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Old 25th May 2009, 07:42 PM   #1
nonoise is offline nonoise  South Africa
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Default Ccs

A Interesting new programmable constant current source
LT3092
http://www.linear.com/pc/productDeta...ign=LT_Insider
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Old 26th May 2009, 02:53 AM   #2
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Why do they call it two terminal? I count three pins.

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Old 26th May 2009, 06:08 AM   #3
lineup is offline lineup  Sweden
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Hi!
It is alright, if it is affordable = budget price

And the crucial question from me is of course:
How good quality
and how clean
is this Costant current source?


And from this follows a second question:
What does this offer, that we can not achieve with 1 ordinary N-JFET ??
Or one JFET + one MOSFET tansistor to provide even much more current than 200mA ??


So, what do I gain, in the end, from buying that one, instead of do it myself.


wonders
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Old 26th May 2009, 02:26 PM   #4
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Realy the specks. arn't all that good using 2 bypass caps it
has a 90db ripple rejection where as a lm317 will give you
about 115db used as a ccs. By the way just out of curiosity
anyone know the ripple rejection of the Aleph ccs?
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Old 27th May 2009, 04:19 PM   #5
nonoise is offline nonoise  South Africa
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Regarding the output noise
Linear claims the following for
Reference Current RMS Output Noise = 1nA RMS
The also have the following appnote on noise reduction

When a reduction in the noise of the current source is
desired, a small capacitor can be placed across RSET (CSET
in Figure 7). Normally, the 10μA reference current source
generates noise current levels of 2.7pA/√Hz (0.7nARMS
over the 10Hz to 100kHz bandwidth). The SET pin resistor
generates a spot noise equal to in = √4kT/R (k = Boltzmann’s
constant, 1.38 • 10–23J/°K, and T is absolute temperature)
which is RMS-summed with the noise generated by the
10μA reference current source. Placing a CSET capacitor
across RSET (as shown in Figure 7) bypasses this noise
current. Note that this noise reduction capacitor increases
start-up time as a factor of the time constant formed by
RSET • CSET

The idea of using a LM317 is very sound indeed, one could also use a small voltage reference chip but connected in a similar way we used it as a CCS for ICP sensors.
Later with the emergence of ICP microphones this trick still worked rather well having enough bandwidth and low enough noise.
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