[time-nuts] Low noise power supplies for time nuts circuitry - 40μV Adjustable Voltage Regulator Board

gary lists at lazygranch.com
Thu Nov 24 20:07:57 EST 2011

The LTC datasheet "crows" about low current in dropout. Yeah, it's worth 
crowing about since not all chip use what is called a "sat catcher" 
circuit. High current in dropout with PNP pass devices can be a problem. 
I've seen Micrel regulators that are horrible in dropout. The sat 
catcher is yet another feedback loop, so it is best to stay out of low 
dropout if possible.

Generally when I buy a LDO, I use the type with a P-fet rather than PNP. 
I'm not sure if any of these exist with low noise. [I'm usually more 
concerned with stability.] TI makes good ones. The P-fet pass device 
doesn't need a sat catcher, so there is one less loop to worry about. 
Having designed both types, I find the P-fet pass much easier to 
stabilize. Bipolar devices don't isolated as well as MOS.

I'm not familiar with rubycon caps. The low ESR large value caps are 
"organic semiconductor." OSCON is a common brand from Sanyo. Finding the 
ultimate cap is nearly as much fun as finding the ultimate LDO. Check 
out Nichicon. Or you can stick with the Rubycon. Glancing at their 
website, they seem to copy the Nichicon product line.

On 11/24/2011 1:37 PM, Tim wrote:
> Hi All
> ,
> I find it interesting that this subject came up just as I was looking
> into cleaning up some of my supplies that power my RB's.
> Anyway....
> I just bought two of these to play with
> http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=130605436528
> and they're based on this device...
> http://www.linear.com/product/LT1764
> regards
> Tim

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