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Voltage at the base of a transistor when a current source is connected to it

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Vijay Vinay

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Hi,
I have connected a current source to the base of the transistor, with Iref as 2mA. Now, I would like to know the value of voltage of the base of the transistor. Could anyone help me in finding it. Is there any particular formula for finding it out. In am getting the value of that voltage to be 1.95V. How is it so? Thanks in advance

work.jpeg
 

The datasheet for most transistors shows a graph of base-emitter voltage with different currents and temperatures.
Your schematic does not show a negative supply or a ground.
 

Hi RobertFalbo,
Could you elaborate a little bit on how its 0.6V more than the emitter voltage. Thanks in advance
 

Hi guys,
sorry Iref is 4mA. My mistake
 

Vijay Vinay said:
Could you elaborate a little bit on how its 0.6V more than the emitter voltage.
Click to expand...
You can read about the physics that causes it on the internet.
Almost every transistor datasheet has a graph showing the base-emitter voltage at different currents and at different temperatures. For a silicon transistor it is from about 0.6V to about 0.8V, averaging 0.7V.
 

Audioguru said:
You can read about the physics that causes it on the internet.
Almost every transistor datasheet has a graph showing the base-emitter voltage at different currents and at different temperatures. For a silicon transistor it is from about 0.6V to about 0.8V, averaging 0.7V.
Click to expand...

I know that Vbe is 0.7V, but RobertFablo has mentioned that the base voltage is 0.6V more than that of the emitter voltage. I need to know how its possible and why is it so?
 

As Audioguru said, you did not show the reference for that measurement, therefore we don't know if the 1.95v "base voltage" you mentioned refers to the Vbe of the transistor.
 

Vijay Vinay said:
I know that Vbe is 0.7V, but RobertFablo has mentioned that the base voltage is 0.6V more than that of the emitter voltage. I need to know how its possible and why is it so?
Click to expand...

I guess, with 2 ma base current you would be closer to 0.7 volts above the emitter voltage.


The typical voltage drop of a PN junction (diode) for silicon is, as stated above, 0.6 to 0.8 Volts.
 

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