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Old 12th November 2004, 02:28 PM   #1
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Location: Toronto, Canada
Default LMxxxx chip as a buffer inside feedback loop?

hi guys,

i just wanted to know if anyone has used the lmxxxx series of chips inside a feedback loop as a buffer with a opa627 (or slower chip) as the main opamp?

Is this even possible or is the lmxxxx not stable as a buffer?

Thanks,
300_baud
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Old 12th November 2004, 03:47 PM   #2
Sheldon is offline Sheldon  United States
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Default Re: LMxxxx chip as a buffer inside feedback loop?

Quote:
Originally posted by 300_baud
hi guys,

i just wanted to know if anyone has used the lmxxxx series of chips inside a feedback loop as a buffer with a opa627 (or slower chip) as the main opamp?

Is this even possible or is the lmxxxx not stable as a buffer?

Thanks,
300_baud
Unstable at gain less than 10.

Sheldon
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Old 12th November 2004, 04:44 PM   #3
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Location: North of Toronto
Small correction here: opa627 is unity gain stable but 637 needs gain =/> 5 according to the data sheet.
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Sheldon D
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Old 12th November 2004, 06:08 PM   #4
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Join Date: Mar 2003
Location: Lisbon, Portugal
Default Re: LMxxxx chip as a buffer inside feedback loop?

Quote:
Originally posted by 300_baud
i just wanted to know if anyone has used the lmxxxx series of chips inside a feedback loop as a buffer with a opa627 (or slower chip) as the main opamp?
OPA541/8/9 chips are stable at gains of 1.
But to include anything inside the feedback look of a signal op-amp it should be as fast or faster.
Power op-amps are (much) slower than most signal op-amps.
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