How to Calculate the Emitter Current, Ie, of a Transistor

Emitter Current of a transistor

The emitter current, Ie, of a transistor is the amplified output current of a bipolar junction transistor.

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

1st Way To Calculate Emitter Current Ie


DC Analysis

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

Emitter Current Ie DC analysis


The equation to solve for Ie is:

Equation formula of emitter current Ie in a transistor

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

The value of Vbb is computed by:

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 emitter current, Ie, in the circuit:

Equation formula of emitter current Ie in 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

current emitter ie example

2nd Way to Calculate Emitter Current Ie


Using Known Values
If Ib (the base current) and β are known, Ie can be solved for by using the formula:

Ie formula of a transistor

Example

If Ib=30µA and β=99, then the answer to the equation is:

Ie of transistor example

3rd Way to Calculate Emitter Current Ie


Using Known Values
If Ic and β are known, then Ie can be calculated by the formula:

How to calculate emitter current Ie from beta and collector current Ic

Example

If Ic= 2.97ma and β=99, then Ie is calculated out to be:

Example of calculating emitter current Ie from beta and collector current Ic

4th Way to Calculate Emitter Current Ie


Using Known Values
If Ib and Ic are known, Ie can be calculated using the formula:

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

Example
If Ic=3.95mA and Ib=50µA, then Ie calculates out to be:

emitter current example using base current and collector current Ic



Related Resources

How to Calculate the Base Current IB of a BJT Transistor

How to Calculate the Collector Current IC 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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