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Switched mode power supplies
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Old 3rd January 2004, 12:11 PM   #11
jackinnj is offline jackinnj  United States
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Switched mode power supplies
Quote:
Originally posted by Magura
A. How about getting +30-0- -30V, is that possible in a reasonable way?

B. How about an option to regulate the output voltage, lets say from 12V to 30V ?

Magura
Ans. A -- yes -- with two transformers, or one very good center-tapped transformers, or one transformer with two secondary windings.

Ans. B - by regulating the duty cycle you can regulate the output (but other things come into play.) use an optocoupler to sample the output, compare to an adjustable voltage reference.

you can also throw a linear regulator on the output -- an LM317 with a pass transistor.
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Old 3rd January 2004, 12:51 PM   #12
millwood is offline millwood  United States
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Quote:
Originally posted by Sch3mat1c
All I've heard is that they are noisy as all hell but nobody's yet given me a reason why this noise can't be filtered,
Tim

I used one (12v 3a) to power my active heatsink. the smps sits next to my jlh without any shielding or additional filtering. Zero noise that I can tell - the smps runs north of 150khz if I recall correctly.

it has 5 parts including the smps regulator.
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Old 3rd January 2004, 01:21 PM   #13
jackinnj is offline jackinnj  United States
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Switched mode power supplies
Quote:
Originally posted by millwood


I used one (12v 3a) to power my active heatsink. the smps sits next to my jlh without any shielding or additional filtering. Zero noise that I can tell - the smps runs north of 150khz if I recall correctly.

it has 5 parts including the smps regulator.
The ancient Sorensen switchers which I bought off EBay have less % noise than a 7805 -- a few millivolts .

whether they are good for music remains to be decided --- I know that some ham radio ops are not pleased with the results on CW and SSB using switchers due to the big pulse demands and the comparatively slow response time (which can lead to RFI.) I guess bigger reservoirs are in order here.
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Old 3rd January 2004, 05:44 PM   #14
Tony Salsich is offline Tony Salsich  United States
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Noise on the output of a switcher is always difficult to 'beat down' to a decent level for audio or instrumentation purposes. It usually takes a small lossy choke and some extra capacitors. After that, a linear regulator can do an amazing job of reducing noise. Most people (I was one) are skeptical of the efficacy of the linear as a filter with its limited bandwidth, but it does work with up to 100kHz noise (maybe higher).
It is also important to prevent radiated noise from coupling back onto the output.
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