IRAC1166-100W International Rectifier, IRAC1166-100W Datasheet - Page 10

• Manufacturer Part Number: IRAC1166-100W
• Description: BOARD DEMO 100W FOR IR1166
• Manufacturer: International Rectifier

Specifications of IRAC1166-100W

• Main Purpose: AC/DC, Secondary Side
• Outputs And Type: 1, Isolated
• Power - Output: 100W
• Voltage - Output: 16V
• Current - Output: 6.25A
• Voltage - Input: 90 ~ 264VAC
• Regulator Topology: Flyback
• Board Type: Fully Populated
• Utilized Ic / Part: IR1166S, IRF7853
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Frequency - Switching: -

5.4 Mosfet Selection Design Tips
Application note AN1087 has made it easy to understand the calculations required in flyback
sync-rect driving circuits using IR1166 IC. Choosing the right mosfet(s) to satisfy the
performance–cost requirement of any sync rect design should be simple as well.
Voltage rating:
SRs should also follow similar equation in most flyback design as shown below:
Vsd > k*[Vo +(VDCin
startup stress due to leakage spike.
Rds
Generally, it is easy to meet >1% system efficiency improvement if the conduction loss of
the SRs becomes twice smaller than normal passive rectification approach. This is to achieve
better thermal performance especially if the designer wishes to consider not having too bulky
and heavy heatsink in the design, but take note that it would still be largely dependent on
the size PCB copper area allotted to the SRs. We should also consider the estimated Rdson
at 25˚C (normally shown in the datasheet) would be approximately ~1.8 times higher at
Tj=125˚C. As a rule of thumb, we will base our calculation on these assumptions to simplify
the mosfet selection criteria.
For typical 100V Schottky rectifiers, V
should find a 100-V mosfet(s) with lower Rdson which will have a ~150mV max Vsd at rated
full load current (Io
quickly estimate I
Rev.1A
Calculating the rms value of secondary
current is easier for CrCM mode where
D = N*V
N=N
Let V
h = V
P
With h > 2,
Target V
I
eqn.4
Rds
I
2
dis SR
sec
sec
ON
ON
rms
pri
rms
sec
rating:
f
< 1/h* V
(@Tj=125˚C)
/ N
(Schottkydiode)
=
*R
sec
=16.1, Vdcmin=100, D= ~50%
2
SD(@Tj=125˚C)
sec
Io
ds
/ (N*V
ave
ON
,
1 (
WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245 Tel: [phone]
= ~1.8*Rds
−
1 (
f
(@Tj=125˚C)
diode
sec
N = 31/5
D
−
sec
)
ave
D
≤ 300mV
≤ 600mV / 2
18 August 2006
/ V
rms
)
* Io
http://www.irf.com/ Data and specifications subject to change without notice.
+ Vdcin
). For quick estimation of Isec
3 /
sd(mosfet )
since Io
≤ 300 mV* Io
ave
max
ON
/(Npri/Nsec) )]
min
(@Tj=25˚C)
ave
)
is normally given as standard design specs.
eqn.6
eqn.2
f
eqn.3
ave
is around ~ 600 mV ( @Tj=125˚C), so in this case we
eqn. 1
eqn.5
where k =1.1 to 1.4 as a guard band for
Combining equations 4, 5, and 6
Rds
We can use 2-SO8 mosfets (IRF7853)
in parallel having equivalent Rds
(@Tj=25˚C)
Note : Vsd
lower Rdson and can be achieve better
thermal performance but it would mean
raising the parts count and cost.
R
R
DSON
DSON
rms
ON @Tj=25˚C
, designer might find Fig. 9.1 useful to
≤
@
RD#0618
Tj
. 0
of ~9 mΩ.
=
125
25
C
Io
(@Tj=125˚C)
≤
( *
ave
166
50
≤ 10 mΩ
%)
mV
4
Io
=
<100mV would yield
3 [
ave
. 0
1 (
125
−
. 6
D
25
*
)]
0
5 .
=
Page 10 of 24
. 0
010
eqn.7
Ω
ON