I would like to ground an NPN emitter to the pin adjacent to it's base.
I would like to ground an NPN emitter to the pin adjacent to it's base. Is this a bad idea? The NPN's function is to open a 12v solenoid.
The base of an NPN transistor NEEDS a current limiting resistor.Base current for full saturation of the 'switch' should be 5-10% of the collector current, depending on the transistor.If that's more than ~20mA, then you should switch to a darlington or mosfet.
A TIP120 is a good choice for a solenoid.It still needs a base resistor, but base current for that darlington is 1:250 for saturation.Note the higher BE voltage (~1.5volt) when you calculate the base resistor.Don't forget the back-EMF diode across the solenoid.Leo..
The thing about a Darlington Transistor is the fairly high Emitter Collector saturation voltage. A MOSFET is a much better choice.
Not much difference if you power a solenoid with 11.25volt (darlington) or 11.95volt (fet).Different story if you switch a LED strip.Then a 1volt drop could have a light power reduction of 40%.Leo..