Question about Walter Brattain’s field-effect transistor principle.

In summary: This is a difficult question to answer in a paragraph. Transistors are used in a variety of ways, including as switches, amplifiers, and transmitters.
  • #1
Cyrus80772
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0
Question about Walter Brattain’s “field-effect transistor principle”.

The Wikipedia says “On 17 November 1947 John Bardeen and Walter Brattain observed that when electrical contacts were applied to a crystal of germanium the output power was larger than the input.“

Can someone please elaborate on how electrical contacts can be applied to a germanium crystal to make a power output larger than the input?

I don't see how you can get the current or the field to intensify just by putting a crystal inside a circuit.
 
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  • #2


A transistor (effectively a switch or an amplifier) is very closely related to a pair of diodes (effectively one-way valves).

The simplest way to see this is to look up vacuum tube valves and then triodes.

Rather than using vacuum tubes, another way to produce these devices is by joining two types of crystal (see n and p semiconductors). A less intuitive way to get the same result is by using surface effects on a single crystal (see "point contact" or "cat's whisker" diodes and triodes).

Note here that a crystal amplifier works the same as a car stereo amplifier: the amplifier does not produce power (it just controls the flow of an applied power source, like a switch). But the technology is pretty cute: you can build a "foxhole radio" with nothing more than a rusty razor blade, a length of wire with a pointy end, and an earphone.

..as for the FET, wasn't that Shockley?
 
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  • #3


How much semiconductor physics have you had? How about e/m field theory, circuit theory? You ask a broad question. It is hard to answer in a paragraph. The FET you refer to is explained all over the web. Search using the words "field effect transistor operation holes electrons". Also, you may include "majority carrier inversion insulated gate".

Are you reasonably familiar with diode theory of operation, i.e. electrons and holes? If not, I'd begin with that, and then work into transistors, FET or bjt. BR.

Claude
 
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  • #4


If I remember correctly the material Lilienfeld used for his mesfet wasn't germanium nor silicon but cadmium sulfide. With it he was able to make an amplifier that inverted the input signal but unfortunately the gain was always less than 1.
 
  • #5


skeptic2 said:
Lilienfeld [..] was able to make an amplifier that inverted the input signal but unfortunately the gain was always less than 1.
Seems like a typical use of the patent system: condemn everyone [else] to only using vacuum tubes for the next two decades ("for the good of society and progress").
 
  • #6


Thanks for the response,

I understand that when you use a crystal amplifier that it just modulates the output of the power supply. I just don’t understand what they ment when they said…

“John Bardeen and Walter Brattain observed that when electrical contacts were applied to a crystal of germanium the output power was larger than the input.”

How can you have more output power than input power? That sounds like “overunity”. I guess this was just a typo?
 
  • #7


A transistor has three contacts. One provides constant access to a large amount of power input. The next inputs a small amount of power in the form of a signal. The third is the signal output. By definition, the output signal must have more power than the input signal, or it wouldn't be an amplifier. There is no typo and no overunity, you're just forgetting about one of the three contacts.
 
  • #8


Cyrus80772 said:
How can you have more output power than input power? That sounds like “overunity”. I guess this was just a typo?
Stating cesiumfrog's comment another way, you are also supplying a DC bias in addition to the AC signal. The AC output power is less than the sum of AC + DC input powers.
 
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  • #9


in which field transistor is used widely
 

Related to Question about Walter Brattain’s field-effect transistor principle.

What is Walter Brattain's field-effect transistor principle?

Walter Brattain's field-effect transistor principle is a concept in electronics that describes the behavior of a semiconductor device known as a field-effect transistor (FET). It explains how the FET uses an electric field to control the flow of current through a channel in the transistor.

Who is Walter Brattain?

Walter Brattain was an American physicist who, along with John Bardeen and William Shockley, invented the first point-contact transistor in 1947. This invention revolutionized the field of electronics and laid the foundation for modern devices such as computers, cell phones, and other electronic devices.

What is the significance of Walter Brattain's work on field-effect transistors?

Walter Brattain's work on field-effect transistors was significant because it led to the development of the modern transistor, which is a key component in electronic devices. His research and experimentation helped pave the way for the advancement of technology and have had a profound impact on our daily lives.

How does the field-effect transistor principle work?

The field-effect transistor principle works by using an electric field to control the flow of current in a semiconductor channel. This channel is located between two regions, called the source and the drain, and is controlled by a third region called the gate. By varying the voltage on the gate, the electric field can either allow or block the flow of current through the channel, thus creating a switch-like behavior.

What are some practical applications of Walter Brattain's field-effect transistor principle?

The field-effect transistor principle has numerous practical applications, including in electronic devices such as computers, cell phones, and televisions. It is also used in amplifiers, oscillators, and other electronic circuits. Additionally, this principle is essential in the development of advanced technologies such as microchips, sensors, and solar cells.

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