[sdiy] LF357 as follower / departure from ideal opamp behaviour

[James Patchell]

The LF357 is a decompensated version of the LF356...what this means is, the 
minimum stable closed loop gain is about 5...with a close loop gain of 1 
(follower)...it is probably oscillating, and this is what is causing the 
apparent DC offset...

The LF356 is the same part...but compensated for a gain of 1....

Unless of course...you are actually talking about the LF347 which is a quad 
opamp (I bring this up, since you seem to be comparing the LF357 to the 
TL074)....



At 05:16 PM 2/15/2006 +0100, Karl Ekdahl wrote:
>Hellu, i'm doing a s&h around a LF357 since it's
>supposedly pretty good for this. But, a 2v input
>follower gives about 2.5v out which isn't nice at all.
>I'm guessing this has to do with some non-ideal
>behaviour of the op.amp. but i'd like to know which
>parameter that's screwing it all up! Also, i'm using
>the LF357 because of its low input bias (30pA typ). I
>later noticed that a regular tl074 has the same max.
>input bias as the LF357, but double the typical, how
>much better could i "generally" expect a LF357 to
>be???
>
>thanks
>
>Karl

         -Jim
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