PIC driving a relay
Harold Hallikainen email (remove spam text)
I've got an application where I need to drive a relay with the
PIC. To keep the parts count down, I'd like to do it with no additional
parts. The relays available have a 5V, 30mA coil or a 12V, 13mA coil.
The 30 mA looks like more than can be driven with a single output pin.
If i go to the 12 V relay, the current is ok. What is the maximum
voltage on the RA4 open drain pin? Can it go that high (or higher)? Of
course, I'd have to add a clamp diode to protect the chip when the relay
is shut off. I cannot find the maximum voltage rating on the RA4 output
in the Microchip documentation (this is on a 16c74a).
Another possibility is to just use two I/O lines in parallel and
turn them both on at the same time. Seems like this could drive the 5V
relay. Also, the internal clamp diodes could probably protect the chip
from the relay, right?
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm
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See also: www.piclist.com/techref/microchip/ios.htm?key=relay
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