I assume this question is very common, because I read a lot of answers here, but I still missing somthing..
I have "Electric Imp" module, which have max I/O pin power output of 4mA, and its run on 3.3V.
I need to run electric door, which consume 12vdc 500mA at max.
So i started and checked the 2N2222A transitor:
Ic(MAX) = 1A – good enough.
Vceo(MAX) = 40V – good enough
and now I am geting to the base needs (the gain):
in the Hfe I see that the closest is Ic=500mA, Vce = 10V (I need 500mA and 12V, so it is close enough), the gain for this will be 40, which means I need 500/40 = 12.5mA as output.. I do not have it.. am I right so far?
Another thing I am missing is – where can I see in the datasheet that 3.3V is enough on the base, BJTs is not Voltage , but current base, right?
if I am right so far, so I need 500mA/4mA = Hfe of 125, but I couldnt find such resistor.. I can add relay 12vdc coil with lower current than 500mA and use the NPN to run the coil so it will run the door lock..
Thanks, Gabi.
Best Answer
You are correct. With a gain of 40, the 2n2222A is not right for your limited current. There are four solutions.
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