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Old 21st November 2007, 07:22 PM   #1
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Join Date: Aug 2003
Location: Cheltenham
Default LM329 Voltage Reference

Hi Guys,

I added an LM329 Voltage reference to a basic 317/337 (+15/-15v) regulator circuit in my Arcam CDP. I'm pleased with the results so i'd like to add the LM336 2.5v reference to the +5v supply - but i don't know the formula.

Here's the formula for the LM329 6.9v reference (Stolen from Neil Mcbride's hi-fi pages):


This second regulator stage is slightly different and incorporates a voltage reference, which improves the output stability, line regulation, thermal regulation, drift and noise by a factor of about 7, and in use it's a lot better audibly than the first one:

--------------
| |
| LM317T |
| |
|adj out in|
--------------
| | |
| | |
o---o o o--------o--o
| | | Vin
| o------o------o--o |
| | | | Vout |
| - - | |
| | | | | | |
| - R5 - R3 | |
| | | | |
o---o--|<--o | |
| | | |
+| - |+ |+
10uF=== | | ===1uF ===1uF
| - R4 | |
| | | |
o------o------o--------o--o 0v


where the voltage reference ( --|<-- ) is given by 2 legs of the 6.9 V LM329CZ:

------
/ /
----------- |
| | |
| LM329CZ | |
| | |
| -|<- | |
| | ||
-----------
| | |
Cut this | | |
leg off ---> | | | | | |

I note that Farnell stock 3 versions of this voltage reference, the LM329BZ, LM329CZ and LM329DZ which are 3 grades of temperature stability (and hence vary in price). The LM329CZ seems a reasonable choice between stability and cost.

The output voltage is approximately given by

Vout = (R4 * a) + 8.125

where

a = (8.125 / R3) + (1.25 / R5)



Can anyone help?

Cheers Matt
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Old 23rd November 2007, 02:50 AM   #2
gootee is offline gootee  United States
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Why not go straight to the source?!

(Hint: ) http://www.national.com

Enter LM336 in the search box and strike the Enter key, or click on the appropriate button, to initiate the search.

In the search results, click on one of the LM336-2.5 links. After you're on the LM336 "product page", click on the first occurence of the word "DATASHEET", or, scroll down to the datasheet line. Then, right-click on the word "Download" and then select "Save Target As", and save the PDF file to your hard drive.

While you're at national.com , you should probably download the datasheets for any other "LM" parts you might use. I also recommend finding and downloading any related Application Notes. If none are listed directly on the "product page", then you can either search the "Knowledge Base", or, pull down the "Design" menu and select "Application Notes".

You will need the free Adobe Acrobat PDF-file viewer, to view the datasheets and appnotes. If you don't already have it, you can go to http://www.adobe.com , and downbload and install it.
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Old 23rd November 2007, 03:08 AM   #3
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Join Date: Jul 2003
Location: Dona paula, Goa
Default Li cell as reference...

I have found that a Li cell(i have not tried other types)works better(much quieter) than a reference IC. Not that this is something new but Li coin cell with an opamp works better for a current source. However, the disadvantage is that the cell has nominal voltage and it is not 3.00 volts but is not a problem as it is the same way for a reference. The cell voltage is stable but reference is not.
The second issue is, u will have to replace the cell and a voltage monitoring ckt may be necessary.

Gajanan Phadte
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Old 23rd November 2007, 06:22 AM   #4
Nordic is offline Nordic  South Africa
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Rather than useing adobe for PDFs download Foxit.... it is not such a memory hog, and is alot faster than adobe...
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Old 23rd November 2007, 01:12 PM   #5
gootee is offline gootee  United States
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Quote:
Originally posted by Nordic
Rather than useing adobe for PDFs download Foxit.... it is not such a memory hog, and is alot faster than adobe...
Thanks for that, Nordic!

For anyone else who wants it, I found the Foxit PDF reader available here:

http://www.foxitsoftware.com/downloads/

I haven't tried it, yet (downloading it now). But the feature set sounds very nice. Among other things, it enables the user to annotate any PDF with text and graphics.

Thanks again, Nordic.

- Tom Gootee

http://www.fullnet.com/~tomg/index.html
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Old 23rd November 2007, 11:23 PM   #6
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Join Date: Aug 2003
Location: Cheltenham
Quote:
Originally posted by gootee
Why not go straight to the source?!

(Hint: ) http://www.national.com

Enter LM336 in the search box and strike the Enter key, or click on the appropriate button, to initiate the search.

In the search results, click on one of the LM336-2.5 links. After you're on the LM336 "product page", click on the first occurence of the word "DATASHEET", or, scroll down to the datasheet line. Then, right-click on the word "Download" and then select "Save Target As", and save the PDF file to your hard drive.

While you're at national.com , you should probably download the datasheets for any other "LM" parts you might use. I also recommend finding and downloading any related Application Notes. If none are listed directly on the "product page", then you can either search the "Knowledge Base", or, pull down the "Design" menu and select "Application Notes".

You will need the free Adobe Acrobat PDF-file viewer, to view the datasheets and appnotes. If you don't already have it, you can go to http://www.adobe.com , and downbload and install it.

Thanks Gootee,

I've already got the Data sheet but didn't think to look on the National site for Application notes etc.

will report back if i find anything

Cheers
Matt
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Old 23rd November 2007, 11:27 PM   #7
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Join Date: Aug 2003
Location: Cheltenham
Default Re: Li cell as reference...

Quote:
Originally posted by gmphadte
I have found that a Li cell(i have not tried other types)works better(much quieter) than a reference IC. Not that this is something new but Li coin cell with an opamp works better for a current source. However, the disadvantage is that the cell has nominal voltage and it is not 3.00 volts but is not a problem as it is the same way for a reference. The cell voltage is stable but reference is not.
The second issue is, u will have to replace the cell and a voltage monitoring ckt may be necessary.

Gajanan Phadte
Hi Gajanan,

I'd rather not go down the battery route because it would annoy me having to change them.

Thanks for the reply though.

Matt
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Old 25th November 2007, 02:57 PM   #8
gootee is offline gootee  United States
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There IS a 5-Volt version of the LM336:

http://www.national.com/mpf/LM/LM336-5.0.html
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Old 29th November 2007, 03:46 AM   #9
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The reference Li cell connected to a fet input opamp will last for years.

Gajanan phadte
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