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Hi.
I've just rear this article http://www.interq.or.jp/japan/se-inoue/e_car1_3.htm wich describes how transistor ON - OFF state (saturnation state ???) works. However. It still left me confused (sure I learned something but... ;D). I still can't figure out that hfe, resistor, capacitor, base and collector current, and 0.6V calculations. Majbe it's becouse his bad english (look who's saying ;) ) at certain parts of article or I'm just not seeing sometnihg. Anyway, does anyone know of different article (or can explain me differently how this works) that could help me understand this better? Since I wan't to build car starting system based on transistors (I have the schematics and just want to know how whole thing works) any help before blowing my self to pieces is appriciated :)
Cheers

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Hello EDY!

You are right, the english writing of a japanise people reflects the japanese complexity !!

hFE is a number which accompany each BJT transistor (may differ from transistor to transistor). It's a number that tells you how many times the base current will be multiplied and finally ampified. The amplified current it's the current that flows from C (collector). You need to know this if you are using the transistor for amplification. If you use it just for a on-off state you don't care much about it.

You must believe (like a principle) that the BE voltage when transistor conducts is 0,6V. It's like the constant voltage of a common diode right polarized. Also a voltage of about 0,2V exists at CE when the transistor conducts.

Having this things in mind (also the 12V at IN) you can easily calculate the resistor current. The base current must be enough to take the transistor in full conduct. It is controlled by R1. So R1 must have such a value to make the transistor condust. If the base current is small then the C current is proportional to this small current. If the base current exceed a value (it depends on the transistor) then the C current depends on the internal resistance of the relay because it like closing a switch between Collector and Emitter.

I wish i helped to clarify the transistor characteristics, but keep in mind that it's not so easy to understund the BJT transistor in one day. Everyday you will detect a new characteristic until you finally undestand it completely.

Tell me if something went wrong.

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Tanx Mike!
I think I'm begining to understand the whole concept of transistors. And like you said it every day I'm figuring something out. Hope I'm close to completing process of "figuring it out" ;) As far as my transistor starter project I'm still looking to find a suitable high voltage npn transistor. Local stors don't have any so I'm using different chanels to find it. If everything goes well, and I don't blow my self to sky, I'll post the schematics and pcb.
Cheers

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• 1 month later...

Here is BJT Transistor Review I found:

http://www.electronics-lab.com/articles/files/BJT_Transistor_Review.doc

More electronics articles here: http://www.electronics-lab.com/articles/index.html

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• 2 weeks later...

Tanx mike :)

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• 2 weeks later...

:)hi EDY

am i correct to assume that you are trying to build an electronic ignition system, well here's a few that you can consider;

1. MJ10008 npn 175w 450v 20A (darlington) TO-204
2. MJ10023 npn 250w 400v 40A (same) TO-3
3. MJ10015 npn 250w 400v 50A (same) TO-3 :)

these are motorola products.

hope this can help

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• 2 weeks later...

tanx mozikluv
I havent noticed before your post
I all ready have the schematics for it and just wanted to figure out how it works.
but those transistors you mentioned could come in handy for future upgrades
cheers

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