Hi,
I have a pic driving the base of an NPN through a 1k resistor.
One end of a relay coil going to 12V and the other end going to the collector of the NPN. These are diode relays, but I'll get to that.
The emiter of course goes to ground.
Anyway, I turn the pic output high and the relay siwtches.
Now, my problem is that someone hooked the relay up in reverse so that the diode inside was going the wrong way. Now, what I "think" was happening was that when I triggered the relay, 12V went down through the diode and not the coil, into my transistor where it was connected with ground. Shorted.
I wasn't around but I beleive the relay never fired, so it was not a EMF problem.
Would that blow an NPN?
Obvious choice would be to put a resistor inline on the collector to prevent this from happening again, but I'm not sure about what size, too small and it will just blow the resistor (i hate fuses) and too big will stop the reay from working no ?
Thanks
I have a pic driving the base of an NPN through a 1k resistor.
One end of a relay coil going to 12V and the other end going to the collector of the NPN. These are diode relays, but I'll get to that.
The emiter of course goes to ground.
Anyway, I turn the pic output high and the relay siwtches.
Now, my problem is that someone hooked the relay up in reverse so that the diode inside was going the wrong way. Now, what I "think" was happening was that when I triggered the relay, 12V went down through the diode and not the coil, into my transistor where it was connected with ground. Shorted.
I wasn't around but I beleive the relay never fired, so it was not a EMF problem.
Would that blow an NPN?
Obvious choice would be to put a resistor inline on the collector to prevent this from happening again, but I'm not sure about what size, too small and it will just blow the resistor (i hate fuses) and too big will stop the reay from working no ?
Thanks