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參數(shù)資料
| 型號： | L7833S |
| 廠商： | International Rectifier |
| 英文描述： | HEXFETPower MOSFET |
| 中文描述： | HEXFETPower MOSFET的 |
| 文件頁數(shù)： | 8/12頁 |
| 文件大?。?/td> | 268K |
| 代理商： | L7833S |
8
www.irf.com
Control FET
!"
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# $
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P
loss
= P
conduction
+ P
switching
+ P
drive
+ P
output
This can be expanded and approximated by;
(
)
P
loss
=
I
rms
2
×
R
ds(on)
+
I
×
Q
gd
(
i
g
×
V
in
×
f
+
I
×
Q
gs2
i
g
×
V
in
×
f
+
Q
g
×
V
g
×
f
)
+
Q
oss
2
×
V
in
×
f
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%&
!"
"
)
#
*
%+
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# ,
#
-
.
#
/
#
Synchronous FET
The power loss equation for Q2 is approximated
by;
P
loss
=
P
conduction
+
P
drive
+
P
output
(
+
Q
g
×
V
g
×
f
(
Q
oss
2
*
P
loss
=
I
rms
2
×
R
ds(on)
)
+
×
V
in
×
f
+
Q
rr
×
V
in
×
f
(
)
*dissipated primarily in Q1.
For the synchronous MOSFET Q2, R
is an im-
portant characteristic; however, once again the im-
portance of gate charge must not be overlooked since
it impacts three critical areas. Under light load the
MOSFET must still be turned on and off by the con-
trol IC so the gate drive losses become much more
significant. Secondly, the output charge Q
and re-
verse recovery charge Q
both generate losses that
are transfered to Q1 and increase the dissipation in
that device. Thirdly, gate charge will impact the
MOSFETs’ susceptibility to Cdv/dt turn on.
The drain of Q2 is connected to the switching node
of the converter and therefore sees transitions be-
tween ground and V
. As Q1 turns on and off there is
a rate of change of drain voltage dV/dt which is ca-
pacitively coupled to the gate of Q2 and can induce
a voltage spike on the gate that is sufficient to turn
the MOSFET on, resulting in shoot-through current .
The ratio of Q
/Q
must be minimized to reduce the
potential for Cdv/dt turn on.
Power MOSFET Selection for Non-Isolated DC/DC Converters
Figure A: Q
oss
Characteristic
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