Understanding PNP and NPN Transistors

[logearav]

Homework Statement

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

Homework Equations

The Attempt at a Solution

 

[phyzguy]

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.

 

[logearav]

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

 

[phyzguy]

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.

 

[paranormal]

Hello,

Thank you for your question. Understanding the path of current in PNP and NPN transistors is a fundamental concept in electronics and it is important to have a clear understanding of it.

In a PNP transistor, the current flows from the emitter to the collector, with the base acting as a control terminal. This means that the current is controlled by the amount of current flowing into the base terminal. The base-emitter junction is forward biased, allowing current to flow through it. The collector-emitter junction is reverse biased, which allows the current to flow from the emitter to the collector.

In an NPN transistor, the current flows from the collector to the emitter, with the base still acting as a control terminal. However, the direction of current flow is reversed compared to a PNP transistor. The base-emitter junction is still forward biased, but the collector-emitter junction is now forward biased as well. This means that the current flows from the collector, through the base, and out through the emitter.

To better understand the path of current in an NPN transistor, it is helpful to think of it as two back-to-back diodes. The base-emitter junction acts as a forward biased diode, allowing current to flow from the base to the emitter. The collector-emitter junction acts as a reverse biased diode, allowing current to flow from the collector to the base. This current then flows through the base-emitter junction and out through the emitter.

I hope this helps to clarify the path of current in PNP and NPN transistors. If you have any further questions, please don't hesitate to ask. Happy studying!