Which Of the components fails most often in low power offline SMPS?

[treez]

Hello,
Which of the components in a low power (<20W) offline SMPS (flyback) would be likely to be most vulnerable to failure?...

1..Switching FET
2..Mains rectifier diodes
3...MOV at mains input
4..Electrolytic capacitors in primary
5...Electrolytic capacitors in secondary
5...Primary side PCB fuse blows (eg due to mains surge etc)
6...Output diode
7...X caps
8...Y caps

 

[betwixt]

5 then 4 in my experience.

Brian.

 

[treez]

OK, thanks, i should have said that I am talking about a "failure" that totally stops the light from working...as opposed to say, a 25% drop in capacitance which may be called a "failure" in certain industrial circles.

 

[Kripton2035]

5 then 4 then 1
2 if there has been a surge on the ac input

if a capacitor of the secondary has a drop in capacity, or a high in esr, then the smps stops functionning
and sometimes this high esr destroys the main switching mosfet.

 

[treez]

Thanks, of course, as you know, all of these "demons" exist in mains LED lightbulbs, so I am not sure why they always quote the LED lifetime of 50000 hours when quoting bulb life?

 

[Kripton2035]

make yourself a regular non smps power supply
led dont need much current, so your power supply will really last more than an smps one,
or replace the capacitors in smps with known good brand names low esr caps ( Panasonic, Rubycon, Chemicon, Nichicon )

 

[betwixt]

Or, better still, increase the switching frequency by several magnitudes and use dry capacitors. Oh, and develop faster diodes to do the rectifying. I'm busy right now but I'll have it all worked out by tomorrow :-D

Brian.

 

[andre_luis]

Hello,
Which of the components in a low power (<20W) offline SMPS (flyback) would be likely to be most vulnerable to failure?...

1..Switching FET
2..Mains rectifier diodes
3...MOV at mains input
4..Electrolytic capacitors in primary
5...Electrolytic capacitors in secondary
5...Primary side PCB fuse blows (eg due to mains surge etc)
6...Output diode
7...X caps
8...Y caps

This can be fully answered on PDF document referred on topic bellow, which brings parametric way to predict its lifetime :

https://www.edaboard.com/threads/205648/#post867215





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