Subject:
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Re: lego cap, polarity, etc
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 28 Mar 2001 00:21:46 GMT
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Original-From:
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Jim Choate <ravage@einstein.SAYNOTOSPAMssz.com>
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Viewed:
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755 times
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On Tue, 27 Mar 2001, Bruce Boyes wrote:
> Right, what I was trying to say is that a bridge can't 'invert' a DC input
> of one polarity to make an output of another polarity - it can't "correct"
> anything, a diode can only conduct or not conduct. All a bridge can do is
> route the given DC input through one leg or the other of the bridge.
A couple of comments on this...
An 'inverter' with respect to DC creates AC, it doesn't swap polarity. If
you're going to use the term correctly always use 'invert polarity' and
never 'invert' by itself. If you go into a store and ask for a 'DC
Inverter' you'll get a black box that makes AC (usually a filtered square
wave) as output.
'Ground' per se is relative. So in many cases to make -5V out of +5V
you've only got to swap the ground and Vcc. This may or may not be
compatible to the rest of your electronics (hint: don't connect 'grounds'
from two dissimilar circuits because you create a short between the
rails). If you do this sort of stuff then you want to 'isolate' or 'float'
the connections (ie make them relative and not absolute). This is easy
with AC, use a transformer. One way to 'invert' the polarity is to drive a
chopper circuit (eg a 555 in free-run mode), run it into a transformer to
isolate it, and then signal condition (ie integrate and filter) the
resultant to the polarity you want. It's a current hog. You can also use
circuits like a PLL or Gyrator to create AC and then condition that. In
any case, if you need more current then the chopper can deliver then put a
big old power transistor across the rails and drive it from saturation to
cut-off with the xfrmr as the load.
____________________________________________________________________
If the law is based on precedence, why is the Constitution
not the final precedence since it's the primary authority?
The Armadillo Group ,::////;::-. James Choate
Austin, Tx /:'///// ``::>/|/ ravage@ssz.com
www.ssz.com .', |||| `/( e\ 512-451-7087
-====~~mm-'`-```-mm --'-
--------------------------------------------------------------------
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Message is in Reply To:
 | | Re: lego cap, polarity, etc
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| (...) Right, what I was trying to say is that a bridge can't 'invert' a DC input of one polarity to make an output of another polarity - it can't "correct" anything, a diode can only conduct or not conduct. All a bridge can do is route the given DC (...) (24 years ago, 27-Mar-01, to lugnet.robotics)
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