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Topic: How does a transistor work? (Read 677 times) previous topic - next topic

Drew Davis

I'm going to control a motor according to the link below but I want to know why it works like that. I Understand why you need the base and the emitter but what function does the collector serve? Also what purpose does the capacitor serve?



James C4S

I Understand why you need the base and the emitter but what function does the collector serve?

The current allowed to flow from Collector to Emitter is proportional to the current flowing from base to emitter.  It's the basis of how a (NPN) transistor works.  https://www.google.com/search?q=how+does+a+transistor+work

Also what purpose does the capacitor serve?

Filtering the noise from the motor.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com


A silicon transistor uses impurities like phosphorus and arsenic to produce diodes at two juctions. The base-emitter junction has a doped base and a heavily doped emitter so that the diode currents there have small numbers of charge carriers from the base and large number of charge carriers from the emitter crossing the junction. The amplification is because of that. A small base current produces a larger emitter current because that diode has holes and electrons flowing in unequal amounts. The collector is close to that diode, so diffusion lets that large emitter current go into the collector while the base has a small current. The collector is lightly doped so the diffusion of charge carriers proceeds from a volume with many carriers to a collector with few carriers.
I am going to get going.

Drew Davis

Thank you for all the explanations. I have learned so much from the Arduino Forum!


Jun 28, 2013, 05:16 am Last Edit: Jun 28, 2013, 05:40 am by pwillard Reason: 1
Gee... Why do people always want to place the inductive kick back diode in the wrong place.

Maybe it's not obvious on a physical layout (IE; Fritzing), but when you draw it as a schematic, something looks wrong.

(I'm not a fan of instructables... I pretty much only ever see bad advice... like "you don't need resistors on your LED's" and such.  This is just another example of someone almost understanding... but then *not* really...)

I put an example diode (D2) in the circuit to show where it *should* go.

Lets see shall we?

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