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We are developing a household device, which consists of a +48VDC power supply and a PCB, where everything is located inside a grounded metal frame. The only parts that come out of the metal frame is a CAN connector and the Power Inlet for 230VAC.

According to IEC 60335 for household devices, the surge voltage is +4kV (level 4) for the power line and +2kV for other I/Os, which means that I need good protection for my PCB.

As a power supply, we are using the UHP-750-48 (https://www.meanwell-web.com/content/files/pdfs/productPdfs/MW/UHP-750/UHP-750-spec.pdf), where already the first problem occurs. This power supply is only tested for surge voltage up to 3kV and the same for EFT. Now there seems not to be really many power supplies in this power class, that have level 4 protection for this except medical power supplies and I'm really questioning what I can do to pass this level of protection.

If the power supply lets some disturbances to the +48VDC line, I need to protect the PCB itself. At the moment, I protect the input with a 8.0SMDJ54A TVS diode and a lot of ceramic and bulk caps, but I'm unsure if there would be a better protection? For EFT this should be fine, but for the high 4kV surge pulses, I think it will blow up, but I have never tested a circuit before on this level.

For the CAN bus, I use the following protection:

enter image description here

Also here, this is mostly for EFT and ESD, but I also doubt here, that it will be enough for 2kV surges. Also on any bus voltage, there are TVS diodes, everywhere are decoupling caps and also on any connector there are TVS diodes.

So my questions in the end are, how can one properly protect a PCB from the surge pulses and second, how can I solve the problem with the power supply?

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  • \$\begingroup\$ This power supply is only tested for surge voltage up to 3kV - then there is no guarantee that this power supply will survive let alone what it might do on the secondary. You need to fix this first. Then concentrate on what happens on it's DC output. \$\endgroup\$
    – Andy aka
    Dec 12, 2021 at 16:14
  • \$\begingroup\$ Ok, what seems to be strange is, that in the data sheet it is stated, that it complies with the EN60335-1 for household appliances. I might be wrong, but as far is I know, this means +4kV surges (level 4)? \$\endgroup\$
    – HansPeterLoft
    Dec 12, 2021 at 16:22
  • \$\begingroup\$ I can't help you figure this out. You have to figure this out. I can help you design a surge protector but I can't figure that out. You also need to establish what the 4 kV surge source impedance needs to be. It'll either be 2 ohms (hard) or 42 ohms (easier) but you can't choose. \$\endgroup\$
    – Andy aka
    Dec 12, 2021 at 16:26
  • \$\begingroup\$ The MeanWell datasheet says it is rated for 4kV ESD and CAN PHY datasheet says it is rated for 4 to 8kV ESD depending on conditions. What is it exactly that you are worried about? \$\endgroup\$
    – Justme
    Dec 12, 2021 at 16:27
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    \$\begingroup\$ ESD and surge protection are miles apart in terms of source impedance @Justme \$\endgroup\$
    – Andy aka
    Dec 12, 2021 at 16:29

1 Answer 1

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Level 4 also means 4kV 2 ohms 2000A transient crest waveform

So you choose the series shunt components to survive the test. LC filters can attenuate and TVS can shunt. and fuses can protect.

Electric Meters for homes only have a built-in breakdown electrodes for 6kV.

So you choose the parts need to comply and design or buy a tester for impulse testing. (or pref. rent,borrow,beg steal,barter;) tbd_k$

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