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Old 31st July 2015, 10:04 PM   #1
nizse is offline nizse  Sweden
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Default Voltage Regulator Question

Hello.
Im new here and also a real newbe to electronics.
Im trying to settle for a design to build a gainclone and I think that I have decided to use a regulated power supply.
I have found a design for this that I like but when a was looking deeper in to it I kind of realized that I do not understand it...

Click the image to open in full size.

When looking at these positive and negative rails, both LT1083 inputs are rectified the same way and meet at the middle. How does this work?
I cant get my head around it...
And this type of design seems to be widely used.

Looking at an total different design with LM317/337 I can understand it better.
Click the image to open in full size.

Here the inputs to LM317 and LM337 is rectified in oposite ways and the 337 is a negative regulator. This makes more sence to me.

I would like to design the LT1083 the same way, but that would need a negative version I guess.

Anyone who can explain this to a noob like me?
Thank you in advance!
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Old 31st July 2015, 11:22 PM   #2
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If you look at the LT1083 circuit, you will see that it is two separate transformer secondaries creating two separate +30VDC supplies.
Since they are separate and isolated, the 0V (Gnd) output point of the upper supply can be connected to the +30V output point of the lower supply.
If we use that point as our Ground (0V) reference point, the other two output points will be at +30V (upper) and -30V (lower).
Likewise, we could call the -30V point "Ground" which would make the other output points in that circuit +30V and +60V. It is all the same.
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Old 31st July 2015, 11:37 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

The regulator cancels voltage in one case by being
in series with the output, in the other by being in
series with the return to ground.

Say C1 and C4 have 39V and output needed is 35V.
Both regulators will drop 4V with the right polarity.

rgds, sreten.
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Old 1st August 2015, 02:30 AM   #4
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The main thing is what chipamp are you planning on using and also what exactly are your voltage level and current requirements for your power level.

Here is a recent thread and similar discussion that you may want to have a read through in order to help further your education on a suitable regulation circuit.

Lm3886 problem

The LT1083 is a great regulator and I have one in one of my bench supply's but I haven't (needed to) tested it past 2 or 3 amps yet.

FWIW

Jer

Last edited by geraldfryjr; 1st August 2015 at 02:40 AM.
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Old 1st August 2015, 09:45 AM   #5
jitter is offline jitter  Netherlands
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Quote:
Originally Posted by nizse View Post
Hello.
I would like to design the LT1083 the same way, but that would need a negative version I guess.
Other than a lower component count and if a dual secondaries transformer would somehow be unavailable, I don't really see why you would want to change the dual LT1083 (first setup) design to the LM317/LM337 setup (second setup).

It is possible, though, and you would indeed need to change one LT1083 out for a negative regulator.
However, it's noteworthy that negative low dropout regulators seem more prone to oscillations than their positive counterparts (at least the LM337 is). My preference would actually go to the first setup.

Last edited by jitter; 1st August 2015 at 09:49 AM.
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Old 1st August 2015, 10:08 AM   #6
AndrewT is offline AndrewT  Scotland
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Personally, I would use the dual secondary, dual bridge rectifier, dual regulator based on the +ve only 1083, to create two DC supplies.
Then connect these in series. This gives a good dual polarity supply.
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Old 1st August 2015, 10:36 AM   #7
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Quote:
Originally Posted by nizse View Post
Hello.
Im new here and also a real newbe to electronics.
Im trying to settle for a design to build a gainclone and I think that I have decided to use a regulated power supply.
I have found a design for this that I like but when a was looking deeper in to it I kind of realized that I do not understand it...

Click the image to open in full size.

When looking at these positive and negative rails, both LT1083 inputs are rectified the same way and meet at the middle. How does this work?
I cant get my head around it...
And this type of design seems to be widely used.

Looking at an total different design with LM317/337 I can understand it better.
Click the image to open in full size.

Here the inputs to LM317 and LM337 is rectified in oposite ways and the 337 is a negative regulator. This makes more sence to me.

I would like to design the LT1083 the same way, but that would need a negative version I guess.

Anyone who can explain this to a noob like me?
Thank you in advance!
The top one is easiest to understand if you consider it as two batteries in series with the mid point grounded. Each battery is + ... - yet when in series, the lower point is neg to ground...

Jan
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Old 1st August 2015, 10:37 AM   #8
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Quote:
Originally Posted by jitter View Post
Other than a lower component count and if a dual secondaries transformer would somehow be unavailable, I don't really see why you would want to change the dual LT1083 (first setup) design to the LM317/LM337 setup (second setup).

It is possible, though, and you would indeed need to change one LT1083 out for a negative regulator.
However, it's noteworthy that negative low dropout regulators seem more prone to oscillations than their positive counterparts (at least the LM337 is). My preference would actually go to the first setup.
I agree IF you have two separate secondaries, the first setup is measureably better.

Jan
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Old 1st August 2015, 11:41 AM   #9
AndrewT is offline AndrewT  Scotland
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Quote:
the first setup is measureably better
I don't have equipment that can measure a difference.

Some day I will get my FREX LNA built and see if there is a measurable difference.
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Old 1st August 2015, 10:41 PM   #10
nizse is offline nizse  Sweden
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Thank you all!
Thank you for giving me advices and for trying to help.
You make me feel welcome here, and not dismissed.

@ Jan:
You kind of cracked it for me with the two batteries. I feel that I get it now!

@ Jer:
Very interesting thread. Although I havent had time to read more than the first 4 or 5 pages. I will keep reading it all.
What do you think about the LT1083-design above? Will it also suffer from voltagr drop at higher current? Will a pass transistor help out in this design also?

I was also glansing at the 21st century Maida regulator.
But I kind of think it is a bit to complicated for my first amp project...
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