EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: radhika on August 28, 2018, 10:44:52 am
-
Hello,
I am working on current amplifier and I want 2A as a output from 250mA Arduino Input.
According to the transistor 2N3055 Ib = 40mA for Beta = 50
For getting 2A as a output from 2N3055 I have to get Ic = 80mA at 2N2222 and Rc = 50 ohm also, Ib = 40mA at 2N3055. But I can't get the required output.
I get 2A at Rc = 10 Ohm at 2N2222 and 10Ohm is so small. I don't have this small resistor. Can It be possible to get 2A for normal Ohm ( 22 Ohm to 10K Ohm ).
P.S. I am new to electronics. (https://postimg.cc/image/c4x1d5wzb/)
-
I would like to remind you that you can use 2x 22 ohm resistors in parrellel for 11 ohms,
I would say if you just want to switch 2A, a suitably sized mosfet may be better suited, but if All you have is a 2n2222 and a 2n3055, then sure, lets get it switching,
the 2n2222 has a beta (current multiplication more or less) of atleast 100, so for every 1mA in, you get 100 through the transistor,
the 2n3055 has a beta of atleast 20,
Lets say we hook them up as a darlington pair, this will drop some voltage, but will make it easy to get the amount of current,
So to switch 2A with the 2n3055, you need atleast 100mA into its base, so your 2n2222 needs atleast 1mA into its base,
https://www.kitronik.co.uk/blog/how-a-darlington-pair-transistor-works/ (https://www.kitronik.co.uk/blog/how-a-darlington-pair-transistor-works/)
-
https://postimg.cc/image/c4x1d5wzb/ (https://postimg.cc/image/c4x1d5wzb/)
This is the Darlington pair I have used
-
Should probably be more like this.
-
Hello,
Thank you so much for guidance. It really helpful. And I even got the result for 1A. Now, I am working on 2A too.
But I have a question. i.e. 2N3055 outputs at VCE = 2V. And in my circuit their is no resistor to get Vce 2V. Is this make it unstable?
Also, if I make Vce = 2A then, Vcc - Vce - IcRc = 0, so, (5-2)/1A = 3 Ohm. Hence it again give me 3Ohm which is so small. How do I solve this problem?
-
When you feed lets say 3.3V into the resistor, the 2n2222 will drop 0.7V across its base-emmitor junction, and the 2n3055 will drop an additional 0.7v to ground,
So your 2n2222 base will be at about 1.4V, and the 2n3055 collector will be at about 0.7V because its limited by the base-emmitor junctions voltage. this is a limit inherent to darlington pairs.
If you want close to a 0V drop, it would require something like an N channel mosfet,
-
Thank you so much Ma'am/Sir I will take care of it. You really help me a lot :)