BC547 v/s 2N2222 transistor

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rahulrox1991

Joined Oct 31, 2011
16
I have a small circuit which controls the speed of a DC motor as per the ambient temperature. The circuit is working perfectly fine. I have across this circuit across a lot of forums and was just wondering if I could replace BC547 (Q1 in the circuit) with the commonly used 2N2222 npn transistor.

I checked out the SPICE simulation of the circuit and power dissipation isn't an issue (which usually is under most circumstances for NOT using 2N2222). Any other reasons that you could suggest.

Here is the circuit diagram - http://www.redcircuits.com/Page109.htm
Thanks in advance :)
 

Thread Starter

rahulrox1991

Joined Oct 31, 2011
16
have you looked at the datasheets?
Yes I did... 2N2222 has a maximum permissable power dissipation of 250mW whereas BC547 can take 500mW. But the circuit is operating in 4-12mW range for Q1 transistor. So thats not a problem. Any other problem that you could think of?

Any possibilty of temperature sensitivity? Since this circuit involves temperature control?
 

chrisw1990

Joined Oct 22, 2011
551
the only real place i can see where its lacking is the gain. everything else its surpassing the bc547.. :)
id try it.. see how it works.. the gain of the 547 might be crucial to the circuit
 

Wendy

Joined Mar 24, 2008
23,415
And the maximum dissipation for a metal cased 2N2222A is 600mw. You are looking at the plastic varieties.

When it comes to thermal conduction, metal always beats plastic. Many plastic 2N2222A are labeled PN2222A.

It is also possible to glue very small heat sinks on a transistor to increase its wattage, say a small piece of flat metal ¼" by 1/8 on the flat spot.
 

Ron H

Joined Apr 14, 2005
7,063
And the maximum dissipation for a metal cased 2N2222A is 600mw. You are looking at the plastic varieties.

When it comes to thermal conduction, metal always beats plastic. Many plastic 2N2222A are labeled PN2222A.

It is also possible to glue very small heat sinks on a transistor to increase its wattage, say a small piece of flat metal ¼" by 1/8 on the flat spot.
The NPN in that circuit is coasting.
 

Felo

Joined Feb 20, 2012
91
When I come across a replace for a switching transistor, I always choose over-kill so for this, 4401 would be my choice.
 
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