Im working on a project that uses an electronic door lock. It needs a lot more power than an arduino can supply, so my thought was to use a transistor to switch on a second power source solely for the door lock. I've been trying to figure this out for hours. I thought transistors were just electrica…

TIP31A Transistor Help

Grumpy_Mike November 22, 2011, 11:10pm 9

but I'm not sure how to choose the resistor on the base.

Choose it such that the base current is at least the collector current divided by the transistor's gain. Then give it a bit of margin by halving it.

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