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|20th February 2007, 05:19 PM||#1|
Join Date: Jan 2005
Newbie voltage regulator question
Ok Im pretty new to diy electronics. I have built a bunch of kits
Chipamp.com 3886 gainclone
41hz Amp6 Tripath amp
Scott Nixon Dac kit
a few diy speakers
So I have expereince building kits and have had good results. And I have a basic knowledge of electronics, i know the differance between capacitors, resistors...etc and what they do and i can read a basic schematic. But I never really understood how or why these kits I built worked. But recently I have been getting much more interested in this aspect of the hobby. I have been reading alot and Im taking an electronics course at my college. I have started to build very basic circuits to get an idea of how they work. I just built a very basic Cmoy headhone amplifier to learn about opamps and power supplies. I tried a few differant battery power supplies first since they are safer and easier and now im ready to try some basic linear supplies. Im doing a regulated supply right now and it got me wondering. Is there any benefit to use more then one regulator. For example if you have a 15v transformer and you wanted to get a regulated 5v output. Is there any benefit to using a 12v reg followed by a 5v reg? Does this result in a cleaner 5v output then the 5v regulator alone would? Sorry if this is a dumb newbie question im just trying to learn. And id like to thank all the great and helpful people on this forum I have learn lots in the past few months!
|20th February 2007, 05:49 PM||#2|
Join Date: May 2002
Location: The great city of Turnhout, BE
Blog Entries: 7
Re: Newbie voltage regulator question
In theory, and measurably, the final 5V would most probably be cleaner. BUT it also depends on the layout. If you have been reading on power supplies you probably have been reading about 'start ground". It is very important to have a good layout, otherwise the results of 2 supplies with bad layout will be worse than 1 supply with good layout.
If you are starting in this area, I would recommend to start with a single supply. There is enough in it to stumble over even without the complexity of TWO of them in series.
|25th February 2007, 04:37 PM||#4|
Two regulators in series does matter if the unregulated supply is very noisy. If you don't care about the cost or if you really need it you can get on the safe side with to regulators, no harm. If you just want to the right or optimum thing, there is more to it.
The regulator themselves can be various noisy as well and differs in response to loading over the the audible frequency range (or the range the circuits can work with). Then a op-amp or a well constructed discrete amplifier supresses the power supply some bit also. A good design goal is to have a margin of 20db (or ten times) in respect to almost anything, which for example could be:
- nominal signal level 1Vpp
- s/n ratio 100 db
- design margin 20 db
--> total s/n ratio 120 db
--> max noise 1uVpp on the output (very hard to achive irl)
- amplifier supply suppression 40 db
--> power supply noise&ripple can be around 100uVpp
- regulator ripple rejection 40 db
--> unregulated power supply noise&ripple must be 10 mVpp, hard but not unrealistic to achive.
Maybe this is a bit "easy" way to do the math, but it works.
In my next project I willl use an external transformer, then a RF/LP-filter, a rectifier, one or more C-R-C-filter ("passive pre-regulation"), followed by a LT1763, which I believe have excellent caracteristics for audio, 20uVrms (28uVpp) noise for 10Hz-100kHz, fast response and at least 50db ripple rejection. You can find Linear at www.linear.com.
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