I have several AC adapters that gives tinkling feeling to my hand when I accidentally touches its output.
The following image shows a typical circuit where there is a capacitor bridging the primary HV side and the secondary LV side.
http://www.st.com/stonline/books/pdf/docs/9682.pdf
I think it has something to do with EMI suppression but touching the output gives tinkling feeling to the back of my hand and there is a relatively high voltage when measured by a DVM w.r.t. real ground.
Why is this capacitor needed and what about the safety implication should this capacitor fails? Why go to HIPOT 5000V testing of the transformer and then ruin that by adding this capacitor?
Secondly, in the ST application note(shown below), is the DOT(polarity) of the HV transformer secondary output winding wrongly labeled? I asked because the explanation by the designer on how the circuit functions indicate it is of a flyback design.
The following image shows a typical circuit where there is a capacitor bridging the primary HV side and the secondary LV side.
http://www.st.com/stonline/books/pdf/docs/9682.pdf
I think it has something to do with EMI suppression but touching the output gives tinkling feeling to the back of my hand and there is a relatively high voltage when measured by a DVM w.r.t. real ground.
Why is this capacitor needed and what about the safety implication should this capacitor fails? Why go to HIPOT 5000V testing of the transformer and then ruin that by adding this capacitor?
Secondly, in the ST application note(shown below), is the DOT(polarity) of the HV transformer secondary output winding wrongly labeled? I asked because the explanation by the designer on how the circuit functions indicate it is of a flyback design.
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