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Old 2nd November 2013, 11:57 AM   #1
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Default Replacement for OPA2134 at DC Servo

I would like to ask your opinion in replacing OPA2134 for an LME49720 in one DC Servo application?
Technically wich one should do a better job?

Thanks for the help
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Old 2nd November 2013, 12:36 PM   #2
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See attached schematics of the application if needed.
I did replaced the opamp at the servo location with the lme.
Just to want to ensure that changed for a better one for the specific purpose.
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Old 2nd November 2013, 01:49 PM   #3
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Why would you put a 2134 in a servo application? A servo op amp should be optimized for DC operation. A 2134 is a favored amp for audio application.

Apples and oranges.

Since you replaced it, did you measure offset and drift before and after? That way you could answer your own question.
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Old 2nd November 2013, 01:57 PM   #4
Mooly is online now Mooly  United Kingdom
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The OPA should be the better of the two due to being FET input as you need minimal input bias currents. A TL071 is often the usual choice.
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Old 2nd November 2013, 02:00 PM   #5
sreten is offline sreten  United Kingdom
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Hi, and you don't need anything "better" than a TL071 or similar, rgds, sreten.

However the circuit appears to use dual op-amps, so the question is very misleading.
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Last edited by sreten; 2nd November 2013 at 02:02 PM.
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Old 2nd November 2013, 02:03 PM   #6
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Fast Eddie: it was already there, as its a branded product that I was trying to improve.
I dont have that much knowledge and Im trying to understand.

Moly: should the TL071 outperform the 2134 in there?

Thanks
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Old 2nd November 2013, 02:11 PM   #7
DUG is offline DUG  Canada
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How much offset will you allow?

According their respective data sheets:

Vio

OPA2134 +/- 2mV max
LME49720 +/- 0.7mV max
TL071 +/- 6mV max

That does not mean that they will be that much but it is what I would start looking at.
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Old 2nd November 2013, 02:46 PM   #8
Mooly is online now Mooly  United Kingdom
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The OPA should be fine as servo chip. No real difference between that and a TL071 for this application. You don't all the attributes that make a "good" audio chip. You need low input bias current which means FET input.
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Old 2nd November 2013, 02:55 PM   #9
Mooly is online now Mooly  United Kingdom
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Quote:
Originally Posted by DUG View Post
How much offset will you allow?

According their respective data sheets:

Vio

OPA2134 +/- 2mV max
LME49720 +/- 0.7mV max
TL071 +/- 6mV max

That does not mean that they will be that much but it is what I would start looking at.
Look at the input bias current for the LME49720. I think its 10 nano amp. Sounds small until you realise it would deliver a 100mv offset with a 10meg resistor at its input. The OPA with 5pa bias current would deliver 0.05 mv under the same condition. The TL071 would be a similar ballpark figure.
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Old 2nd November 2013, 05:30 PM   #10
00940 is offline 00940  Belgium
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Quote:
Originally Posted by sreten View Post
However the circuit appears to use dual op-amps, so the question is very misleading.
+1

From the schematic linked, it seems like the same dual opamp is used both as output buffer and servo. So we need an opamp able to fulfill both roles.

OPA2134 seems perfectly fine here.
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