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SMPS protection functions

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eem2am

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Hello,

These days, almost every single offline Flyback SMPS, PWM controller IC has the following functions built in to the chip……………

(1)…Auto-Restart (turns off if Vout doesn’t reach regulation value within ~ 80ms)

(2)…Overcurrent protection (current sense resaistor in source of FET)

(3)…Overvoltage protection (Senses bias winding voltage and turns off if too high)

(4)…Overload protection. (turns off if Vout goes out of regulation for more than
~80ms….similar to (1) )

Supposing I use an old PWM chip, such as UC3842.

…..the UC3842 has none of the above functions built in.

Will the resultant SMPS be illegal?…(not conforming to regulations)

Is it a regulatory requirement that an offline SMPS has the above four functions?

Do you know which regulation it is?
 

Miguel Gaspar

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The most important are EMI that are not built in.
The other are the line noise.
And of course the power factor correction.

And they are illegal if you use it in equipment or produce it to sell. But for a probe sin lab they are notillegal.
 
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bobmcbride

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In the old days we had to build the necessary protection discretely. You'll notice in Ti's app notes and old data sheets, examples of how to do this.
As Miguel said most regulatory agencies are concerned with whether or not the product is: safe for the user, won't radiate a lot of noise, and has reasonable power factor. The agencies don't really care if your product fails safely.
 
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mtwieg

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Right, regulators don't have time to analyze fancy active fault protection methods you implement. The bottom line for them is when it fails (and something WILL eventually fail), is it dangerous to people or the grid. So whether you put a fuse on the input or implement some slick overload protection circuitry, they don't care so long as they are safe.
 
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