DIY_EFI Digest V5 #385

[944 Technologist]

Actually, you can not drive any op amp to the rails or anywhere near it. Typically you can not approach to within 2V of either power supply rail (V+ and V-). Any signal approaching the power supply  "rails" will go non linear and then clip well below the rail..

The LM324/ LM2902 series op amps are different. This is probably why it was selected for this application. The output can vary from V- to V+ -1.5V. For this application, with "battery ground"  and "battery ground" plus 5V as the rails for the LM324, the output can only vary from 0V to 3.5V. 

FR Wilk
_____________________________

>From: "Mike Martone" <mmartone at shore.intercom.net>
>To: <diy_efi at diy-efi.org>
>Subject: Re: DIY_EFI Digest V5 #385
>Date: Wed, 15 Nov 2000 13:43:21 -0500
>Reply-To: diy_efi at diy-efi.org
>
>hmmm... a 7805 on an LM324 (or 124 if ya want milspec) will only drive the
>opamp to a rail of about 4.75V... the 7805 is typically 4.95 on the output
>and ya won't see any more than that at the opamp's outputs... maybe a 7809?
>if you're really worried about driving too much into the 324 (which is way
>below the 38V SE or +/-18V bipolar before it fries value), throw a trimpot
>on the output of the regulator and adjust it to whatever suits ya......by
>the way... anybody know why they put a mirror behind the movement of a
>micronta VOM?
>
>have fun,
>meat head
>----- Original Message -----
>From: Barry Tisdale <btisdale at cybersol.com>
>To: <diy_efi at diy-efi.org>
>Sent: Wednesday, November 15, 2000 12:24 PM
>Subject: Re: DIY_EFI Digest V5 #385
>
>
>> Thanks for the truly definitive answer, Chad.  There's bound to be more as
>> this project progresses.
>>
>> Barry
>>
>> At 10:22 AM 11/15/2000 -0600, Chad Clendening wrote:
>> >1) The regulator really needs to be a 8 volt variety.  Even with a good
>op
>> amp,
>> >the 5 volt regulator didn't have enough headroom.  The V+2.5 and -2.5 are
>> not the
>> >actual voltages present.  It was more like v+3 and v-5
>> >The artificial ground isn't evenly split since more negative current is
>> needed
>> >than positive current.
>> >
>> >2) The early data was taken with a earlier prototype and the I to V amp
>> was wired
>> >differantly.  It was taken as a meter was laying around doing nothing.
>> >
>> >Chad
>>
>> --------------------------------------------------------------------------
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