cceto1

I have what I hope is a simple question that I can't seem to
find an exact answer to. I am starting to learn electronics
and circuits, and have been playing with some microcontrollers.

Here is my question.Let's say I have an output off of one of the
pins of my microcontroller at Vcc which is 5 volts DC. I want to use
that output to connect to the coil of a relay. However, that requires
12VDC to activate the relay. It seems simple enough, but how
do I bump up the voltage from 5V to 12V ? I was looking
at the Wall PF5S12-84 IC, which seems to do this. However, am
I making this too complicated? Is there a better/simpler/smarter
way? Or perhaps it is as simple as a few common components
wired together to perfrom the magic.

thanks for any insight you may have!

chris

Nigel Goodwin

You use an NPN driver transistor, emitter to chassis, base to micro via a resistor, and collector to the relay - you MUST fit a reverse biased diode across the relay coil to avoid blowing the transistor.

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cceto1

I want to try to understand this. So in this case, the 5V from the
microcontroller will provide current to the base of the
transistor. That will then turn on the switch and allow current
to flow to the coil. So, in this case, the collector attaches to one
lead of the relay coil, and the other lead of the relay coil attaches
to a seperate 12V supply voltage. Is this correct? In other words,
this will not increase the 5V from the microcontroller to 12V, I am
simply supplying a seperate 12V feed? Am I way off on this one?

chris

Nigel Goodwin

That sounds about right, there's a diagram I posted previously at http://www.electro-tech-online.com/download.php?id=1765, have a look at that.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk