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| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
I'm not an EMI guru but I recently went through a few EMI tests. The first question I would ask is: How good is your power supply model? Is it very representative of what you see in practice? You will probably have to go through conducted common mode, conducted differential mode tests and radiation. We will neglect the immunity part.
At best your simulation model will give you an idea for differential mode only (my opinion). For the common mode part, no component model (spice based) includes the parasitic capacitance between the component and chassis, transformer windings capacitance etc do you follow? You would probably have to come up with a common mode simulation model based on approximations.
Although, the best tip I can give you is look for possible EMI sources:
1) Ringing due to reverse recovery of diodes 2) Ringing due to power switches (mosfets IGBTs etc)
I know fundamental switching frequency is a source but what can we do about it?hahahah Parts you might want to consider:
Add EMI common and differential mode filters to your input and output usually it's a PI filter. If you are using RC snubbers, try using non inductive resistors (regular wirewound resistors usually ring about 5MHz-10MHz range). Be sure to be using a good chasis connection
I hope these tips help you and let me know how your simulation model goes.....It would be pretty cool if your method works.
I'm trying to design a switch mode power supply of about 1200W. And I'd like to simulate the noise I should expect to get from this circuit. So I want to use OrCad Probe to plot out the spectrum in dBuV and compare it with the requirements of FCC.
I know how to do the FFT. But I'm not sure what signal to FFT. Do I need to simulate a LISN that is done in actual FCC compliance testing? Or do I simply do an FFT on the line voltage assuming a small resistance in the line?
Also, I'd like to plot on the same graph the maximum acceptable FCC noise in dBuV, one for commercial, one for residential, for comparison purposes. How do I do that on a plot of dBxx verses frequency?
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