Author Topic: How do you find out that 8mm is min creepage distance in offline isolated SMPS?  (Read 8291 times)

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Offline dmills

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That is why triple insulated wire exists, it is a standard thing in transformer winding.

Also, those mylar tapes used inter winding are tough and as long as you design the windings to ensure sufficient creapage around the edge of the tape, a few layers is just fine and I would have no concerns.

The issue with PCBs is surface contamination and that FR4 fairly readily carbonises leaving conductive tracking, been there, seen it, not much of an issue in a transformer, which has at least two thicknesses of insulation to fail even if you took no precautions what so ever (And as I say, triple insulated wire exists for a reason).

Regards, Dan.
 
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Offline CopperCone

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im reconsidering what I said, proper would be an R-core or ring core, with a ceramic shell, with the wire on top.

I took apart a small transformer, I am not impressed by this so called triple insulation. Maybe something special on medical products? But really...  :--

If its gonna be handled by a person, do you really wanna trust some flexible plastic shit?

Of course, being around humans, they do plenty of dumb ass shit all the time to save like, fractions of a penny.
« Last Edit: April 19, 2018, 12:34:52 am by CopperCone »
 
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Offline T3sl4co1l

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Flexible plastic shit is a long sight better than inflexible plastic shit. Polyimide insulation caught several airliners on fire back in the day.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 
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Offline CopperCone

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i wonder if those materials made someone a 50 dollar or 100 dollar bonus lol

i wanna see a plot of the management bonus money vs airliner destruction costs
 
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Offline dmills

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How many millions of designed to the appropriate standard switchmode transformers are out there?

How often do you hear about a primary/secondary insulation failure in such a transformer?

The things are pretty bloody reliable at least if designed to an appropriate specification.

As to the airliner thing, that is what airworthyness directives are for, we LEARN from the mistakes, which is why an airliner going down today is a much rarer event per mile flown then it was in say 1955. 

Companies behaving really badly WRT safety to save a buck are actually much rarer in my experience then you would think, fraud is just more profitable if you are that way inclined (Enron, Worldcom) then say Union Carbide in India cheaping out on cooling plant or BP in the gulf of Mexico not doing the maintenance.
CEOs may sometimes be sociopaths (Not even sure I buy that common meme) but the folk they put in charge of multi million dollar facilities usually know their trade and understand the risks.

Regards, Dan.
 
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