Electronics > Power/Renewable Energy/EV's

Whats wrong with Power Integrations Buck?

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Faringdon:
Hi,
Why is this attached Buck deemed to be so bad? (100-265VAC input, 24vout 17W out)
The LNK3209 is run within its current and voltage rating.
The inductor is within ratings.
The SiC diode within ratings.
The circuit will have loads of blown air over it all the time.
So why is it deemed a no-go'er?

LTspice and jpeg attached

LNK3209
https://www.power.com/sites/default/files/documents/linkswitch-tn2_family_datasheet.pdf

floobydust:
What does "so bad" or "no-go'er" or "wrong with" mean as far as power electronics, science and technology?
Have you considered transitioning to a different field of expertise, it could make life much easier. I also see you on Power Integrations forums, can they help?

C9 CBP must be 0.1uF at voltage but it also sets current limit. Did you use a cheap tiny part there, something from the bowels of guangdong?
Not sure D1 is shown as slow 1N4005 and Vf to match D2 as far as regulation goes.

Faringdon:
Thanks, the people who make the chips wont tell us any electrical reason, but just tell us not to do it...we are under pressure to do it this way as its cheaper.
The only elec reason we can think of is if the diode was not SiC...but we use SiC.

dmills:
Going off datasheet is ok as long as you respect the ratings, but even then if the silicon vendors FAE tells you not to do something, you are well advised to take that as a hint.

Particularly with highly integrated high voltage power supply parts like the PI stuff, they are often a bit weird and you really want to follow the app notes because they have likely NOT been well characterised except in those limited number of circuits.

What is the opamp and weird LT thing supposed to be doing, the PI part uses the match between the two diodes to regulate in this configuration so I am a little unclear as to what that additional loop is supposed to do, or even how it is closed?

Unless you want to spend ages with a 'badly behaved mains' simulator and loads of blown out sand, I would be taking the hint, but then I like my stuff reliable.

Faringdon:
Thanks, yes the sim is just my attempt to get the on/off type controlled method of the lnk3209 in LTspice, without me havign an actual proper model for it.

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