HELP needed with my design of AC/DC converter

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Hi,

We are designing AC/DC converter using MPS020-5 power IC to get 3.3Vdc @ 0.6A output, just as the attachment added shows.

We will be doing FCC certification and comply with UL 60950-1 safety criteria. For that, we have added fuse and MOV as input protection circuit and Pi filter (after rectifier) for EMI/EMC and to remove unwanted noise (complete introduction and classification of filters and applications http://www.apogeeweb.net/article/35.html).

Do I still require to add additional filter circuitry on input side i.e. X2 cap, CMC etc. for noise removal or provided filter circuit will take care of all?

Also, let me know if it is required to change any component value in current design.
Awaiting for your valuable inputs.

Thanks,

Joshua

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Last Edited: Fri. Feb 9, 2018 - 01:55 AM
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C14 is wrong wrong wrong wrong wrong.

 

Did I say it's wrong.

 

Any capacitor bridging the HV and LV sides MUST be of type Y. Which means it carries a Y certification.

 

 

[E2A]

If that capacitor fails short circuit then you have mains on your output. Not good. Hence the need for a Y capacitor.

"This forum helps those that help themselves."

"If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

 

Last Edited: Thu. Feb 8, 2018 - 09:01 AM
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"This forum helps those that help themselves."

"If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

 

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The use of a earth symbol for what is actually the neutral is not really good.

Last Edited: Thu. Feb 8, 2018 - 09:39 AM
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Kartman wrote:
The use of a earth symbol for what is actually the neutral is not really good.

 

Oh, it's worse than that. As they are using a 2-pin input connector there is every chance it'll be connected the other way around and that pin will be connected to Live.

"This forum helps those that help themselves."

"If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

 

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It's worth noting that the normal way top bring a product like this to market is to build a prototype and then do some in-house testing for compliance before you send it out to a test house.

 

I also have to wonder why you are bothering to design yet another 3v3 600mA power supply when you can buy them for so little money.

"This forum helps those that help themselves."

"If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

 

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I’d look at a commercial product that has passed the tests to see what compinents they used, layout etc.

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Please note the MP020-5 datasheet says: not recommended for new designs....use the MP020A-5...they seem to be pretty much the same, at a first glance (didn't study all the details or numerics).

 

Seems like alibaba could cough up a truckload of these supplies for the price you'd pay for the fuse & coil.

 

 

When in the dark remember-the future looks brighter than ever.

This reply has been marked as the solution. 
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1. Do not connect Neutral to the IC GND.

2. Do connect IC GND to negative terminal of C4 and C5.

3. Secondary winding is reversed.

4. Without X2 cap it would likely fail the conducted emissions test.

5. As mentioned, you need a 1.5 - 2.2n / 250VAC Y cap for C14.

 

What is the purpose of R5 ?

 

The output voltage of 3.3V suggests the load is a sort of microcontroller which requires a stable voltage. This converter regulation will not give you a very stable output voltage. It depends on the load. You might consider to invest in a TL431 and an optocoupler for better results.

 

Once you fix the schematic, come back with the PCB design. I think you need help on that one too.

Last Edited: Fri. Feb 9, 2018 - 12:59 AM
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Brian Fairchild wrote:

I also have to wonder why you are bothering to design yet another 3v3 600mA power supply when you can buy them for so little money.

avrcandies wrote:

Seems like alibaba could cough up a truckload of these supplies for the price you'd pay for the fuse & coil.

There may be product form factor / size restrictions, one PCB requirements.

 

It is difficult to find a such product on Alibaba that has the required safety certifications, long term supply guaranties, to fit the form factor etc. As for the price of the fuse and transformer, the poster can also buy them from China as approved components and build the power supply as required.