eem2am
Joined: 22 Jun 2008
Posts: 753
Helped: 13
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 27 Oct 2009 12:13 SMPS isolation__safe secondary voltage if >42V ? |
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Hello,
I am doing SMPS’s running from 230Vrms Mains.
Please could you tell which of the following scenarios is safe?
-also please indicate those that violate UK laws.
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Scenario 1:
If I make an offline, non-isolated buck converter with +20V output voltage , -and supposing I touch this +20V output voltage terminal, -then this is too low a voltage to harm me ,…..
….so why do we need “safety isolation” with a transformer in this case?
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Scenario 2:
If I make a non-isolated buck converter with an +80V DC output and I touch the +80V terminal, -then I will be harmed, since +80V is high enough to harm.
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Scenario 3:
If I make an offline flyback converter with an 80V DC output (fully transformer isolated), and I touch the +80V output terminal AS WELL as touching the secondary return terminal , then I will be harmed
(-provided I am not already dead from Scenario 2 ?!)
-The transformer surely provides NO real safety barrier though ?…..since energy can simply pass through the transformer, from the mains.
And the question here, if you would be so kind, is …………….
Which is worse, is it Scenario 2 or Scenario 3?
Am I still alive at this point?
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Scenario 4:
Now (providing I am still alive!) I make an offline flyback converter with an +80V DC output (fully transformer isolated).
I then use a non-isolated buck converter to provide a +20V output from the isolated +80V output.
The +20V output feeds LEDs which are mounted to a heatsink (via insulating pads). This heatsink is open to the world and customers could touch it if they wanted.
Would this product of Scenario 4 be illegal ?
-and is it a killer?
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