Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
Subject: Re: Return current path and magnitude??
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Fri, 20 Sep 2002 10:01:55 +0100
NNTP-Posting-Date: Fri, 20 Sep 2002 10:01:57 BST
"Håkan" wrote in message
> This I think is quite obvius:
> An op-amp is connected to V+ and GND (0-Volt), then current flows from
> GND. Making GND current return path. The current flowing in GND can be
> large. Therefore, it is important in critial op-amp applications to
> that this current in GND traces is separated from low current GND
> Q: Now suppose, an op-amp connected to V+, V- and GND. Is GND still
> current return path?
If the load is at ground, although there will still be some bias current
flow from VCC to VEE.
>Then this would imply that the op-amp draw current from
> V+ to GND, which is as above. Wouldn't this also imply that current is
> from GND to V-, thus a negative current from V- to GND (or positive
> from GND to V- ;-) ). Thus resulting in an alternating current flowing
> through GND. Correct ???
> If it is so, how much current can be drawn from GND to V-? I have
> considered GND to be current source but rather a "black hole" that can
> "swollow" what ever current comming from real current sources, until
> the fuse.
The opamp, with no load, should only pass current from VCC to VEE. If
you have a load on the output connected to ground, then there will
obviously be a ground current. Sources and sinks are really an arbitrary
concept, so a ground can source current.
In a high performance design you would certainly want to keep the input
signal ground away from the output ground, e.g. by a star point.
A typical op-amp can source and sink 20ma to/from ground, some can do
several hundred ma.
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