-connected transis-
- Can provide 1W to 7W, for TV standby mode
V.7.4 - Power supply soft-start
When the TV set is initially turned on, control pulses
are not yet available and consequently the control-
ler block on primary side will impose a low-power
transfer to the secondary winding. This power is
produced by an intermittent switching mode called
”Burst Mode”.
As soon as the V
6V level, line and SMPS outputs are enabled.Since
the filtering capactitors on secondary side cannot
charge up instantaneously, the voltage to be regu-
lated would not yet be at its nominal value. Without
conduction period limitation upon start-up, the de-
vice will set a maximum cycle of 28 s which will
result in a high current flow through the primary
winding and thus through the switching transistor
which will in turn activate the protection function
implemented on primary side.
Consequently, the primary controller block will be
inhibited and the set will not turn-on.
A start-up system has been implemented within
Figure 66
tor in case of short-circuit or open-load on secon-
dary terminals
operation (refer to TEA2164 application note).
PIN 8 SUPPLY
VOLTAGE (V)
PIN 15
VOLTAGE (V)
SMPS CONTROL
OUTPUT VOLTAGE
(PIN 7)
LINE OUTPUT
VOLTAGE (PIN 10)*
* Lin e output (Pin 10) an d Thyristo rco ntrol output (Pin 4) for TEA2029C
CC
supply to TEA2028B exceeds
3.5
6
6
V
V
C C
CC
12V
Soft-start area
TEA2028B to overcome this problem.
This soft start system, will upon initial start-up, use
the image of the falling voltage on Pin 15 to in-
crease progressively the conduction cycle. The
phase modulator ”M2” compares this voltage with
line saw-tooth voltage and delivers the correspond-
ing limitation cycle.
During supply voltage rising cycle [V
< 6V], the capacitor Pin 15 will charge up rapidly
while the voltage across it follows V
At V
internal current generator and the voltage across it
decays linearly.
At V
age), phase comparator ”M2” delivers a low con-
duction period which will gradually increase.
The conduction period (Pin 7) will rise until the
secondary voltage reaches the value set by poten-
tiometer ”P”. When this occurs, the loop is acti-
vated.
The Pin 15 discharge current value is 100 A for a
duration of 2 s line frequency.
Therefore I
Conduction period limitation voltage (Pin 15)
T
Active area
TEA2028 - TEA2029 APPLICATION NOTE
ON(LIM)
Regulated Mode
CC
15
= 56 s - 16 x V
3.5V (line saw-tooth peak-to-peak volt-
6V, the capacitor is discharged via an
D AV
100
5.5V
5.5V
15
64
2
(in s)
V
C C
3.1 A
CC
.
CC
t
t
t
t
(Pin 8)
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