What are Basic Differences Between BJTs and FETs?

in STEMGeeks5 months ago (edited)

We know, transistors such as BJTs and MOSFETs are often used widely in electronics industries. Today, I'll discuss the fundamentals of transistors, BJTs, and FETs, as well as their differences.

Transistors are available in a wide range of forms and sizes. Unipolar and bipolar transistors are both types of transistors. Additionally, bipolar transistors are classified into two types. They are also referred to as NPN and PNP. These are the most frequently used transistors. A semiconductor element is a circuit made up of a material element that provides gain or switching by raising the electrical input voltage and current signal to the output voltage and current signal.

BJT (Bipolar Junction Transistor)

In electronic circuitry, a bipolar junction transistor (BJT) is a three-terminal semiconductor device with two p-n junctions that can be used to increase or decrease the volume of a signal. It is a device that is controlled by a flow of electricity. The three terminals of a bipolar junction transistor are the base, collector, and emitter.
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When a signal with a small amplitude is applied to the transistor's base, it is amplified and made available at the collector. In this particular instance, the BJT offers amplification. There are two types of bipolar junction transistors: PNP bipolar junction transistor and NPN bipolar junction transistor
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Symbol for NPN bipolar transistor with current flow direction

FET (Field-Effect Transistor)

The term "field effect transistor" refers to these transistors. The sentence is constructed from the first characters of the FET English word Field-effect T ransist. Transistors, or active circuit elements, exist in a range of shapes and sizes. MOSFETs, a form of FET, are the most widely used transistor type today, alongside BJTs.
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MOSFET Structure


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n-junction field-effect transistor

BJTs and FETs were used as transistors. Despite the fact that their working logic is similar, they have some structural differences. The following distinctions are made:

  • BJTs require an input current to trigger. FETs, on the other hand, do not require any input current.

  • The curve connecting the input and output of the BJT is linear. Small signals are linear in FETs, whereas large signals are non-linear. As a result, when significant signals are present, the FETs degrade.

  • FETs are rapid. As a result, FETs switch faster than BJTs.

  • Unlike BJTs, FETs' gate circuits do not require resistors. Additionally, this simplifies our circuit.

  • FETs outperform resistors as a switching element. Because the majority of FETs have a very low switching resistance, often between 1 and 10 ohms. This suggests that they are more likely to switch effectively.

  • Unlike BJTs, which convert current to current, FETs convert voltage to current.

  • FETs turn on when the Gate-Source voltage exceeds the threshold voltage. The Gate voltage in FETs can be anywhere between the Source and Threshold values, whereas the Base-Emitter voltage in BJTs is consistently close to 0.7 V regardless of the input current.


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Sir, why my post is not showing inside picture?