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Electronics => Electronics => Topic started by: TrickyNekro on August 28, 2008, 07:53:15 AM

Title: Need transistor math and theory
Post by: TrickyNekro on August 28, 2008, 07:53:15 AM
Hello guys,


Same as title.... on both PNP and NPN transistors...
I found some NPN calculators but nothing more...

I need to build some transistor based circuitry and I want to calculate some resistor values
although I can place them based on experience, cause I'm dealling with more than one or two transistors...

Hope you can help,
Best Regards, Lefteris
Greece
Title: Re: Need transistor math and theory
Post by: benji on August 28, 2008, 10:27:37 AM
whats the circuit ya wanna builld?
Title: Re: Need transistor math and theory
Post by: ArcMan on August 28, 2008, 12:58:22 PM
Try out this site:

http://www.allaboutcircuits.com/vol_3/index.html (http://www.allaboutcircuits.com/vol_3/index.html)
Title: Re: Need transistor math and theory
Post by: TrickyNekro on August 28, 2008, 06:10:31 PM
Quote from: benji on August 28, 2008, 10:27:37 AM
whats the circuit ya wanna builld?

Well, just for effect I want to place a bidirectional LED on the RESET line of my micro...
When micro is working LED would be green, but when programming or reseting it would be RED

I came with a circuit of four transistors and I'll upload the schematics soon enough!!!
I only want to calc some resistors before testing.... so that I don't burn 'em...
Not that they cost me something only time getting downtown to buy new....


Anyways, thank you both for the interest!!!
Best Regards, Lefteris
Title: Re: Need transistor math and theory
Post by: benji on August 29, 2008, 04:37:41 AM
as long as you want it to be only a switch the math would be easy...

the BC547 is widely used  in switching
Title: Re: Need transistor math and theory
Post by: RobD on August 29, 2008, 11:28:09 PM
Transistor Bias....

Three letters - PNP - "positive negative positive"

1.  The first letter P =  "positive emitter"

2.  Second letter N = "negative base"

3.  Third letter P = "emitter more Positive than the base"

It's the opposite for NPN's  ( for example - 3.  base more positive than emitter)