Understanding PNP and NPN Transistors

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Homework Help Overview

The discussion revolves around understanding the current flow in PNP and NPN transistors, focusing on the differences in their operation and current paths. The original poster expresses difficulty in determining the current path in an NPN transistor after analyzing a PNP transistor circuit.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to understand the current flow in an NPN transistor, questioning the starting point of the current. Some participants suggest that the circuits are symmetric and that the current directions are simply reversed between the two types of transistors.

Discussion Status

The discussion is ongoing, with participants providing insights into the similarities and differences between the two transistor types. Some guidance has been offered regarding the symmetry of the circuits, but the original poster's specific confusion about the NPN current path remains unaddressed.

Contextual Notes

The original poster is working within the constraints of a homework assignment, which may limit the depth of exploration into the topic. There is an implicit assumption that both transistor types operate under similar principles, which is being questioned.

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Homework Statement



revered members,
in the following attachment, i could work out the path of current in pnp transistor, that is, from base through RB AND THE output is taken across RL.
but i can't figure out the path of current in npn transistor. could u please help?

Homework Equations





The Attempt at a Solution


 

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Why are you having difficulty? The two circuits are completely symmetric. Just replace I in the PNP circuit with -I in the NPN circuit. The currents will be the same, just in the opposite direction.
 
in pnp circuit, current flows from emitter to base and it reaches the collector. but in npn circuit current flows from base to emitter and to ground. where is the starting point for current in npn circuit. that is the problem for me
 
Both transistors work exactly the same. In both, charge carriers are emitted by the emitter, pass through the base (where a few recombine), and are collected by the collector. The only difference is that in the NPN device the charge carriers (electrons) have a negative charge. So while in the PNP device, most of the current flows from the emitter to the collector, with a small amount going out the base, in the NPN device, current flows from the collector to the emitter, with a small amount coming in from the base.
 

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