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Отправлено
M16C 22 февраля 2002 г. 19:39 |
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Привет всем!
Привожу тут фрагмент из форума на Филипс (см. ссылку Subject: DC Motor Drive)
Имею схожую проблему на 87C552.
При отключении реле сбрасывается MCU.На реле переменка.Диод воткнуть не могу.На старых 87C552 такого не наблюдалось.
Если у кого есть конструктивные предложения или полезные ссылки,
буду очень признателен.
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Dear Lipnharski
I got a problem.
I have to drive a DC 30 volts motor using a relay connected to the
microcontroller AT89C2051.
If I run the system without motor then every thing works fine. All relays
work properly.
The connection between the microcontroller and the relays are opto coupled.
There is complete
isolation.
However when I connect motor with the relay then the system starts giving
errors. It happen only
when the
relay turns motor off.
I have used surge protetors and snubbers at the power supply of the
microcontroller.
The power supply of the motor is absolutely seperate.
Do I have to use some snubbers at the motor supply also.
Please reply
-----------------------------------------
Dear Forum,
If the power supply for the motor circuit is completely
isolated from the supply to the uP I can see two possible reasons
for your errors. One, the sudden collapse of the mag field around
your motor is interfering with the control electronics ( processor
etc ). A test to see if this is your problem would be to connect a resistor of
suitable value in place of the motor. If no errors occur it would
suggest that the mag field is a problem. Solution, screen the
electronics or place the motor in a location remote from the
electronics.
Two, if the supplies are indeed separate there is no possibility of feed
back from the motor, but it may be coming from the relay coil or
contacts. Placing a reverse bias diode across the coil (if
possible ) and driving the coil using a MOSFET should eliminate this
problem.
Yours,
Paul F.Curtin
Microprocessor Systems Engineer.
-----------------------------
Dear Babar,
Your problem is sparks over your relay contacts that are caused
by the inductance of the motor. The electromagnetic field that
is generated disturbes your system. There are several ways
to solve this problem, I'll show two:
1 Place a snubber (for example 100 ohm + 100 nF) over the relay
contacts. This will damp most of the peak, the motor still
stops fast.
2 If the motor is sent in one direction only (only one voltage
direction), place a diode over the relay contacts. This will
cause the motor to stop slowly!
If this doesn't help, send more info with:
motor current, motor inductance.
Kind regards,
Pieter Hoeben, Electronics/software/firmware consultant,
Design of all kind of electronics and software.
Hoeben Electronics
Ronkert 44
5094 EW Lage Mierde
The Netherlands
Phone: +31 13 5096024
Fax: +31 13 5096025
E-mail: hoeben@bigfoot.com
-------------------------------------------
Dear Babar,
Are you by any chance using a TL7705 Supervisor IC to generate your =
reset signal?
I have had some bad experiences using this supervisor IC in several =
applications where I used a 8051 Board in a machine where I had to =
control 380V motors. In these applications I used a 8051 board which =
controls a 24V DC Relay, which in turn controlled a 380V power relay. =
The line to the 24V DC Relay was optically isolated and also all power =
lines were filtered and absolutely clean. The power relay was located at =
least 40cm from the 8051 board and the 380V motor was located outside =
the full-metal housing which contained the 8051 board.
When I disconnected the motor there were no problems whatsoever. But =
when I connected the motor the TL7705 started to generate reset pulses =
for no apparent reasons. I then examined all power supply, ground and =
signal lines connected to the TL7705 using a high-speed oscilloscope. I =
could not detect any glitches or surges that should cause the problem.
I then removed the TL7705 and installed a simple RC network to generate =
the 8051 Power Up reset. And guess what: All problems solved. Finally I =
redesigned the PCB to fit a MAX690 supervisor. This also works fine.
Up to now I cannot figure out why the TL7705 is causing these problems. =
I'm 100% sure the design was Ok. Also ground planes etc. on the PCB were =
Ok.
The only thing I can imagine is that the TL7705 was picking up some =
electromagnetic interference which caused the problems. Funny thing is =
that the TL7705 seems to be the only copmponent affected by this =
interference.
Hope this gives you something to work with ...
Regards,
Jan-Peter Groeneweg
jpgroeneweg@csi.com
E-mail: 
info@telesys.ru