How to Calculate the Base Current, IB, of a Transistor

base current, Ib, of a transistor

The base current, IB, of a transistor is a crucial current of a bipolar junction transistor. Without this base current, the transistor can't turn on.

There are several ways to find the base current, IB, of a transistor. And it all depends on what information is already known about the transistor:

1st Way To Calculate Base Current IB

DC Analysis

Doing DC analysis of the transistor circuit is the most common way of finding out the value of IB in the circuit.

How to calculate Ib of a Transistor Circuit


The equation to solve for Ie is:

formula to calculate the base current Ib of a transistor

So we must solve for Vbb and RB in order to solve for IB.

How to Calculate Vbb of a Transistor


Next we compute the value of RB:

How to Calculate RB of a Transistor

Now we can calculate the value of the base current, IB, in the circuit:

formula to calculate the base current Ib of a transistor

Example

Using the example of the values for the resistors and the voltage, Vcc, above, we're going to solve for Ieq.

Vbb of a Transistor

Rb of a Transistor


solving for base current ib of a transistor

2nd Way to Calculate Base Current IB

Using Known Values
If the emitter current, Ie, and β are known for the transistor circuit, IB can be calculated by the formula:

base current ib formula with beta

Example
If Ie=6ma and β=99, then

solving for base current ib example

3rd Way to Calculate Base Current IB

Using Known Values
If the emitter current, Ie, and the collector current, Ic, are known, IB can be calculated by the formula:

How to calculate base current Ib using emitter current Ie and collector current Ic

Example
If Ie=4ma and Ic=3.96ma, then IB calculates out to be:

Example of calculating base current Ib using emitter current Ie and collector current Ic


Related Resources

How to Calculate the Collector Current IC of a BJT Transistor

How to Calculate the Emitter Current IF of a BJT Transistor

How to Calculate β of a BJT Transistor

How to Calculate α of a BJT Transistor

How to Calculate VBB of a BJT Transistor

How to Calculate VCE of a BJT Transistor

How to Calculate Vπ of a BJT Transistor

How to Calculate Rπ of a BJT Transistor

How to Calculate GmVπ of a BJT Transistor Circuit

How to Calculate GM of a BJT Transistor



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