Hello David,  If you have long wires to your motor (>10 feet or so) you
should put diodes right at the motor.  The reason is the long wires have
both inductance and capacitance and will ring (oscillate) and your diodes
back at the driver will not block both polaritys.  Also watch thoes 4000
series diodes; you might be safer with 1N914 or 1N4148's as they are faster.
Bye,  Mick
----- Original Message -----
From: "David P Harris" <dpharris@TELUS.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, November 29, 2001 3:31 PM
Subject: Re: [EE]: Stepper motor control -L293D w/diodes ?


| Hi-
| I am unsure.  The datasheet shows internal protection diodes, but also
states
| that external diodes should be used.  "External
| high-speed output clamp diodes should be used for inductive transient
| suppression."  See: http://www-s.ti.com/sc/psheets/slrs008a/slrs008a.pdf
|
| Maybe someone with 'real-life' experience could comment.
|
| David
|
| "Kevin A. Benedict" wrote:
|
| > Hi,
| > I am driving two stepper motors (6.5v 350ma) with a f84a connected to
two
| > L293D chips.  Should I have diodes in the circuit to prevent back emf
from
| > the coils to the L293d chips ? If so can you recommend one ?  The
circuit I
| > am using does not have any.
| > http://www.seattlerobotics.org/encoder/may98/steppers.html
| >
| > Thanks in advance,
| >                 Kevin
| >
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