I'm having trouble figuring out what resistor I should use on base when wiring up a NPN transistor.
So, everything runs at 5 volts. The maximum current a 3904 can handle is 100ma, so is it okay too choose a resistor for a 100ma current so anything I hook up will work as long as it takes less than 100ma?
I was poking around and found that there is a voltage drop of about .6v. So say if the transistor has a gain of 50 (not sure what the 3904 has), and I want 100ma. So I would need a 2ma current to base. So using ohms law with 4.4 volts and 2ma, I get 2200 ohms. So a 2200 ohm resistor should work with any load up to 100ma- I think.
Now how do I find the gain of the transistor in the datasheet? I am looking at this one:
http://www.fairchildsemi.com/ds/2N/2N3904.pdf
Thanks!
So, everything runs at 5 volts. The maximum current a 3904 can handle is 100ma, so is it okay too choose a resistor for a 100ma current so anything I hook up will work as long as it takes less than 100ma?
I was poking around and found that there is a voltage drop of about .6v. So say if the transistor has a gain of 50 (not sure what the 3904 has), and I want 100ma. So I would need a 2ma current to base. So using ohms law with 4.4 volts and 2ma, I get 2200 ohms. So a 2200 ohm resistor should work with any load up to 100ma- I think.
Now how do I find the gain of the transistor in the datasheet? I am looking at this one:
http://www.fairchildsemi.com/ds/2N/2N3904.pdf
Thanks!