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Is Placid 3.3V stable?
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glt  
#1 Posted : Monday, November 30, 2009 10:45:41 AM(UTC)
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I suppose if I use a single LED in the Vref section, I can set Placid for 3.3V operation. Is Placid happy in this output voltage range?
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Brian Donegan  
#2 Posted : Monday, November 30, 2009 10:54:34 AM(UTC)
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Yes. Replace one of the LEDs with a diode (1N914 or the like) and you are good to go.
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glt  
#3 Posted : Monday, November 30, 2009 12:28:27 PM(UTC)
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Thanks Brian. How about replacing it with a jumper? (diode has negative temp co, the same as LED, thus eliminating 1/2 of the voltage drift)
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Russ White  
#4 Posted : Tuesday, December 1, 2009 4:54:49 PM(UTC)
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The would work but you might need to use a different opamp than the opa227 in that case. You would want an RRIO opamp.
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glt  
#5 Posted : Tuesday, December 1, 2009 10:43:50 PM(UTC)
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OK, I figured this means a rail to rail i/o opamp, and the Vin minimum of the opa227 is at 2V (The single LED has a forward voltage of 2.1V), so with on diode we are too close to the minimum, and thus a diode will add that .6V.

How about using a single green diode with 2.5V forward voltage? Would that be equally low noise?
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Russ White  
#6 Posted : Thursday, December 3, 2009 4:59:45 PM(UTC)
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The reference voltage of 2.7V (Stock LED(2.1V) + Silcon diode(~.6V) in series) would work just fine even with an opa227. I would give that a shot first.

Cheers!
Russ
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