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Dc/Dc Converter input filter

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drkidd22

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I'm working with a DC/DC converter and on the datasheet there is a recommendation for a filtering with 2 caps and a common mode choke. It mentions to use a 450uH PMT-048 choke. can it be any common mode choke that meets the current rating? I'm using a 4A version of the DC/Dc converter. Specifically the MD24D12-833 from wall industries. Is PMT a type of core?

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AnalogKid

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The choke has to handle the current *and* function at the frequencies involved. So a common mode choke designed for AC powerline applications usually does not perform as well as one that doesn't have to handle the low AC frequencies plus as the high frequency switching noise. Unless there is an explicit reason not to use the app note component (won't fit, hard to get, etc.), use the app note component. You don't know if it took Wall 6 months to settle on that part as the best for the job, or it it was the first thing they tried and was good enough to stop looking further. Either way, it usually is risky to move away from manufacturer-recommended parts.

ak
 

ronsimpson

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can not find data.

Here is a graph of a filter I have used. (common mode filter) In this case 1 to 100mhz the filter looks like 1k to 2k resistor in the line. High frequency noise will be reduced. At DC it looks like a 0.4 ohm resistor.
This filter also helps a small amount in diff mode. In red you can see that below 2.5mhz the impedance is below 1 ohm and noise can get through. It shows a resonance at 400mhz.
upload_2017-10-31_14-11-17.png
If you can find graphs like this, you can see what the filter is doing in common mode and diff mode at any frequency.

You should also have graphs like this for the capacitors you are using.
 
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