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Question
hello,
please tell me, if i am using a grounded voltage multiplier as a source of HV DC to create air ions, would the transformer from the wall socket be best as regulated or unregulated. the amperage that will be flowing through the HV circuit is only <70 micro-amps (so almost negligible), but i need it to develop the full voltage (25kV) at the HV terminal. i read how the regulation of the transformer is crucial when the circuit is not under load in order to develop the full voltage as one or the other will not develop the full voltage unless the circuit is under load, but i can not remember which it is; regulated or unregulated. i think it was that the unregulated only supplied the current if there was a circuit but a regulated transformer develops the full voltage without there needing to be a load, is this correct?
thank you,
gene

Answer
Hello gene,

I have revised the last paragraph.

Check out what wikipedia has to say about transformers.
http://en.wikipedia.org/wiki/Transformer
They don't use the terms regulated or unregulated. With transformers, the terms regulated and unregulated reflect the amount of care taken to minimize the causes of output fluctuation. The term regulation might suggest actively monitoring the output and making adjustments in some way to control the output to the desired voltage. I don't think that is what is meant in what you have studied. I believe that if you see the terms regulated or unregulated applied to transformers, it is a matter of the output voltage of the regulated transformer having been designed with more care to limit significant fluctuation when load changes from none to maximum.

In some applications, poor regulation is an advantage. The transformer used for florescent lights is one example.

The output of a transformer will normally be greater when under zero load. When a load is drawing current, there will typically be a decrease in the transformer's output voltage. But using a larger gauge wire in the windings will minimize that.

The characteristics (power factor) of the load can reverse the tendency for the output voltage to drop when output current increases, meaning output voltage could increase under load. I don't know enough about your voltage multiplier to know if that would happen in your case.

A perfectly regulated transformer would produce nominal output voltage whether loaded or not. Such a transformer does not exist. The fluctuation can be decreased with careful design, but not 100% eliminated.

You asked: "i think it was that the unregulated only supplied the current if there was a circuit but a regulated transformer develops the full voltage without there needing to be a load, is this correct?"
You asked about the unregulated transformer supplying current and compared it to a regulated transformer supplying the full voltage when both are in a no load situation. Neither will supply any current if there is no load for the current to flow through. But both would supply voltage in a no load condition.

Your current is low, but at that voltage the output power of the multiplier would be 1.75 Watts. Assuming efficiency of your multiplier of 50%, that means the multiplier's input power (transformer's output power) is 2.6 W, or less depending on the multiplier's power factor. Choosing a transformer built for higher power would probably give better regulation.

Other links I have found that may help your studies:
http://electronics.stackexchange.com/questions/7033/why-are-transformers-unregul
http://ecmweb.com/basics/basics-transformer-voltage-regulation
http://www.allaboutcircuits.com/vol_2/chpt_9/6.html
http://www.electrical4u.com/voltage-regulation-of-transformer/

I hope this helps,
Steve

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Steve Johnson

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I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.

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