How do resistor values affect the operation of a BJT transistor?

[ajack]

I'm really confused between saturation and amplifier. When will the transistor work in saturation mode and in amplifying mode? Resistors are the matters. We chose the resistors so that the transistor will work in saturation or amplifying. How can we chose?

 

[ranger]

We chose the resistors so that the transistor will work in saturation or amplifying. How can we chose?

Well you choose the resistor values depending on how you want the transistor to operate. As an example you may want to choose the q points so that the transistor is mid-point biased. These Q point values are determined by the (biasing) resistors used. The process of setting the proper operating(Q) point for a transistor/amplifier is called DC biasing. There are several biasing techniques, each with its own advantages and disadvantages. Here are a few links
http://www2.engr.tu.ac.th/~lvenus/classes/le210/biasing.pdf
http://www.allaboutcircuits.com/vol_3/chpt_4/8.html

 

[ravenprp]

A saturated BJT (bipolar junction transistor) refers to a state where the transistor is fully conducting and there is no further increase in the collector current, even with an increase in the base current. This can be thought of as the “on” state of the transistor. On the other hand, an amplifier refers to a circuit that increases the amplitude of an input signal, and in the context of transistors, this usually means increasing the voltage or current of the signal.

The confusion between saturation and amplification may arise because both terms involve the behavior of the transistor, but in different ways. A transistor can work in both saturation mode and amplifying mode depending on the circuit configuration and the input signal. In saturation mode, the transistor is acting as a switch, allowing current to flow from the collector to the emitter without any significant amplification. In amplifying mode, the transistor is acting as an amplifier, where a small input signal is amplified to a larger output signal.

The choice of resistors in a circuit can affect the operation of the transistor and determine whether it will work in saturation or amplifying mode. The values of the resistors can be selected to control the biasing of the transistor, which is the process of setting the operating point of the transistor. This is important because the operating point determines whether the transistor will be in saturation or amplifying mode. By carefully choosing the values of the resistors, we can ensure that the transistor operates in the desired mode.

In summary, a saturated BJT and an amplifier are two different modes of operation for a transistor. The choice of resistors in a circuit can determine the mode of operation of the transistor, and this can be controlled by carefully selecting the values of the resistors. It is important to understand the differences between saturation and amplification in order to design and optimize transistor circuits for specific applications.