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EMI / EMC Design practices

Hello All,

I am designing a controller based on 24VDC supply voltage. It is a process indicator based on a Freescale 16 bit controller and communicates with external devices using CAN or RS485.

I want to subject the product to CE testing.

I just want to know that whether the X and Y suppression capacitors will be required for a 24VDC powered controller also!? I have put across the line (X) capacitors as 0.1uF and 0.01uF.

Also whether my circuit ground should be isolated from the chassis ground, because my unit will be subjected to some tests in which the transient voltages are applied between supply lines (230Vac, 50Hz) and Earth (connected to Chassis of my controller).

Kindly let me know your suggestions about standard design practices, for EMI EMC compliance.

Thanks in advance.

Best Regards, Devendra Jogdeo

Reply to
Devendra
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Capacitors for EMI reduction are used to provide intentional paths for parasitic currents which would otherwise cause stronger radoated or conducted EMI. They are never required, per se, except in the sense that, if you use capacitors for this purpose and they are conductively connected across the mains or from mains to protective ground or any accessible conductive components, then those capacitors must have the proper safety rating such as X, Y, X2, etc. In some cases, equipment powered by 'safety' low voltages may still require safety rated capacitors. A DC/AC inverter is a good example. As a good starting point for a couple of years of intensive study of design practices, I recommend Keith Armstrong's 'Compliance Club' EMI tutorial pages, easily found via web search. Paul Mathews

Reply to
Paul Mathews

X and Y caps are not used in 24 V DC PSUs.

You need to get a book. Try "EMC for Product Designers" by Tim Williams.

Reply to
Barry Lennox

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