VIPER12A-E STMicroelectronics, VIPER12A-E Datasheet - Page 9

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VIPER12A-E

Manufacturer Part Number
VIPER12A-E
Description
Fixed frequency off line converter
Manufacturer
STMicroelectronics
Datasheet

Specifications of VIPER12A-E

Constant Current Output
350 mA, 700 mA, 1.05 A (selectable)
Input Voltage Range
90 to 264 VAC 50/60 Hz

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Feedback pin principle of operation
A feedback pin controls the operation of the device. Unlike conventional PWM control
circuits which use a voltage input (the inverted input of an operational amplifier), the FB pin
is sensitive to current.
Figure 5.
The power MOSFET delivers a sense current I
R2 receives this current and the current coming from the FB pin. The voltage across R2 is
then compared to a fixed reference voltage of about 0.23 V. The MOSFET is switched off
when the following equation is reached:
By extracting I
Using the current sense ratio of the MOSFET G
Internal current control structure
S
:
Figure 5.
I
Doc ID 11977 Rev 2
D
presents the internal current mode structure.
=
R
G
2
ID
(
I
I
S
S
I
S
+
=
I
=
FB
0.23V
--------------- - I
R
G
)
2
ID
s
=
ID
which is proportional to the main current Id.
0.23V
:
0.23V
--------------- - I
FB
R
Feedback pin principle of operation
2
FB
9/21

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