May be this is a weird question. But I am little curios to know why my 12V DC adapter is giving shock when the circuit is complete.
I purchased couple of these 1 AMP 200V AC to 12V DC adapter. Unfortunately they didn't come up with a 'data sheet' as such except the specs written on the enclosure of the adpater. It is for sure not a transformer-less adapter. I verified that. When I connect it with as input to my DC to DC converter, the converter parts give electron shock. Well, I must say it never seemed as strong as 220V AC shock. A mild shock, but everytime.
What might be the reason for this? To my knowledge if it's pure 12V DC, I am not supposed to get shock. Is it possible that the DC is not well filtered and some AC components are still left in the adapter's output which is causing the shock. The other day I say a Youtube video where the presenter demonstrated that 12V AC exceeds the comfort level of human being, and one would feel the shock. Is this the case happening here?
If yes, then my last question would be how can I get rid of that? Would a capacitor filter work?
Answer
The most probable reason for the electrical shock is the value of the (Y-rated) capacitor that sits between the mains side of the adapter and the low voltage output.
This capacitor is needed to provide a return path for the high-frequency (about 100 - 200 kHz, not that high) with which the isolation transformer is fed.
If the value of this capacitor is higher than what is usual (1 nF) then you might feel a "tingle" when touching the output of the adapter.
Also see this question and perhaps this question as well because it shows a picture of a mains adapter PCB where you can clearly see the blue capacitor C5 across the yellow transformer.
As long as the shock is just a "tingle" then it should not harm. But properly designed adapters should not give this "tingle" !
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