lt3837 Linear Technology Corporation, lt3837 Datasheet - Page 13

• Manufacturer Part Number: lt3837
• Description: Isolated No-opto Synchronous Flyback Controller
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Primary Winding Feedback
The previous work was developed using a separate wind-
ing for voltage feedback. It is possible to use the primary
winding as the feedback winding as well. This can simplify
the design of the transformer.
When using the primary winding the feedback voltage
will be added to the V
where N
primary winding turns ratio. Use the circuit of Figure 2
to get more accurate output regulation. In this case the
regulation equations becomes:
where V
mately 0.7V).
R
V
FLYBK
1
=
V
R
BE
SP
FB
2
=
is the base emitter drop of the PNP (approxi-
•
is the transformer effective secondary to
V
⎡
⎢
⎢
⎣
OUT
V
OUT
+
I
OUT
+
IN
I
OUT
voltage so:
•
N
(
ESR R
SP
•
N
(
ESR R
SP
+
+
DS ON
(
DS ON
(
)
)
)
)
−
V
BE
⎤ ⎤
⎥
⎥
⎦
Likewise the load compensation equation needs to be
changed to use N
R
CMP
R1
R2
=
K
FB
1
V
FLYBK
LT3837
•
R
ESR R
SENSE
SP
PG
instead of N
+
• –
(
DS ON
Figure 2
PRIMARY
1
MP
(
V
DC
IN
)
)
•
SF
•
R N
•
so:
1
SECONDARY
MS
•
SF
LT3837
C
13
OUT
3837 F10
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