[sdiy] Bipolar Rail to Rail Opamp recommendation

Schwarz Raphael raphschwarz at gmail.com
Mon Mar 2 15:46:11 CET 2020



> Le 2 mars 2020 à 15:45, Schwarz Raphael <raphschwarz at gmail.com> a écrit :
> 
>>> I read it so, that you're actually interested in clamping the input voltage. Why not bias the diodes to +5.8 and -5.8v instead?
>> 
>> It is more like +-4.2 actually. :)
> 
> 
> It’s actually a good idea
> 
> I realized I overlooked the variation with forward current and temperature, 
> 
> I was a taking for granted the 0,8v drop , at 25° and 10mA it’s actually much less
> 
> About 0.24v on a bat54s (what I was using)
> About 0,65v on a 4148. 
> 
> Real life testing of a bunch of diode is consistent with this. My simulator has a very simplified model of diodes
> 
> I wonder if biasing to about 4.75v is a practical solution with part tolerance , out of a bunch of bat54s I randomly tested it seems to only vary by a few mV
> 
> temperature variation is not crazy for 10ma datasheet says 0,3v at 0° and 0.2v at 75°. So about 1% of 5V from 0° to 75°
> 
> So it might be doable
> 
> I still think a good rail to rail opamp would be a more elegant solution
> 
> 1% of 5v is 50mV : something that could fit that range or slightly better would be enough. The application is keeping a bunch of gain to a maximum.
> 
> Best,
> Raphael





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