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what this Capacitor do in SMPS

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FMradio

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Hello sir
I want to know the purpose of this capacitor in SMPS, what would happen if I remove this capacitor?? Actually I want to use the output of the Supply with a circuit which have live AC 110V,

SMPS.GIF
 

It's an Y-capacitor for EMI (RF interference) suppression, please refer to verbose discussions at edaboard about the topic. It's not functionally required.
 

You didn't mention the value of the cap,however I think it's for noise suppression ,however circuit will function properly if removed.
 

ch wazir said:
You didn't mention the value of the cap,however I think it's for noise suppression ,however circuit will function properly if removed.
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Sir you have just repeated Sir FvM Words now tell me, if it is useless then y the Manufacture has used it?? is it important to tell the Value of that Capacitor??
 

It limits the common mode dV/dt between primary and secondary.
If your SMPS is open loop, removing is possible but if there is optocoupler current or voltage feedback it should be in place!
 

Mehrshad74 said:
It limits the common mode dV/dt between primary and secondary.
If your SMPS is open loop, removing is possible but if there is optocoupler current or voltage feedback it should be in place!
Click to expand...

sir it do have a Optocoupler, basically its my Scope Power Supply & i want to measure the Live 110V AC, when i connect the Ground pin of my scope to live it maakes lil sparke, i think dude to this capacitor the current path is completing, now what should i do ?? is it OK to means live 110V?? i have measured many times
 

you can use an isolated 110v/110v( about 20w I guess if its digital) transformer to supply your scope.
this also will make your power probing safer....
 

Removing this capacitor caused microcontroller to malfunction in my circuit. In some circuits EMI may not cause interference to control circuit.
 

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