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Old 8th September 2015, 11:18 AM   #1
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Question Floating PSU

I'm sorry my ignorance, could I do a floating psu without batteries?
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Old 8th September 2015, 12:51 PM   #2
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Floating compared to what?
A simple transformer will detach it (make it float) unless you connect it to earth again.
If I'm right.
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Old 8th September 2015, 03:29 PM   #3
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So if I make a +- psu with 2 tx and 2 diode bridges and two caps and no connect 0V of positive rail and 0V of negative rail to nothing only together two 0V of the 2 psu is the psu floating right?
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Old 8th September 2015, 04:09 PM   #4
AndrewT is offline AndrewT  Scotland
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A transformer gives you an isolated supply.
If you rectify and smooth that supply it is still isolated. The voltage limit on isolation is provided by the primary to secondary insulation. Mains transformers are usually short term guaranteed to >1kV, but i would not rely on any more than the maximum peak of the mains voltage rated for your transformer. For an EU 230Vac rated transformer that would be ~350Vpk.

It is how you connect that isolated supply that determines whether it remains isolated.
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Old 8th September 2015, 04:17 PM   #5
rayma is offline rayma  United States
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Quote:
Originally Posted by merlin el mago View Post
I'm sorry my ignorance, could I do a floating psu without batteries?
Yes, this has been done for many years, for example in the Circlotron amplifier circuit.
Just don't connect the supply to ground anywhere, and observe the voltage isolation
requirements, especially in the transformer and filter capacitors. Metal capacitor cans
(with or without insulation) would have to be isolated, for example.
Circlotron History

Last edited by rayma; 8th September 2015 at 04:27 PM.
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