AN701 View Datasheet(PDF) - Vishay Semiconductors
Part Name
Description
Manufacturer
AN701
Vishay Semiconductors
AN701 Datasheet PDF : 19 Pages
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AN701
Vishay Siliconix
+
36–72 V
DC
C1
3.3 mF
100 V
–
SHUTDOWN
C2
3.3 mF
100 V
R1, 1 W
R2, 1 W
R3
220 W
C3
220 pF
SYNC
C4
100 pF
D3, D4 LS4148
IC1
Si9420DY
TX1
PL-25
D5SC4M
L1
EF12.6
9.7 mH
35 T
11 T
D1
11 T
D5SC4M
D2
C10
10 mF
25 V
+
5V
4A
C11
10 mF
25 V
–
C8
22 pF
C5
D3
R4
10 W
2.2 mF
25 V
14
13
12
11
10
9
8
R5
68 kW
Si9114A
VCC
SENSE
OUT
–VIN
SYNC
COSC
ROSC
+VIN 1
2
SHD
3
VREF
NI 4
FB 5
COMP 6
SS 7
C7
100 nF
R7
390 k
6
5
4
1 kW
TCMT1020
IC2
1
2 47 W
NC 3
C12
2.2 nF
R11
1 kW
R12
1 kW
1 kW
R6
C6
100 nF
IC4
TL431
R10
1 kW
Figure 22 DC-to-DC Converter Block Diagram
Since this choke must carry the full output current, the
minimum number of turns required on this core is given by:
Lchoke x IChoke
Nmin + Bmax x Amin
The result yields a choke having a dc resistance of 22 mW and
therefore a dc copper loss of P = I2RDC = 9 x 0.022 = 200 mW
with 3 A dc. Using a core set with an AL value of 45, a
transformer of L = Nmin2 x AL = 122 x 45 x 10-9 = 6.48mH was
calculated. Measured value was 9.73 mH: slightly higher, but
acceptable.
where Bmax is the maximum flux density used, and Amin is
the minimum core area. In this case Bmax = 200 mT and
Amin = 13 mm2. Substituting in this equation yields:
8 mH x 3 A
Nmin + 200 mT x 13 mm2 + 9.2 T
In this case it was decided to wind 3 layers of 12 turns of
0.315 mm in one layer each across the bobbin. This allowed
the best fill factor of the bobbin, maximizing copper area.
www.vishay.com
12
TRANSFORMER DESIGN
See appendix A for a design using these specifications.
PERFORMANCE RESULTS
The switching waveforms in Figure 23 show that the resonant
reset is limiting the peak voltage to 120 V, well below the
maximum rating of 200 V. Note the leading edge spike caused
mainly by the peak gate current.
Document Number: 70575
16-Jan-01
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