VIPER25 STMicroelectronics, VIPER25 Datasheet - Page 23

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VIPER25

Manufacturer Part Number
VIPER25
Description
VIPerPlus family: quasi-resonant high performance off line high voltage converter
Manufacturer
STMicroelectronics
Datasheet

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VIPER25
7.8
Double blanking time
The blanking time, T
value) and the higher one is 6,3 μs (typical value). The value is linked to the voltage V
sampled during the time T
relevant
< 1V or it has the higher value if is detected V
Figure 30 on page 23
The higher value of the blanking time is normally activated during the start-up phase or in
case of output short circuit; when the output voltage of the converter is quite lower than the
regulated value. In this condition can happens that during the demagnetization of the
transformer, the V
V
higher frequency and in continuous mode. This false trigger is inhibited by the selection of
the higher value of T
During the normal operation, in steady state condition, the voltage V
demagnetization is higher than 1V and the selected T
Figure 30
Figure 30. Double T
(pin 3)
0.6V
T
ZCDTth
0.8V
Vaux
ZCD
T
ST RO BE
1V
BL ANK
A
C
F
D
0
) and the ZCD circuit can be erroneously trigged, leading the system to work at
Section 7.11 on page 26
shows the typical waveforms during the power up and the linked T
1. 5
6.3μs
ZCD
BLANK
BLANK
.
is very close to the arming and triggering thresholds (V
BLANK
STROBE
, can have two different values: the lower one is 2,5 μs (typical
when V
4
Mosfet swit ched on by the starter
F
timing diagram
OSC
0. 5
Doc ID 15585 Rev 4
lim
). The time T
defined as for the over voltage protection (see the
ZCD
is lower than 1 V.
ZCD
BLANK
> 1V, refer to
has the lower value if is detected V
BLANK
2.5μs
value is the lower one. The
Delay
Table 8 on page 8
Quasi Resonant Operation
Operation description
ZCD
during the
BLANK
ZCDAth
and
selection.
and
ZCD
23/40
t
t
t
t
t
t
t
t
ZCD
,

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