Enter the base bias voltage (volts), the base-emitter volt drop (volts), and the base input resistor (ohms) into the calculator to determine the Transistor Base Current. 

Transistor Base Current Formula

The following formula is used to calculate the Transistor Base Current.

Ib = ( Vb - Vbe) / Rb
  • Where Ib is the Transistor Base Current (amps)
  • Vb is the base bias voltage (volts) 
  • Vbe is the base-emitter volt drop (volts) 
  • Rb is the base input resistor (ohms) 

To calculate the transistor base current, subtract the base-emitter volt drop from the base bias voltage, then divide by the base input resistor.

How to Calculate Transistor Base Current?

The following example problems outline how to calculate Transistor Base Current.

Example Problem #1

  1. First, determine the base bias voltage (volts). In this example, the base bias voltage (volts) is determined to be 18 .
  2. Next, determine the base-emitter volt drop (volts). For this problem, the base-emitter volt drop (volts) is measured to be 17 .
  3. Next, determine the base input resistor (ohms). In this case, the base input resistor (ohms) is found to be 9.
  4. Finally, calculate the Transistor Base Current using the formula above: 

Ib = ( Vb – Vbe) / Rb

Inserting the values from above and solving yields: 

Ib = ( 18 – 17) / 9 = .11 (amps)

Example Problem #2

Using the same method as above, determine the variables required by the formula. For this example problem, these are:

base bias voltage (volts) = 8

base-emitter volt drop (volts) = 7

base input resistor (ohms) = 3

Enter these given values into the calculator or above yields: 

Ib = ( 8 – 7) / 3 = .333 (amps)