technology of transistors

[Toney]

HI to all,
This site has really got me fired and I'm glad I found it.
So ,..I am still on an absorb as much information as possible type learning curve. Reading as much as I can find , but I got a little stuck on transistors. I know it sounds der-obvious and they are as common as anything , but I would really like to understand them rather than just use them.
 I have googled myself all over the web and feel pretty ok with the explanations regarding FET types, but don't quite get it as to how bipolar transisters actually work. Particularly how they actually amplify a signal.
As a famous TV professor used to say here in OZ ,"why is it so?".
Does anyone have some pointers to a clear tutorial on the technology of transistors?    
Yes, I am a newbie.......

[niftydog]

well, I always put it like this; a small current on the base controls a much, much larger current through the collector-emitter. (obviously this applies to common emitter amps)

Kinda like a tiny, easy to turn tap on a really big high-pressure hose!

some links;
http://www.tpub.com/content/neets/14179/css/14179_61.htm
http://users.pandora.be/educypedia/electronics/composemiconductors.htm

Trouble is, there's layers of understanding that goes on here:

"I just match up the numbers and pins and hope it doesn't blow up" :shock:

"I know how to use them and I know how not to blow them up"  

"I know how they work and I can design any transistor circuit with confidence"

"I know what 'holes' are and can tell you more or less how a PNP junction works"   :|

Then there's

"I design transistors for a living, I started back in the days of point-contact construction, and I know more about them than most people would care to think about"  

So, you sorta have to decide how much you want to understand them!


Geez, I tell you what, we need a "tutorial links page" or something... I've given out tons of links in answer to common questions like this!

[Peter Snowberg]

A page of tutorials would be a GREAT thing!

There's so much good info out there and it can be hard to find. I would love to add a list of tutorials to the FAQ.

[bwanasonic]

There are still those old fashioned paper things called books !  :lol:  I just picked up "Basic Electronics" , a Reprint of the Bureau of Naval Personnel Training Manual *. It's a great book, and even features an extensive section on tubes. Check your local library.

Kinda like a tiny, easy to turn tap on a really big high-pressure hose!

This is exactly the model that popped into my head when reading the above mentioned book!

Still striving towards an intuitive mental model for a lot of electronics concepts myself.

Kerry M

* ISBN 0-7607-5239-7

[Phorhas]

Yeah, a turorial page would be a great thing to do!

[Toney]

Thanks NIFTY DOG,
I think your analogy makes good, clear sense.
Weird thing is, I had no worries understanding the constuction of the little fellas. Got the bit about doping and holes, as in adding Arsenic to the mix in construction, thus creating wanted imperfections in the stucture to act as conduits between the layers etc.
But, around 12:30 last night, having taken my faded memories of highschool chemistry as far as they would go, I realised I was learning things that were way beyond the application and I still hadn't answered my original question.
Had there been a Transistor in stomp box technology tutorial, that would have been excellente.
Totally get the switching bit, but straining brain to figure how the base signal is actually transformed into an amplified copy via the collector/emmiter.
(thank you beer for killing all those vital brain cells)

[Steben]

Actually, you can call a FET also a big hose with a tiny tap...
With most BJT's however, the hose is even bigger.
FET's are voltage controlled (input voltage controls drain current)
BJT's are curent controled (input current controls collector current)

FET stages are easier to design and build, but usually have less gain and are very difficult to match (very little FET's have the same bias and gain).
BJT's are most of the time complicated, have different ways of operating and biasing, but are less prone to characteristic variety.
I don't think it's really needed either to understand BJT's completely. the best Bipolar circuits for use in this "branche" are not that "engineered" after all...

[Toney]

Ok, so one part of the logic impasse is revealed! :idea:
Who'd a thought the arrow on a transistor emmiter symbol points in the oppposite direction of electron flow. Sheesh, thats helpfull (not) for people trying to get a grasp on schemetics !
Reading through Lessons in Electric circuits from Niftydogs' link. Really good stuff, some bits bit hard to "get" but lots of good stuff.  Getting there. Don't understand why the base current isn't overwhelmed by the much larger current at the c/e junction. Thinking I have read that electricity always takes the path of least resistance..... :?:  :!:

[niftydog]

Who'd a thought the arrow on a transistor emmiter symbol points in the oppposite direction of electron flow.

not many people talk "electron flow". Think "conventional current" and it makes more sence.

Don't understand why the base current isn't overwhelmed by the much larger current at the c/e junction

you need also to look at the theory of simple PN junctions (diodes, try that same www.tpub.com link, chapter 2 I think)

[toneman]

The *best* way 2 "learn" transistors is 2 *use* them in a project.
the "learning" comes about when the project *doesn't* work
and U have 2 troubleshoot it 2 get it flying.
"best" projects are kits with theory of operation.
Old Heathkits were what i learned on.
AND, of course, PAIA, still in business, 30years!!! and counting.
And introduction 2 trannys is good as longas U link it to practical,
handson experience with a powersupply, oscope and DMM.
just my 2watts worth
tone

[R.G.]

