NPN and relay

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David
Posts: 189
Joined: Sun Oct 04, 2015 6:18 pm

Re: NPN and relay

Post by David » Fri Dec 28, 2018 11:47 am

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.

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