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caprider 01-19-2022 03:45 PM

Inductor or resistor
 
2 Attachment(s)
See attachment.

This blown component is connected to the output of a bridge rectifier on a SMPS.

It looks like a resistor (it has colored marking lines), but it is marked as L1 on the PCB, suggesting it is a coil. Which is it?

This is a very basic and cheap SMPS which I am analyzing for learning purposes.

Thanks.

PS: don’t worry, I know there are about 330V after that bridge rectifier IF powered and I take the necessary precautions.

eccerr0r 01-19-2022 04:09 PM

Re: Inductor or resistor
 
Still an inductor probably, they do make inductors like that but the ones that look like this are low inductance and low current handling...

caprider 01-19-2022 04:15 PM

Re: Inductor or resistor
 
2 Attachment(s)
So they are both based on “How to diagnose and fix everything electronics” (attached). But what’s their main purpose: coil or resistor?

eccerr0r 01-19-2022 04:18 PM

Re: Inductor or resistor
 
Coil; probably half ^%%#* way of reducing EMI.

caprider 01-19-2022 04:32 PM

Re: Inductor or resistor
 
And how many ohms does it have?
I can’t decide if first and last colors are red/brown (maybe orange?).

eccerr0r 01-19-2022 04:48 PM

Re: Inductor or resistor
 
as low as possible...

redwire 01-19-2022 06:51 PM

Re: Inductor or resistor
 
The part is a ferrite-core inductor used for a differential-mode filter, roughly around 1-5mH. Purpose is to lessen the EMI and RFI noise from the SMPS primary that radiates out to mains. You could read the colour codes for its value.
Cheapest chinese smps and wall-warts don't even have the inductor, they leave it out.
Typically you would see a common-mode choke there but this wall adapter is low power 1.8W output and just a single inductor is used instead.

The part must have got hit/broken somehow.

caprider 01-20-2022 11:56 AM

Re: Inductor or resistor
 
Quote:

Originally Posted by redwire (Post 1100642)
The part is a ferrite-core inductor used for a differential-mode filter, roughly around 1-5mH. Purpose is to lessen the EMI and RFI noise from the SMPS primary that radiates out to mains. You could read the colour codes for its value.
Cheapest chinese smps and wall-warts don't even have the inductor, they leave it out.
Typically you would see a common-mode choke there but this wall adapter is low power 1.8W output and just a single inductor is used instead.

The part must have got hit/broken somehow.

Thanks. I didn’t know coils have the inductance value color-coded.

Based on lines it’s 1mH.

Can I replace it in this power supply with a coil of 1500uH, 100mA, 25Ω?

faraday28 01-20-2022 12:15 PM

Re: Inductor or resistor
 
Basically Coil are inductor because they have inductance value.

Your power supply design is very weird, it usually use with real coil not low powered inductance such as the picture, it blown because it can't hold the heat from current passing through. that's typical cheap power supply, they use wrong parts (cheapest) for easily blown out and you will decide to buy another :))

if you unsure, you can bypass it with jumper wire, because line filter (EMI filter) should be after line input. or you can try the 1.5mH, it doesn't do much.

Most cheapest power supply like this use the design without line filter or X cap or Ycap, because they tends to fail and blow up if they buy from cheapest distributor.

redwire 01-20-2022 09:19 PM

Re: Inductor or resistor
 
Quote:

Originally Posted by caprider (Post 1100862)
Thanks. I didn’t know coils have the inductance value color-coded.
[...] Can I replace it in this power supply with a coil of 1500uH, 100mA, 25Ω?

That DC resistance is too high at 25Ω, and the current-rating 100mA is too low. You need something with lower resistance and higher current rating.


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