piclist 1997\09\11\120849a >
Thread: Cheap Motor drivers [OT]
www.piclist.com/techref/io/motors.htm?key=motor
picon face BY : David W. Duley email (remove spam text)



In a message dated 97-09-10 16:44:12 EDT, you write:

<<
        You can build yr own H-bridge out of discrete transistors -- a
little more expensive than an appropriate IC at low power, but it is the
way to go for higher powers. An H-bridge is a really simple circuit --
it's somewhere in the Art of Electronics along with a complete discussion
of analysis and transistor selection. If you can code assembler, you can
certainly build an H-bridge.

        Pierce Nichols
 >>
Hello Pierce,
In theory the H bridge is simple, but the simplicity stops when you actually
try to build one.  Check out the circuit for the LM18245 from National.
It becomes very complicated when you try to use 5 volts to switch anything
greater than 5 volts.  If you turn on a Mosfet with 5 volts that is what you
get out of a P channel Mosfet.  The 18245 uses a DC/DC converter to step up
the control voltages.
If you are running simple 3 to 6 volt motors then I agree with you.  You can
kill alot of transistors trying to get one working though.
An H bridge, if not connected right the first time, will incinerate in a
fraction of a second.
Been there...Done that...

Dave Duley
V.P. DreiTek Inc.
http://www.dreitek.com
<970911120635_-332280165@emout04.mail.aol.com>

See also: www.piclist.com/techref/io/motors.htm?key=motor
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