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#2n3055 transistor linear response bias series
If it were I designing this circuit, I'd use a 4.7K Onm resistor in series with the base of the 2N2222 transistor and a 1K Ohm resistor in series with the collector of the 2N2222. So, set the 2N2222 to a gain of about 30 and the 2N3055 to a gain of 10, equaling a gain of 300. The 2N2222 will have a gain of about 100, and the 2N3055 is maybe 10. The relay coil requires say, 3.1 amp, and the device driving the base of the 2N222 is say, 10ma. You have to determine the current gain required - G = Iout / Iin. I hope that I didn't mess up in the calculations (peer review!? :)) Hope that it sheds some light though! Here you're on the safe side, but as you said you can feel the transistor getting a bit warm. II: (R1 = 2,2 k) Same calculations gives Pd = 1,85 W. Pd will then be 11,3*0,3 = 3,39 W and the transistor is history. The current through R1 will then be 3 mA which in turn gives a collector current of 300 mA (hFE = 100). I: (R1 = 1,2 k) At the base of 2N2222 there will be roughly 1,4 V (~0,7 V across each base-emitter junction) which will, when the uC output is set to 5 V, give 3,6 V across R1. Using this as a guide we can calculate the power dissipation for the different cases you've tried.
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If you look at you're circuit you will have when the 2N2222 is "ON", about 11,3 V across it (collector - emitter). The data sheet I have says Pd(max) = 500 mW. You're circuit looks ok, but you're problem is due to the fact that you're exceeding the 2N2222's maximum rated power dissipation. I really need a proper schematic as I am really lost and have tried for two days to figure it out.
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If somebody could help me with this I would be greatly appreciative. Would someone be so kind as to offer me a schematic with resistor values that will work.Ĭoil 4.72 ohm 12.5 to 14.5 volt (car electrical supply), which I assume draws around 3 amp. Obviously, I am no electrical engineer!! just a simple hobbyist having a go. I have tried several different resistors on the base of the 2N2222 (values based on formula's from the Net) but it keeps getting hot and blowing. I have a 2N2222A and a 2N3055 which I was going to hook up as a Darlington Pair to protect the micro (good idea, yes/no?). What I am trying to do is turn a coil that draws 3.10 amps on and off using a port of a Mega128. I have also cooked 4x 2N2222's as well, one for each different answer. I have scoured the Net for ways to make this work and seem to get different answers. Hi All, Could I please have your invaluable advice.