Hello guys
How much is the value of the input resistance of the npn transistor "2n2222a"?
Does it change with the frequency?
Thank you

 

You need to better specify your question. Are you asking about the base current, and its impedance?

 

At which terminal is your 'input'?
The transistor junctions have inherent capacitance, therefore their AC impedance is frequency-dependent.

 

You need to better specify your question. Are you asking about the base current, and its impedance?

Hey wayneh
i mean the resistance between base and emmitter when the transistor is on

 

At which terminal is your 'input'?
The transistor junctions have inherent capacitance, therefore their AC impedance is frequency-dependent.

Hey alec
the input is at the base

 

Read

http://www.electronics-tutorials.ws/amplifier/input-impedance-of-an-amplifier.html

 

Hey wayneh
i mean the resistance between base and emmitter when the transistor is on

It's low! It's basically a diode and will conduct enough current to destroy itself if you don't control the base current. Look up the diode equation if you want to estimate how the "resistance" changes with current. Then look for information in the data sheet that may give you reference points on the diode curve.

That's a DC view.

 

Look up the diode equation if you want to estimate how the "resistance" changes with current.

http://forum.allaboutcircuits.com/blog/turn-on-voltage-of-a-bipolar-transistor-vbe-ic.571/