Newsgroups: comp.robotics
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From: seeker@indirect.com (Stan Eker)
Subject: Re: SCR's for driving on/off functions.
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Date: Fri, 2 Jun 1995 08:22:52 GMT
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Aren Sandersen (aren@wolfe.net) maundered:
: Can SCR's be used for driving motors for a simple on/off?  Probably
: somewhere around 10 amps or so, at 12 volts.  If so, can these be used
: in an H-bridge format, do they need resistor biasing, etc.  What are
: the pin names?  (some SCR's I bought have the initials K A G -- which
: are which?)

normal SCRs are *only* useful in AC power, not DC, because once you turn
them ON, you have to remove the voltage across them to turn them off.  Oh,
they're used for power-supply crowbars and the like, sure, but generally NOT
as DC motor drivers.  The GTO (Gate Turn-Off) stuff would probably work, but
it's more expensive and harder to get in the hobby market than a good MOSFET
is.

: Is there a better device than a SCR to do this?

For general use, power MOSFETs are prime candidates because of the low on-
resistance.  Second choice is bipolar transistors.  They're second because
they dissipate more heat than an equivalent MOSFET, although they're simpler
to build an H-bridge out of (no high-side driver required).

Additionally, if you haven't looked there yet, check out the comp.robotics
FAQ in section 18.10.


