AN708 データシートの表示（PDF） - Vishay Semiconductors
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AN708 Datasheet PDF : 7 Pages
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AN708
Vishay Siliconix
CONCLUSION
The simple universal-input power supply design that has been
presented combines economy and performance which should
prove more than adequate for the majority of applications. The
overall cost of the supply should rival linear regulators of similar
power level if heatsink cost is considered. Good regulation has
been achieved while maintaining the 3750-V ac
input-to-output isolation mandated by VDE. The Si9120
eliminates the need for any external start-up circuitry. Also,
foldback current-limiting is demonstrated which requires no
feedback across the isolation boundary.
APPENDIX A
The SMP4N60 was tested for ability to withstand repetitive
avalanche currents and for non-repetitive capability.
Inductance values of 12 mH and 94 mH were used. Repetitive
tests were run at 3 A, with 94 mH at 25_C. Failure current was
measured at 25_C and 100_C. Results were as follows:
L = 94 mH
25_C
4.25 A
100_C
2.40 A
L = 12 mH
25_C
7.28 A
100_C
6.40 A
For the 11.1-W flyback supply presented here, the leakage
inductance is specified at 60 mH maximum. The maximum
drain current is set to approximately 1.0 A. Therefore, based
on the above data, adequate margin is present to prevent
avalanche failure.
APPENDIX B
A number of performance parameters of the Si9120 can be
altered by setting Ibias to a value other that 15 mA. At lower Ibias,
higher efficiency can be obtained. At higher Ibias, lower
propagation delays and a wider error amplifier bandwidth are
possible. Also, if a VCC supply other than 10 V is used, Rbias
should be something other than 390 kW. Figure 3 below relates
VCC to Rbias and typical Ibias. The equation given can be used
for points not on the graph.
14.0
13.0
12.0
11.0
10.0
9.0
8.0
5 15 25 35 45 55 65
mA
Ǹ Rbias
+ VCC
–
2.3
V–
Ibias
484
Ibias
75 85
FIGURE 3. Relationship of VCC to Rbias an Typical Ibias
REFERENCES
1) Liu, K.H., “Effects of Leakage Inductance on the Cross
Regulation in a Discontinuous-Mode Flyback Converter,”
Proceedings, 1989 High Frequency Power Conference,
Naples, Florida.
2) Chryssis, G., “High Frequency Switching Power Supplies,”
McGraw Hill 1984.
3) Billings, K., “Switchmode Power Supply Handbook,”
McGraw Hill 1989.
4) McLyman, Col. W.T., “Transformer and Inductor Design
Handbook,” McGraw Hill 1988.
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Document Number: 70581
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