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Old 27th February 2007, 07:37 PM   #1
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Default Regenerating the 250V Mains

I am using the UcD400, fed by a 50Hz signal source, to effectively regenerate the 250V mains (utility supply) by feeding it into a transformer.

So far so good, its a technique I've adopted before on a very small scale so I have reason to believe it will be worthwhile (theres lots of garbage on the supply).

However (yes I know theres always a catch) this means that for example my output voltage is 315 volts off load and 250 volts with a 100watt load. What I really need is a means to automatically regulate the ouput voltage so it stays almost constant independant of load.

My Question. Is there a cunning way to do this? Should I go and use something like an LM13700 voltage controlled amplifier or am I making a simple job difficult?

Andy
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Old 28th February 2007, 07:45 AM   #2
Elvee is offline Elvee  Belgium
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Hi

You've basically two options: the high performance, difficult one and the easy, but lame one.
In the high performance scenario, you apply a global feedback from the output of the transformer to the input of the amplifier; you then get a fast, real-time regulation that will not only correct the amplitude, but also the shape of the output wave. The difficulty is similar to that encountered by tube amplifier designers: applying as much of feedback as possible with a transformer in the loop without getting instabilities; and in your case the matters are made worse by the output filter of the amplifier.
The lame option is basically the one you outlined: use a much slower feedback loop to servo the average output of the amplifier. It will work pretty well with steady loads, but the transient response will be very poor.
There is also a cunnig way of implementing the first solution: if you give the amplifier output a negative impedance exactly equal to the impedance of the transformer with its secondary shorted, this will give a zero output impedance, equivalent to a perfect regulation. It may be easier to implement than explicit feedback.
LV
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Old 28th February 2007, 08:39 AM   #3
Eva is offline Eva  Spain
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Simple solution: Get a higher VA higher quality toroid transformer exhibiting better regulation.
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Old 28th February 2007, 10:06 AM   #4
Pano is offline Pano  United States
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Crikey! I think I would have just bought an isolation transformer and maybe some line filters.

You're a brave man, Andy.
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Old 28th February 2007, 10:12 AM   #5
Pierre is offline Pierre  France
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Is it wightstanding well the continuous output power?
I mean, if you load with, say, 300W, can you leave it indefinitely or only during short bursts? The UcD400 is thermally designed for audio, not for continuous RMS output, that's why I ask.
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Old 28th February 2007, 12:06 PM   #6
IVX is offline IVX  Russian Federation
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Andy, i guess couple UcD400 will be better, due to lower stepup ratio is required.
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Old 28th February 2007, 01:34 PM   #7
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Thanks guys.

Well I must say how surprised I am at the UcD400, it barely gets warm with its small heatsink even when driving a sine wave at 100 watts. I would have guessed more than the stated 92% efficiency.

Thanks for the comments about getting a wider loop. I had considered that but like you I worried about stability - my maths relating to feedback loops is not great but from memory I should have a better chance of stability with less open loop gain relative to closed loop gain.

I dont think that getting a bigger toroid would assist. The problem is significantly greater than just the regulation rating of the transformer (less than 5% in my case) as these rating are derived from a situation where the supply has effectively unlimited power whereas my supply has limited power (somewhat more than 100 watts.).

Yes I know the solution may sound like overkill but Lynn Olsons recent posting where his amplifier soundchanged completely when he changed either the utility voltage or its frequency made me think. (He rated it as more important than swapping between the best tomearm in the world to an also ran) I also know what incredible effect a UPS has before my preamplifier - which I find amazing as it uses choke input filters, lots of LC filtering etc so theoritically should be completely isolated from whatever comes in via the utility supply. BUT it is not.

Thanks Guys
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Old 1st March 2007, 11:26 AM   #8
IVX is offline IVX  Russian Federation
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For the USA/Japan standards, would be enough couple UcD700 directly loaded, so it's no bad diy alternative vs stupid 40kg AC Regenerators for $3000 but for 240VAC required other silution indead.
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