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Relay question (adding relay to Oscars LED driver board) - it works!
RandyT:
--- Quote from: JoyMonkey on June 15, 2005, 10:46:09 pm ---Could it be the transistor I'm using? I just used what I had at hand (a PNP to 92 transistor 2N3906) which is different to the one's that Oscar uses in the LED driver circuit, but he does say that any general purpose PNP transistor should do.
What happens if I take the 1k resistor out of the equation?
--- End quote ---
The relay doesn't take much power to actuate it, so I don't think it's the transistor. The 1k resistor should stay in place as well.
About the only thing I can think of to do at this point is swapping the A and B connections. I know a coil doesn't care about polarity, but the diode across the contacts throws in something different that I'm not fully versed in. The way it's wired right now, the diode appears that it would be conducting, which might be creating a short circuit. If you wire it the other way, current should only be able to flow through the coil.
Remember, "AS IS" info :)
RandyT
JoyMonkey:
I'll try flipping the diode around tonight. Thanks!
(I wish I made this thing on a breadboard first)
JoyMonkey:
I removed the diode and the relay is working great now!
I haven't had the chance to put it back on in the opposite position, but do I really need it?
RandyT:
--- Quote from: JoyMonkey on June 16, 2005, 05:42:04 pm ---I removed the diode and the relay is working great now!
I haven't had the chance to put it back on in the opposite position, but do I really need it?
--- End quote ---
No clue. You probably want to ask the guy who designed the circuit ;)
I'm pretty sure it was there to protect the other circuitry from spikes and such. I'd flip it around and put it back just in case. It isn't huting anything by being there, you just had the polarity reversed..
RandyT
ShinAce:
Flip it around, make sure it works in that position, and leave it there.
The coil is an electro-magnet, and having a current through it "energizes" it, or creates a magnetic field. When you suddenly stop the current, the field collapses, creating a current. This back EMF consists of a big single spike. The diode just acts as a mini surge suppresor.