Friday, March 20, 2009

Transistors n such


So since I had to learn how transistors work and what they actually are, i thought id write about them. Transistors are cool - apparently most everything electronic you have ever had anything to do with (post invention of the transistor) had one or more transistors in it. Quick disclaimer: what im about to write about may be horribly inaccurate and possibly wrong, but is what i understand about transistors.

Soooo transistors have 3 legs on them, called Base, Collector and Emitter and they work like this. If you give some current to the Collector leg then nothing much happens. If you give current to the Base leg only, then i think that you will see it pop out the emitter (provided of course that it is connected to ground or whatever). Now heres the fun part: Give some current to Collector AND to the base, then you get base + collector coming out of the emitter. So pretty much its like a switch between Collector and emitter that you can turn on or off (or steppings thereof) by supplying some (much lower) current to the base leg.

Say for example you have a basic stamp or something that only supplys 10ma (i made that number up but what it supplys is low enough) but you need 100ma to run all your led's and whatnot. Easy, just point the 10ma to the base of your tranny that has 100ma on its collector. Now its emitter has 110 coming out of it.

Now it gets a touch more complex than this as there are various different transistors out there that can handle different max voltages/currents and need different amounts of voltages/current on their base to turn them on or off. I use a 182b transistor for my stuff as it is a general multipurpose tranny that (luckily) does what i need it to do.

Oh heres a fun fact. If a tranny is completely off or completely on, then it generates not very much heat. If it is partially on, then it will generate heaps of heat as it is actively curbing the amount of stuff (current/voltage/whatever) going thru it, and the stuff that isnt getting through is being disappated as heat. This is why (i assume) some trannys are attached to heatsinks.

Something else to be aware of is that trannys can come in different packages and the pinouts may change. Read the datasheet on your trannys to work out which pins are B, C and E. Additionally there are 2 types of transistors: NPN and PNP. I just described an NPN transistor.

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