Electronics > Beginners
What does it mean "to leak VAC" for a PSU?
(1/1)
analogo:
In the thread "TS100 doesn't function properly when earthed" users Rooster Cogburn and Gyro discuss the implication of a non-earthed PSU connected with a 3-prong cable. They use expressions like


--- Quote ---This brick PSU is certainly not mains earth referenced and leaks plenty of AC like most SMPS units

--- End quote ---

or


--- Quote ---I must have like a hundred devices here with cheap SMPS that each have ~50% mains VAC between their ground and mains earth.

--- End quote ---

or


--- Quote ---the output floats to half mains voltage due to the EMC filter caps.

--- End quote ---

Could someone explain what is this AC leakage and how it can be detected?

If I had an oscilloscope (I don't), could I measure the voltage between mains earth and the -V of the 12V PSU output and see an oscillating wave with amplitude 120V (240V/2)?

What about probing earth and +V? Would I get an oscillating 108V wave (240V - 12V)?

If so, isn't that extremely dangerous? How could it be that Rooster has hundreds of such PSUs in his house?
madires:
The last quote is the answer ;) SMPSUs usually have an EMI suppression cap between primary and secondary side (typically 2.2nF class Y2). That cap passes a mains referenced low current from the primary side to the secondary side. It's not dangerous but can give you a tingle. To check for the cap simply take a DMM and measure the AC voltage between output (ground in most cases) and mains earth.
Navigation
Message Index
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod