Is this circuit stable?

f=20

C,=20

o be=20

In that case, I am probably wrong about the involvement of=20 the regulator.

The offset adjustment won't necessarily be set to the mid position.

Understood.

Lostgallifreyan wrote: (snip)

(snip)

I don't think the DPM needs a very well regulated supply. Have you tried adding an RC low pass filter between the LDO regulator and the DPM supply pin? The current may be high enough that an LC filter would be better. This would help break the feedback loop from the DPM supply current, back through the 24 volt supply to the signal amplifier and back to the DPM input.

A perfect fit if the spec is not a maximum ESR, instead of the actual ESR. I never found capacitors that has specs I could rely on, except for maximum ESR. That is why I always use an external resistor.

John Popelish wrote in news:0Zydnek0FeM-

Yes, I'll try that. I considered it, but there was no space, in the next attempt there will be.

John Popelish wrote in news:0Zydneg0FeNh877bnZ2dnUVZ snipped-for-privacy@comcast.com:

I thought if anything, the ESR might not be as low as claimed, so a series resistor would raise it further. I did take it on trust, but if a maker says 0.5 ohm ESR and it were easily found not to be so when tested by people far more qualified than be, wouldn't there be enough trouble over it for the maker to either meet or change the specs?

If you're saying that this thing might have lower than 0.25 ohm and be on the inside limit for stable use, I can try a 0.5 ohm series resistor, but I still think it's been ok. I didn't see ANY problems that I did not also see with a standard 78S05.

John Popelish wrote in news:M_ydnWTbPsJp8b7bnZ2dnUVZ snipped-for-privacy@comcast.com:

OK, you got it. :) I just pre-empted that in the last post before I saw this..

John Popelish wrote in news:M_ydnWfbPsIQ8L7bnZ2dnUVZ snipped-for-privacy@comcast.com:

Agreed. This is one point I need to suss out, while the offset is small, it will be bigger than the op-amp's own offset, as it uses the 10M resistor like a long lever with a fulcrum close to the op-amp input.

As far as I know, the only thing that could seriously affect this is a significant change in the 24V supply. I never saw such, I specifically looked for that. It would have had to change in obvious step with DMP display updates, it would have been a clue as obvious as a slap in the face, and it wasn't there.

I'll still look into this as a possible source of error, if it doesn't counteract the op-amp's own thermal drift. None of which is ultimately bothersome though, I'll probably arrange to set for zero before any critical measurements are made. Small drifts are fine, if I'm monitoring anything long-term with this, I'll be controlling the ambient conditions for best stability anyway.