Understanding Transistors: How Base Current Controls Collector Current

  • Thread starter jd12345
  • Start date
  • Tags
    Transistor
In summary: Objects/ViewObject.aspx?ID=DIGIT401In summary, transistors work by controlling the flow of current through a semiconductor material. The base current in a common emitter transistor can control the larger collector current, either directly or through a process called "beta-dependent" control. Beta, the ratio of collector current to base current, varies and can affect performance, while alpha, the ratio of collector current to emitter current, is more consistent and predictable. The most common application for controlling the base current is in saturated switches. It is recommended to refer to university textbooks and OEM websites for accurate information on transistors rather than relying on amateur hobbyists on the internet. Interactive resources, such as the
  • #1
jd12345
256
2
I'm trying to understand working of transistor( common emmiter ) and there is one line that i don't understand and i ahve found that line in many books :- " A small change in base current controls the larger collector current" . I don't understand how the base current controls the collector current.
Can someone explain. Also if someone has a link explaining transistors it would be helpful
 
Engineering news on Phys.org
  • #2
We typically control the collector current by controlling the emitter current value. Then Ic = alpha*Ie. If we control base current Ib, we get a collector current given by Ic = beta*Ib. This type of method is called "beta-dependent", and is usually avoided. Alpha is very consistent and predictable over speciman, current value, and temperature, having values from 0.98 to 0.998. Hence if we take the value of alpha at 0.99, we are at most off by 1%.'

Beta, OTOH, can be as low as 50 & as high as 500. It varies with temperature, current value, and speciman. The most common application where base current is the contrrolled input is saturated switch. By overdriving the base, we force the collector to saturate. If minimum beta is 50 worst case, but we force base current to be 1/10th of the collector current, the device saturates reliably.

Devices with beta of 50, 100, 200, & 400, all saturate with near identical performance. For most applications, we design a network so that Ie is a specific value, then we know that Ic = alpha*Ie. That is how we control the bjt.

I would recommend university textbooks on electronics and peer-reviewed publications. Under no circumstances do I advise "web surfing". The web is filled with amateur electronics hobbyists who seem to have an insatiable urge to lecture on electronics as if they were a professor. OEM web sites like On Semi, Fairchild, etc. are also a good source of info. Avoid self-proclaimed "experts". Anybody who claims that the uiversities and OEMs got it wrong should be ignored.

I hope I've helped.

Claude
 
  • #3
ok thanx
 
  • #4
jd12345 said:
... Also if someone has a link explaining transistors it would be helpful

cabraham said:
... The web is filled with amateur electronics hobbyists who seem to have an insatiable urge to lecture on electronics as if they were a professor.

I concur about the web having lots of trash, but this site is good.

Transistors
Transistor Operation

With interactive images such as this:

tran10.gif
 
  • #5


Transistors are a fundamental component in modern electronics and understanding their operation is crucial for any scientist. In the common emitter configuration, the base current controls the larger collector current through a process called amplification.

To understand this, we need to first understand the structure of a transistor. A transistor is made up of three layers of semiconductor material - the emitter, base, and collector. The base layer is very thin, and it acts as a control element for the flow of current between the emitter and collector.

When a small current is applied to the base, it creates an electric field that allows a larger current to flow from the emitter to the collector. This is known as the amplification process. The amount of amplification is determined by the properties of the transistor, such as its size and material composition.

In other words, the base current acts as a switch that controls the flow of a larger current between the emitter and collector. This is why it is often said that a small change in base current can lead to a larger change in collector current.

To better understand the mechanics of transistors, I recommend checking out some online resources that explain the concept in more detail. Some good starting points could be websites such as Electronics Tutorials or SparkFun, which offer step-by-step explanations and visual aids to help you understand the inner workings of transistors. Additionally, you can also refer to textbooks or attend workshops or seminars on transistors to gain a deeper understanding of their operation.
 

FAQ: Understanding Transistors: How Base Current Controls Collector Current

What is a transistor?

A transistor is a semiconductor device that is used to amplify or switch electronic signals. It consists of three regions of doped material, known as the emitter, base, and collector, and can be either NPN or PNP type.

How does a transistor work?

A transistor works by controlling the flow of current between two of its regions (collector and emitter) by varying the voltage applied to the third region (base). When a small current is applied to the base, it allows a larger current to flow between the collector and emitter, effectively amplifying the signal.

What is the relationship between base current and collector current in a transistor?

The relationship between base current and collector current is described by the current gain, also known as the beta (β) value. This value represents the amplification factor of the transistor and is typically in the range of 50-300 for most transistors. It can be calculated by dividing the collector current by the base current.

How does base current control collector current in a transistor?

The base current controls the collector current in a transistor by modulating the width of the depletion region between the base and collector regions. When the base current is increased, it decreases the width of the depletion region, allowing more electrons to flow from the emitter to the collector, resulting in a larger collector current.

What are some common applications of transistors?

Transistors are used in a wide range of electronic devices, including computers, radios, televisions, and smartphones. They are also used in power amplifiers, switching circuits, and voltage regulators. Additionally, transistors are used in integrated circuits (ICs) to create complex electronic systems.

Back
Top