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Re: NPN and relay

Posted: Fri Dec 28, 2018 11:47 am
by David
You can't just replace a NPN transistor with a PNP one (and vice versa) and expect it to work. The circuitry would need to be changed to accommodate the altered polarity. You will need to find out the chacteristics of the faulty transistor (current and voltage handling, gain and dissipation are the main ones) are and get a similar tranny. The diode goes straight across the relay coil, connected so that it is reverse biased when the relay is powered.