Transistor in saturation region

In summary, the conversation discusses the behavior of an NPN transistor in the saturated region and the implications for base current. It also addresses a potential contradiction in the common emitter configuration. The conversation suggests considering the effects of biasing and collector resistance in understanding the behavior of the transistor. The idea of a designer understanding the inner workings of devices is also brought up.
  • #1
erece
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when transistor is operated in SATURATED REGION , then for npn transistor BC junction becomes forward biased and holes will move from base to the collector, so more holes should be provided by the battery to the base terminal.
So if this is the case then base current should increase . But when we analyse the common emitter configuration then on applying KVL to input loop we get base current same in both active region and saturation region. How this is contradicting my previous conclusion of " increase in base current"
 
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  • #2
I have to admit I didn't really follow the logic but maybe this will help:

You have to also consider what lowered Vc to saturate the NPN. For the standard NPN common emitter what you should find is if the biasing network is holding Ib constant then Ic will have to drop, i.e. the collector resistor gets larger, to saturate the NPN. So for this particular application, although Ib stays constant, Ic/Ib drops.
 
  • #3
erece said:
when transistor is operated in SATURATED REGION , then for npn transistor BC junction becomes forward biased and holes will move from base to the collector, so more holes should be provided by the battery to the base terminal.
So if this is the case then base current should increase . But when we analyse the common emitter configuration then on applying KVL to input loop we get base current same in both active region and saturation region. How this is contradicting my previous conclusion of " increase in base current"
Does this thread help? https://www.physicsforums.com/showthread.php?t=636127
 
  • #4
is it not necessary for a good designer to look inside working of devices ??
 
  • #5


In the saturated region, the transistor is being operated at its maximum current-carrying capacity. This means that the base-emitter junction is forward biased and the base-collector junction is reverse biased. In this state, the transistor is fully turned on and acts like a closed switch, allowing a large amount of current to flow from the collector to the emitter.

In the common emitter configuration, the base current is controlled by the input voltage and the base-emitter junction characteristics. As the input voltage increases, the base-emitter junction becomes more forward biased and allows more current to flow through the base. However, in the saturated region, the base-emitter junction is already fully forward biased and cannot allow any more current to flow. This is why the base current remains the same in both active and saturated regions.

The increase in base current that you observed may be due to other factors such as changes in the input voltage or variations in the transistor's characteristics. It is important to consider these factors when analyzing the behavior of a transistor in different regions.
 

1. What is the saturation region of a transistor?

The saturation region of a transistor is a state in which the transistor is fully conducting, with the collector current being at its maximum value and the collector-emitter voltage being at its minimum value.

2. How does a transistor enter the saturation region?

A transistor enters the saturation region when the base-emitter junction is forward-biased and the base-collector junction is reverse-biased. This allows a large amount of current to flow from the collector to the emitter, resulting in saturation.

3. What is the significance of the saturation region in transistor operation?

The saturation region is important because it allows the transistor to act as a switch, with the ability to control the flow of current between the collector and emitter. In this region, the transistor is fully on and can pass a large amount of current with minimal voltage drop.

4. How does the saturation region affect the voltage and current characteristics of a transistor?

In the saturation region, the collector-emitter voltage remains relatively constant while the collector current increases with an increase in base current. This results in a horizontal line on the voltage-current graph, indicating that the transistor is fully conducting.

5. How can the saturation region of a transistor be controlled?

The saturation region can be controlled by adjusting the base current. A higher base current will result in a larger collector current and a lower collector-emitter voltage, while a lower base current will decrease the collector current and increase the collector-emitter voltage.

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