Electric safety regulations? Pushing the limits of galvanic isolation

Thread Starter

Jaimesg

Joined Sep 10, 2017
7
Hi, I'm designing a relatively isolated resonant power supply (mains to 12V) and the problem is the 12v output and ground which are used to charge a battery, are isolated from rectified mains by a couple of reversed diodes, imagine something like this (of course it won't work because the resonant converter is not present, but just to simplify):

Imagine R4 is the battery, So the question is, would something like this pass electric safety requirements in the US or Europe? Could it get certification? The circuit is safe unless any of the reversed diodes fail, so I don't know how would it be with a regulation like FCC or even CE.


Thanks
 

MaxHeadRoom

Joined Jul 18, 2013
25,982
If you have used the earth ground as you indicate, you will blow the rectifiers.
Where is the galvanic isolation occurring?
If you do have galvanic isolation, then you can earth ground the common of the supply as you indicate.
Max.
 

Thread Starter

Jaimesg

Joined Sep 10, 2017
7
If you have used the earth ground as you indicate, you will blow the rectifiers.
Where is the galvanic isolation occurring?
If you do have galvanic isolation, then you can earth ground the common of the supply as you indicate.
Max.
Hi, Thanks for the answer. Sorry, the circuit won't be earthed, I placed that ground terminal for the scope in the software to work properly (multisim). Please take a look a this other one:



But even if the earth is placed there, the diodes are reversed and I don't think anything would happen. There would be only a very small current flowing due to leakage and parasitic capacitance.

There is no galvanic isolation like the one a transformer could provide. But there is a degree of isolation from the reversed diodes.

Any idea about the regulations?

Regards
 

MaxHeadRoom

Joined Jul 18, 2013
25,982
The circuit would have to be double insulated OR if metallic enclosure, this would be earth grounded.
Then it should be OK.
Trust me, if you ground the DC common as you show in the OP, you will blow the bridge.
Max.
 

tcmtech

Joined Nov 4, 2013
2,867
, So the question is, would something like this pass electric safety requirements in the US or Europe? Could it get certification? The circuit is safe unless any of the reversed diodes fail, so I don't know how would it be with a regulation like FCC or even CE.
No it would not being diodes do not provide galvanic isolation. Only a transformer can do that.

As for battery change what exactly is the point of going through the hassle and costs of getting a poorly thought out and made circuit certified to do a job that there are millions of other better circuits in devices already on the market that cost next to nothing to buy?
 

Thread Starter

Jaimesg

Joined Sep 10, 2017
7
No it would not being diodes do not provide galvanic isolation. Only a transformer can do that.

As for battery change what exactly is the point of going through the hassle and costs of getting a poorly thought out and made circuit certified to do a job that there are millions of other better circuits in devices already on the market that cost next to nothing to buy?
Thanks, I had my doubts too.
Because I'm trying to make it small and efficient.

Regards
 

tcmtech

Joined Nov 4, 2013
2,867
Thanks, I had my doubts too.
Because I'm trying to make it small and efficient.
Capacitive coupled power supplies tend to set the limits on efficiency. 98 - 99% is not unreasonable given the only losses are in the coupling capacitors ESR losses and the rectifier diodes forward drop losses.

Down side it they do not have galvanic isolation and we can't really discuss them here in detail other than mentioning they exist. :(
 
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