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Re: blowing up OPA277's

Newsgroups	sci.electronics.design
Subject	Re: blowing up OPA277's
References	<78326379-99a7-416d-bae8-8ef95bd98c01@googlegroups.com> <op.yqfmv5w1wei6gd@phenom-pc>
From	"David Eather" <eather@tpg.com.au>
Message-ID	<op.yqitgbsbwei6gd@phenom-pc> (permalink)
Date	2016-11-07 05:22 +1000

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On Mon, 07 Nov 2016 05:22:12 +1000, David Eather <eather@tpg.com.au> wrote:

> On Sat, 05 Nov 2016 04:28:14 +1000, George Herold  
> <gherold@teachspin.com> wrote:
>
>> Hi all, I'm prototyping this square root circuit. (I had a thread here  
>> maybe a year ago.)  The circuit works fine in spice, but turning it on  
>> and off a few times.. (or something) is causing the opamp protection  
>> diodes to fail.  (All of a sudden the inputs are spitting out DC  
>> voltages.)
>>
>> A circuit fragment looks like this,
>>
>>
>> Vin----RRRRR-----+----more of the same...
>>                  |
>>                 R1
>>                  |
>>                  +--|>|---+
>>                  | |\     |
>>                  +-|-\    |
>>                    |   >--+
>> V ref--------------|+/
>>                    |/
>>
>> I've found the OPA277's to be a little "delicate" in the past, is there
>> something bad about the diode in the feedback path?
>>
>> I'm going to try a different opamp type.
>>
>> Oh, I also use the similar OPA227... faster more Vos.
>> In the spec sheet for the opa227 they recommend a minimum resistance
>> of 500 ohms in the feedback path.
>>
>> George H.
>
> the diode means the OpAmp has to be stable at unity gain

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Thread

blowing up OPA277's George Herold <gherold@teachspin.com> - 2016-11-04 11:28 -0700
  Re: blowing up OPA277's Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2016-11-04 11:35 -0700
  Re: blowing up OPA277's bloggs.fredbloggs.fred@gmail.com - 2016-11-04 11:55 -0700
    Re: blowing up OPA277's George Herold <gherold@teachspin.com> - 2016-11-04 12:02 -0700
      Re: blowing up OPA277's bloggs.fredbloggs.fred@gmail.com - 2016-11-04 19:19 -0700
        Re: blowing up OPA277's George Herold <gherold@teachspin.com> - 2016-11-07 05:42 -0800
          Re: blowing up OPA277's DemonicTubes <tlackie@gmail.com> - 2016-11-07 09:08 -0800
            Re: blowing up OPA277's George Herold <gherold@teachspin.com> - 2016-11-07 10:35 -0800
              Re: blowing up OPA277's tabbypurr@gmail.com - 2016-11-07 11:54 -0800
      Re: blowing up OPA277's "John Miles, KE5FX" <jmiles@gmail.com> - 2016-11-05 21:30 -0700
        Re: blowing up OPA277's "P E Schoen" <paul@pstech-inc.com> - 2016-11-06 21:09 -0500
  Re: blowing up OPA277's Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2016-11-04 15:52 -0400
    Re: blowing up OPA277's George Herold <gherold@teachspin.com> - 2016-11-04 15:52 -0700
  Re: blowing up OPA277's Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> - 2016-11-04 18:26 -0400
    Re: blowing up OPA277's George Herold <gherold@teachspin.com> - 2016-11-04 15:59 -0700
      Re: blowing up OPA277's Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> - 2016-11-04 19:06 -0400
        Re: blowing up OPA277's George Herold <gherold@teachspin.com> - 2016-11-04 16:32 -0700
  Re: blowing up OPA277's "David Eather" <eather@tpg.com.au> - 2016-11-07 05:22 +1000

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