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Old 8th July 2012, 03:32 PM   #11
qusp is offline qusp  Australia
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Quote:
Originally Posted by marce View Post
Anyone listened to Li-ion batteries?
some figures on this thread regarding battery noise.
yeah but not lifepo4 or anything recent, the stuff referenced there is all pretty old articles and doesnt cover this comparatively new chemistry.
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Old 8th July 2012, 03:46 PM   #12
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marce, still no measurements on LiFePOs though, which are generally assumed to be the best choice (low z, stable voltage, best "sound")....
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Old 9th July 2012, 01:44 PM   #13
marce is offline marce  United Kingdom
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Qusp, sorry didn't pay that much attention to the thread after the snotty replies.
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Old 9th July 2012, 03:29 PM   #14
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Quote:
Originally Posted by qusp View Post
use a battery, simple. they want low noise, they are about as benign (not dynamic at all, not high current at all) a load as you'll get. stability is important, just not very hard to achieve
A battery has Z inductive component just as a regulated power supply. The impedance is, in fact, much higher than the Jung regulator. (With a good layout, the Jung regulator achieves Zout of a micro-Ohm or so.)

Click the image to open in full size.

Z out is important because comparators can "stutter" (for lack of a better term) if the supply voltage droops during a transition.

Use a separate regulator for the clock circuitry and local ceramic and electrolytic bypass.
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Old 9th July 2012, 03:36 PM   #15
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No LiFePo's though on those graphs.
Their output impedance is reportedly much lower than that of other types of batteries (even at higher frequencies).
I recall jkenny posting a conference paper on the issue but the link was dead last time I checked. :S

Fingers crossed that qusp has kept a copy or something.
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Old 9th July 2012, 06:49 PM   #16
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No LiFePo's though on those graphs.
Their output impedance is reportedly much lower than that of other types of batteries (even at higher frequencies).
Unlikely that you'll see me shell out $160 for a 12V 7Ah LiFePO4 battery.
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Old 9th July 2012, 07:50 PM   #17
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Unlikely that you'll see me shell out $160 for a 12V 7Ah LiFePO4 battery.
Since the thread is about powering an oscillator, I do not see how a 12V 7Ah pack is relevant. A single LiFePO4 cell will power a clock for good long while, for just a handful of dollars. In fact, a LiFePO4 supply for clocks, including a management circuit and charger can likely be built for less than the cost pf a good transformer based linear supply with a good discrete regulator.
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Old 9th July 2012, 07:57 PM   #18
qusp is offline qusp  Australia
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i'm aware of all the decades old comparisons jackinnj, what sort of a comparison is that? 7Ah vs Jung reg? most Jung regs are severely current limited vs LiFePO4, a single $12 cell is 3v3 @2500mAh … we are talking about clocks here right? thats over 30hrs minimum right there and you can then charge it in less than 1hr show me what sort of super reg you can build for $12, show me its current rating …

sorry TheShaman, I dont have that, I know the paper you are talking about though. by comparison batteries present more advantage than just noise and output impedance. for clocks, floating outputs not being the least handy. capable of FAAAAAR higher current bursts.

the difference between a few mOhms and a few µOhms in practical terms since you have to connect them somehow is pretty meaningless IMO. Its a similar argument as OTT high damping factor when you still need to connect with speaker cables/connectors and often through a crossover. AFAIK super regs need to see some impedance or they ring/resonate, batteries will not oscillate, they are unconditionally stable.

i'm not going to try and say Jung regs are bad, I think its an excellent design and have used them quite a lot over the years, it was the first regulator I ever built. but I wouldnt say they are the better choice here
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Old 9th July 2012, 07:59 PM   #19
qusp is offline qusp  Australia
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ahh I see barrows posted the same response to jackinnj's somewhat erm .....strange choice of comparison.
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Old 9th July 2012, 08:27 PM   #20
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Default qusp...

You just about have me convinced to try a couple of cells for the oscillators. Do you recommend absolutely no decoupling, right now I just use .1uF MLCC on the output of each Trident to each oscillator module.
I would assume that the length of wiring from the cell to the oscillator may be fairly critical, I might have to get creative with layout to keep it short...
Any tips you could provide would be appreciated.
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