AN-4153 Datasheet, PDF (13/16 Pages) Fairchild Semiconductor – Designing Asymmetric PWM Half-Bridge Converters

AN-4153
link voltage applied to the V_DL pin and the leakage
inductance of the main transformer are fixed, the powering
period over the switching period is shorter in high switching
frequencies. As C₁₀₇ is charged, the switching frequency
decreases so that the powering period over the switching
period increases. It is helpful to start SMPS with the internal
soft-start time together.
Design Example
In the design example, 2.2 µF and 12 kΩ are selected as C₁₀₇
and R₁₀₇, respectively.
APPLICATION NOTE
4. Design Summary
Figures 13 and 14 show the full schematic of the reference
design and its transformer configuration. Table 1 shows the
detailed wire information of the transformer. The electrical
features of the transformer are described in Table 2.
Figure 13. Full Schematic with Components Values of the Reference Design
1
2
3
4
NP
5
6
7
8
16
3 mm
3 mm
15
14
13
8
NS
12
27 28 29 30 31 32 33 34 35 36 37 38 39
26 25 24 23 22 21 20 19 18 17 16 15 14
11
1
1 2 3 4 5 6 7 8 9 10 11 12 13
10
9
654321
16
9
Figure 14. Transformer Construction of the Reference Design
© 2008 Fairchild Semiconductor Corporation
Rev. 1.0.0 • 12/9/08
13
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