Basic Functionality of a PNP Transistor
The basic connection of a PNP transistor is shown in the following figure.
Let us see those Transistor working principle Effect on emitter-base connection. This is forward facing and if the collector is floating to the left , most of the carriers (holes) from the emitter diffuse to the base, and most of the carriers (electrons) from the base diffuse to the emitter.
Now, if the base collector is reverse biased and the emitter remains floating, the width of the depletion layer at the collector-base junction increases; therefore, there is no flow of majority shareholders. However, there is current flow due to thermally generated minority carriers.
Let us now consider the operation of a PNP transistor whose base-emitter junction is forward biased and its base-collector junction is reverse biased. Many majority carriers (holes, say X in the emitter and electrons, Y in the base) diffuse through the forward biased p-n junction.
Therefore, the total current flowing through this connection is the sum of the hole diffusion current and the electron diffusion current. This total current is called the emitter current and is denoted by I. E ,
Emitter current I E = I P (x) + I N (J)
Since the central area, i.e. the base, is very thin and lightly doped, most of the charge carriers emanating from the emitter have little chance of recombining at the base and reaching the collector through the base area. Only a few majority charge carriers (x) are lost through recombination. In practice, about 2% of the majority charge carriers diffuse into the base and recombine with electrons.
The total loss of number of electrons (Y+y) is the flow of an equal number of electrons from the negative terminal of a DC V EE battery into the base. The base through such electrons forms the base current I b Therefore, the magnitude of the base current IB is very small and is on the order of microamperes.
If X(=y) is the number of holes that combine with electrons, then the loss of the total number of holes in the emitter is (X+x). This loss involves the flow of an equal number of electrons from the emitter to the positive terminal of the DC V EE battery. These electrons go from the emitter to the positive terminal of the DC V EE battery. These electrons are released from the covalent bonds of the crystal atoms in the emitter and an equal number of holes are created.
The potential V CCC in the right section is such that carriers arriving at this section are slightly attracted when current begins to flow. This current is called collector current Ic and is almost equal to the emitter current.
The collector current also has a second current component. This current is due to minority carriers called reverse saturation current; The ICBO flows through a reverse-biased collector diode. Therefore, the collector current IC is the sum of the leakage current I CBO, and remaining emitter current (=I E(Xy) )
= L C(Xy) + L CBO
The more carriers from the emitter to the collector, the greater the device's power gain. The base must be very thin and the base-collector interface large. The collector current is therefore only slightly higher than the emitter current.
If we apply Kirchhoff's current law to the transistor, we obtain
Basic Functionality of NPN Transistor
The figure above shows the NPN transistor with forward bias at the base-emitter connection and reverse bias at the base-collector connection. The forward bias voltage V EE causes the majority carriers (electrons) in the n-type emitter to diffuse to the base and the holes to diffuse from the base to the emitter.
The flow of majority charges forms the emitter current. As these electrons flow through the p-type base, they tend to combine with holes. Because the base is lightly doped and thin, only a few electrons combine with holes. As the base is lightly doped and thin, only a few electrons combine with holes and form the base current I b.
The remaining electrons enter the collector region and form the current I C. This collector current is also called injected current because it is generated by electrons injected from the emitting region.
The emitter current is the sum of the collector current and the base current.
Points to remember
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The emitter current of a transistor consists of two components: base current and collector current.
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The base current is a small fraction of the emitter current, about 2% of the emitter current, and the collector current is about 98%.
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The collector current arises mainly from injected electrons (majority carriers) from the emitter. The collector current also has a second component due to thermally generated minority carriers, called reverse saturation current.
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The emitter-base connection is always forward biased and the collector-base connection is always reverse biased.
Conclusion
In short, the way PNP and NPN transistors work is at the heart of electronic circuits. These devices allow us to control and amplify electrical signals, making them essential in modern technology. Whether amplifying audio signals in your headphones or processing data on your computer, transistors are the unsung heroes of the digital age. Understanding the principles outlined in this article will help you better understand the magic that happens inside your electronic devices.
Common questions
What is the main difference between PNP and NPN transistors?
The main difference is in the semiconductor materials they are made from. PNP transistors use P-type material for the emitter and collector, while NPN transistors use N-type material for these areas.
Why is the base current in transistors so low?
The base current is intentionally kept small to ensure that most of the majority carriers (electrons or holes) flow from the emitter to the collector, allowing amplification. Only a small part of these carriers form the base current.
What causes collector current in a transistor?
The collector current consists mainly of electrons injected from the emitter, most of which are carriers. In addition, there is a smaller component, the so-called blocking saturation current, which results from thermally generated minority carriers in the collector-base connection.
