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Curently I'm working on a design (for my own domestic use only) which is to be supplied by 230 V/50 Hz mains.

The IEC cord will be connected too one of these: Mains Filter with Fuse Internal Connections

After that, the following circuit is used to convert the 230 V into 2x 15 V (2x 3 W): enter image description here

The low-voltage side is rectified and then PTC-fuse protected. PE is not connected to GND. The project uses a plastic housing. There is no switch-mode DC-supply involved - all linear.

As this is my first "real" attempt to design a project with mains-supply, I want to ask some questions to the pro's:

  1. Is there any obvious safety problem? (Wires between connector and PCB all spade-connector with heatshrink protection)
  2. Are there any parts missing, wich should be included into a proper design? (Inrush limiting is not required)
  3. Is the single mains fuse sufficient, or should I include 5x20 mm fuses (not PTC) on the secondary sides?
  4. What are the recommended PCB clearences for 230 V? I would be going with 3 mm between mains-copper and 10 mm between mains and secondary/DC.
  5. Are any parts missing to pass (a hypothetical) certification?
  6. What are common certifications for devices powered from mains and used domestically? CE, TV, VDE - what is commonly tested? (Only regarding the power supply and outside connections)
  7. What should I do with PE? Connect it to GND? Connect it to GND with 47p||1Meg?

Thank you!

EDIT 1:

Here is the secondary-side of the transformer including the DC circuit. Current draw on the 15 V RMS (~20 V DC after D-drops) is rather low with ~100 mA per tap.

First, right after the transformer, there are more MOVs (As good measure, not sure if required. I included them as some sort of "ESD/Overvoltage/For good feeling" protection).

Low-Voltage Side MOVs

Then, the transformer output (15 V RMS nom. @ 230 V RMS in nom.) gets rectified and smoothed (2000 uF in sum per tap). There is a 200 mA PTC to protect the transformer against gross overcurrent (shorts and so on) - and to limit inrush to some degree (Not worried because of 2000 uF only).

Rectification 78xx Rectification 79xx

Afterwards, there are a bunch of 78xx's and 79xx's (On the second transformer winding) LDOs. They all follow the same "building blocks".

LDOs 78xx LDOs 79xx

EDIT 2: As, per @Justme's comment, the MOVs from L/N to PE have been removed. Please see the comments for detailed reasons. Also, please see Article about MOVs for some good information.

EDIT: 3 I added a 10Meg||1N (3kV rated parts, THT) between GND and PE.

ElectronicsStudent
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    At that point it really just comes down to choosing a transformer with safety approvals and double insulation. You might want to skip the MOVs, linear supplies aren't particularly sensitive. If you do include the MOVs, add a thermal fuse. The MOVs will degrade over time and start heating excessively. – Jonathan S. Nov 28 '22 at 02:28
  • @JonathanS. Thank you for the response! The double insulation transformer is required to fullfill Class II standard? And what do you mean with thermal fuse? A PTC in Series with L and N before the MOVs - or a PTC in series with every MOV? May i ask another question: The device is to be used for measurements. I want to have the option, to connect PE to GND directly (e.g Earth referenced measurements) via a relay (So user selectable "earthing" of the front-end). Which precautions do i have to take? – ElectronicsStudent Nov 28 '22 at 05:17
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    If you live in a country where you can plug an earthed plug into a non-earthed socket, I would skip the MOVs to PE. As a hobby project I would skip all the MOVs if you are even a least bit unsure how to make sure they are not a fire or electric shock hazard. To assess the safety, you need to show the PCB for that. To assess requirements for more fuses, you would need to define what you want to protect with the fuse, the transformer, the rectifying circuit, the output wiring, or the powered device. You might want to show the secondary side circuit too if it makes sense. – Justme Nov 28 '22 at 06:13
  • @Justme Thank you for your response! It is Germany - i am not sure about weird edge cases, but all outlets that come into question do have a PE. The cord will be a standard IEC 320-C13 to standard outlet (L, N, PE). I did read up MOV-fire hazards: https://incompliancemag.com/article/new-requirements-for-movs-used-for-surge-suppression-on-ac-mains-ports/ I did not know about that at all - thank you for pointing with your finger! As the mains input is protected with a fuse in the socket, the secondary fuses are intended to protect the transformer. I used PTCs for this purpose. – ElectronicsStudent Nov 28 '22 at 06:43
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    @ElectronicsStudent New buildings may only have Schukos but old buildings may have compatible sockets without PE. And since you can plug the socket in any orientation, there is no guarantee that Live is fused, it might be Neutral. Even more reasons to not have MOVs directly from N to PE, or from L to PE. From L to N the MOV will always have a fuse. – Justme Nov 28 '22 at 06:55
  • @Justme Excellent point! Did not come to my mind. Thank you! I will remove the MOVs from L/N to PE. What is your opinion on the MOVs on the secondary? I did include them, because i saw it in an article/comment online. Are they required? Also: What is your opinion on the PTC protection. The transformer taps are rated for 200mA continuous - as are the PTCs. Current draw will be ~100mA so a fair margin for dT is included. – ElectronicsStudent Nov 28 '22 at 07:06
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    _”What are the recommended PCB clearences for 230 V?”_ It’s not a recommendation, it’s a requirement. For 230 V it is 3 mm air clearance. – winny Nov 28 '22 at 07:36
  • @winny Thank you for your response! Do i read this correct: 3mm copper-copper clearance is required for 230/240 mains on PCBs? – ElectronicsStudent Nov 28 '22 at 16:11
  • For a normal appliance yes. – winny Nov 28 '22 at 18:07

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