I just assembled a circuit which has a transistor to switch the coil on a relay (driven from logic level of microcontroller). The transistor is a general purpose TO92 package, 0.5 A switching type (like a 2N2222 or similar).
I had a problem with it that I've seen on odd occasions in the past. Every now and then I seem to get a leaky transistor that doesn't shut off properly. (I always have a diode in parallel with the relay coil to shunt the 'back emf' when the coil is switched off - to avoid damaging my transistors).
I've also seen this problem in other switching applications (not relays).
Am I getting my transistors too hot when I'm soldering, or is there something I should be looking out for to avoid this problem?
Cheers Glenn