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6

Document Number: 70581

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

L = 12 mH

25

_C

100

_C

25

_C

100

_C

4.25 A

2.40 A

7.28 A

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

propagation delays and a wider error amplifier bandwidth are

should be something other than 390 k

W. Figure 3 below relates

for points not on the graph.

14.0

8.0

515

25

35

45

55

65

75

85

9.0

10.0

11.0

12.0

13.0

mA

R

V

I

bias

I

bias

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.