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What are NPN and PNP diodes How do they work ?

NPN (Negative-Positive-Negative) and PNP (Positive-Negative-Positive) are transistor configurations, not diodes. However, I assume you meant NPN and PNP transistors, which are commonly used in electronic circuits. Let’s delve into the working principles of NPN and PNP transistors:

NPN Transistor:

An NPN transistor consists of three semiconductor layers: a thin P-type (positive) layer sandwiched between two N-type (negative) layers. The three layers form two P-N junctions. The terminal connections are referred to as the collector (C), base (B), and emitter (E).

  1. Biasing: When a voltage is applied across the collector and emitter (V_CE), the transistor is said to be forward-biased. Additionally, a small voltage is applied to the base with respect to the emitter (V_BE). This biasing arrangement allows current to flow from the collector to the emitter.
  2. Operation: In an NPN transistor, the majority carriers are electrons. With forward biasing, electrons from the N-type emitter region move towards the P-type base region. Some of these electrons cross the thin base region and reach the N-type collector. The flow of electrons from the emitter to the collector constitutes the collector current (I_C).
  3. Amplification: The current flowing through the collector-emitter path is controlled by the small current flowing into the base-emitter path. This property enables NPN transistors to act as amplifiers, as a small signal at the base can control a larger signal at the collector.

PNP Transistor:

A PNP transistor has a structure opposite to that of an NPN transistor. It consists of three layers: two P-type layers with an N-type layer sandwiched between them. The terminal connections are the collector (C), base (B), and emitter (E).

  1. Biasing: Similar to the NPN transistor, when a voltage is applied across the collector and emitter (V_CE), the transistor is forward-biased. A small voltage is applied to the base with respect to the emitter (V_BE).
  2. Operation: In a PNP transistor, the majority carriers are holes. With forward biasing, holes from the P-type emitter region move towards the N-type base region. Some of these holes cross the thin base region and reach the P-type collector. The flow of holes from the emitter to the collector constitutes the collector current (I_C).
  3. Amplification: Just like in NPN transistors, PNP transistors can amplify signals. The small current flowing into the base-emitter path controls a larger current flowing through the collector-emitter path.

Summary:

Both NPN and PNP transistors operate as current-controlled devices, where a small input current at the base controls a larger output current between the collector and emitter. These transistors are fundamental building blocks in electronic circuits, serving various functions, including signal amplification, switching, and voltage regulation.

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