The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
Subject: Anyone had trouble with Allegro second-sourced motor drivers eg. ULN 20xx?
From: Geoff C
Date: Mon, 25 Nov 2002 03:36:38 GMT
NNTP-Posting-Date: Mon, 25 Nov 2002 14:36:38 EST
Allegro no longer make their quad darlington drivers ULN2068
amongst others. We use these to drive unipolar stepper motors
driven from INTEL 8255 ports in full stepping mode with a 24v zener
from the catch diodes to the 12V supply which is also connected to
the centre of each motor winding. Trouble is, I tried a Thomson
brand and it does not work correctly. It's hard to explain without
diagrams but here goes. The waveforms on coil "2" look perfect ie.
each end is monitored and they are 180 deg out of phase with 50%
duty cycle. The waveforms on coil "1" are not ideal. They have a
glitch in the on period which turns the driver off for about 1 ms
and similar in the on period. I am running the motors at about 70
ms waveform period. If I hold the motor shaft or try and help speed
it up the width of the glitch changes slightly. This leads me to
suspect that it is not a logic oreiented problem but possibly a
crosstalk problem or similar. I am sure my input waveforms have no
artifacts. The design is 15 years old and fault free until I tried
to change brands of IC. The local sales rep said that many complain
about non-Allegro brand IC's not working but I would like to know
why and design around the difference. If I can find a 50 volt rated
MOSFET array I might consider that too but have not been able to.
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup