Tranistor help

[andrew8485]

Hi, I am new to electrontics but have read some tutorials and have one question about a transistor the one I am looking at is jam #2n3903. Here is what I want to do. I want to put a cap before the base of the trasistor because the input will be pulseing this way it will be a constant flow of electric before it goes into the base. I know the base need 6 volts but the teck sheet does not tell me any thing else about the base requirements of the transistor so that I can figure out what size cap I need or can I find the size of a cap I need with just the voltage?

 

[panic mode]

2N3903 is general purpose NPN transistor. Like any Si-type NPN transistor, base voltage is ca. 0.6-0.7Volt (not 6V). Post your circuit
and explain what are you trying to do if you need more help.

 

[andrew8485]

thanks for your reply. when D=on it will be pulseating on off on off on off ect (like a turn signal) and so I put a cap after D so that while d=on it has consent power going into the base of the transitor that way I will get constant power out of the emitter ( and not on off on off on off). But when D=off there will be no power threw D so the cap will need to decharge with in 1-2 seconds so that the emitter will not emit power . Now what i am trying to find out is what size cap to put in. So in order to do that i need to find out how much current the base uses (If any ). Do you understand what I am trying to say. I don't have to use the ezact model transistor, but I have to use a transistor! If there are any more questions please ask thanks

 

[andrew8485]

How much amps does the base of the transistor use the model is jam # 2n3903
thanks

 

[Optikon]

How much amps does the base of the transistor use the model is jam # 2n3903
thanks

I didnt look at any datasheet but it sounds like 3903 is bipolar type.. so the amount of base current will be (Ic/hfe).. that is roughly, collector current divided by hfe (forward gain).. use this to estimate base current requirements. Oh, you should find some graphs with hfe in the datasheet.
Values of hfe ranging from 40-400 are common for small signal types.