BJT FIxed Bias

  • BIAS
  • BJT
comments powered by Disqus


The circuit referred here is called the fixed-bias circuit and is one of the simplest possible transistor-biasing circuits. The biasing components include two resistors, base resistor (Rb), collector resistor (Rc) and a supply voltage (Vdc0). The base-emitter junction gets forward-biased through Vdc and Rb. The supply voltage also reverse biases the collector-base junction through resistor Rc. Resistor Rb is of the order of few hundreds of kilo-ohms whereas Rc is of few kilo-ohms. The expression for the Ib can be derived to be:
Ib = (Vcc – Vbe)/Rb
We know Ic =  ß.Ib
Ic= ß[(Vcc-Vbe)/Rb]
Also from Kirchoff’s Law,
Vce = Vcc – IcRc
Fixed-bias circuit is the simplest possible biasing circuit requiring a very few components. However, the circuit offers worst stability against variations in temperature or transistor gain (ß) as compared to the other configurations. It is therefore prone to thermal runaway and is very rarely used.

Circuit info


Created on: 06 Nov 2013
<a href="" > BJT FIxed Bias <a/>