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Is this power supply really isolated in my application ?!!

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hm_fa_da

hm_fa_da

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Hi,

I am going to design a single phase meter ( using shunt as current sensor ) which uses switching power supply like this schematic :
https://media.digikey.com/photos/rdl/dak_14a_schematic.jpg

i know it has transformer, but i doubt about C5 !

my measurement circuit uses a shunt resistor as current sensor, so i have to connect L of 220V AC to ground of my circuit, like :
shuntc.png

so the final schematic will be like :
dak_14a_schematic.jpg

in this condition as you see, there would be AC current on C5 ... ( half cycle )

would this make problem in circuit working ?!
is this a problem ?!!

can i remove C5 at all ? what happens if i Remove it ?

Thanks :)
 

Actually I think there is something wrong about this.
Did You measure with an Ohm meter between Phase and protective earth (without voltage of course)?
You can not remove C5 since this is your return path for common mode noise.
(this capacitor usually only exists in this place with isolated power supplies, maybe there are non-isolated supplies using this but I never seen)
In the second place this protective earth connection can never be connected to your phase.
Protective earth in most cases would be connected to neutral either inside your house or in the transformer house outside,
to put it simple it would create a shortcut.
 

One second thought, in case of full isolation between secondary and primary side there should be some isolation amplifier in the measurement circuit.
The power supply suggests isolation but it all depends on how the measurement signals are processed in this case.
 

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