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'[PIC]:Driving a relay? Must Be Doing Something Wro'
2002\01\28@003052 by Steve Kasm

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I have built the circuit below, when connected to the pic the relay
operates regardless of the pic pin being high or low. I have also
noticed that the relay energizes if I place the base through 2.2k
resistor to ground or vcc. Any suggestions?


Regards,
Steve

{Original Message removed}

2002\01\28@020851 by Jinx

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> I have built the circuit below, when connected to the pic the relay
> operates regardless of the pic pin being high or low. I have also
> noticed that the relay energizes if I place the base through 2.2k
> resistor to ground or vcc. Any suggestions?

Got the transistor hooked up in the correct orientation ?

Is it a good one ?

You could always sniff around for clues here

http://www.piclist.com/techref/io/relays.htm

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2002\01\28@132514 by Dal Wheeler

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It sounds like you may have the collector and emitter backwards...  What
transistor are you using?  You might try manually switching the base
resistor from ground to the 5v rail to see if you're getting the same
results...

{Original Message removed}

2002\01\28@152554 by Ted Mawson

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Here's a suggestion - use an FET which you can think of as a switch.
Try the BUZ11 which may be overkill but may even allow you to get rid of
the relay and drive the load directly!

Check out this link http://www.fairchildsemi.com/ds/BU/BUZ11.pdf

Connect the source to ground, the PIC output to the gate(s) via a
resistor, say 1kO, but that could probably be higher rather than lower
as the input impedance of the FET is so high that you can think of it as
a voltage operated device.  Connect the load or relay coil between V+
and the drain.

                        V+ (up to 50v)
                        |
                       Load
                        |
                        D
PIC O/P --/\/\/\/\----G
           1kO          S
                        |
                     Ground

The BUZ11 can switch 30A at 50V and the drive current into the gate is
so low that you could probably drive 100 of them from one PIC pin!  The
other cool (literally) thing about this baby is that the ON resistance
D-S is 0.04O so, even if you were pulling 10A through it, the power
dissipated would only be 4watts AxAxR with just 0.4v dropped across the
FET.

Hope this helps!

Ted Mawson
spam_OUTTed.MawsonTakeThisOuTspamPortfolioPM.com
http://www.portfoliopm.com


{Original Message removed}

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