[sdiy] 7.5V regulator?

Ian Fritz ijfritz at comcast.net
Thu May 21 05:02:09 CEST 2015

Hey folks!

Thanks for all the great replies.  My present method is to hang zeners off 
the supply rails.  This works pretty well, as the opamp I am using (LMC662) 
has good supply rejection.  But I also use the voltage as a reference, and 
a bit of signal ends up riding on it.  I can improve the stiffness by 
increasing the shunt current, or I can use a separate zener for the 
reference, so I don't really have a big problem.  I do want to keep the 
circuit symmetric, to avoid having to level-shift the signal. And I had 
totally forgotten the trick about lifting the 3-terminal regulators off of 
ground with a resistor!

BTW, the application is a super-duper S/H utilizing the tiny (2 fA) input 
bias of the 662 and tandem switches to eliminate switch leakage.  (H & H, 
ch. 6) I am able to get < 20 fA leakage at 10 nF holding capacitance for 
C0G, PP, and PS caps.  The resistances and times are staggering, plus I can 
easy sample up to 10kHz.


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