(a) see the last part of http://geofex.com/Article_Folders/How_It_Works/hiw.htm for some simple illustrations.

(b) here's the poop:
A bipolar transistor is a pair of junctions made together. It's a sandwich of (for instance) N-type, P-type, and N-type (again) silicon. For historical reasons, the middle is the "base" and the ends are the "emitter" and "collector" of moving charges. Those names are useful primarily as name tags these days.

If you put a voltage across the two N's and leave the P-base open, nothing happens. This is because a semiconductor junction conducts when the applied voltage is in the same direction as the doping type - positive to P-type and negative to N-type. If the voltage is reversed, no current flows. The reasons for no current flowing in the reverse direction are tucked down in semiconductor physics, but the simplest way is to think that the external reverse supply "eats" all of the available P-type carriers on the P-side, sucking them down into the negative side of the supply, and also all the n-type charge carriers on the N side, sucking them down into the positive side of the supply.

This causes a "depletion region" in the middle of the junction where there are no charge carriers left to let current flow.

Back at the transistor, no matter which way you hook up the N's, one of them is connected to the positive supply and so the junction between the most positive N-type stuff and the P-type base is reverse biased. No current can flow.

So we have two junctions stacked on top of each other. The positive power supply connects to one N-type region, the negative power supply to the other N-type region. The "top" junction is depleted, no current flows, and the bottom junction *would* conduct, except all current is already blocked by the depleted top junction.

... and then we trickle a little current into the base...

Making the P-type base a little positive lets current flow into the now-forward-biased PN base to emitter junction. This current is the same as would flow through any PN-diode under similar conditions. But at the same time, you're injecting charge carriers into that depleted upper diode junction region. With charge carriers now available, current flows through the reverse biased upper diode region. In effect, the base current lets the power supply force charge through an otherwise blocking diode. What makes this all interesting is that a little base current lets a much higher collector current flow - it's a little like removing the props from a suspended weight; a little sideways force on the prop lets a big weight fall. If you quit putting in base current, the collector junction gets re-depleted, and collector current quits flowing.

The amount of collector current that flows per amount of base current is called the current gain, hFE, HFE, lots of other things. They're all measures of how much more collector current flows than the base current you use to control it.

And that's how it works. There's a lot of other stuff. The collector-base and base-emitter junctions are not identical anymore like they once were because we found out that we can make them different to one side and get much higher collector blocking voltages and higher current gain. The time it takes to sweep out the base charge is a fundamental limit on how fast the transistor can switch. The separated charges at the collector and base act like a capacitor and limit frequency response. The slight resistances of the leads add parasitic resistances. Lots of stuff.

But it works because there is a reverse biased junction that is "poisoned" into conducting by shooting charge in "sideways" into the blocking region.

[ESPm2M]

Yeah, a turorial page would be a great thing to do!

I agree!

heh hemm... Aron, any thoughts? Can we help gather info?

[Peter Snowberg]

Start gathering.... I'll post it in the FAQ.

[Samuel]

Along those same lines, how about a categorized book referral list. With categories like:

General Elec.
Transistor info
Tube info
General audio stuff
etc. etc. etc.

[niftydog]

EDIT; reposted under unique topic heading "FAQ: Electroincs Tutorials"

Integrated Publishing - fantastic resource Best to search this site for what you want, the indexing doesn't reveal it's depth. Covers a huge range of topics, not just electronics!

ePanorama.net general links - many, many varied subjects

Lessons In Electronics Circuits - very good same mirrored here

Educyclopedia - loads of links by category

Ian Purdies Electronics Tutorials

Alex Pounds Electronics Tutorial

Capacitor Guide

Capacitor Tutorial

Resistor colour code calculator

Also, don't forget the manufacturers, they often have very good application notes and design guides:

National

Fairchild

Texas Inst.

Analog Devices

Maxim
(Maxim application notes page)

Philips

ON semiconductor

and many more, easily found.

[Steben]

The amount of collector current that flows per amount of base current is called the current gain, hFE, HFE, lots of other things. They're all measures of how much more collector current flows than the base current you use to control it.

Nice speech
hFE stands for AC gain, HFE for DC gain. For musical purposes hFE is the most important, HFE is usually a bit higher.
hFE Germs: 60-150
hFE Silics: 90-600
hFE Power Silics: 25-100[/quote]

[ESPm2M]

Along those same lines, how about a categorized book referral list. With categories like:

General Elec.
Transistor info
Tube info
General audio stuff
etc. etc. etc.

No objections here.  These would both make the forum an even better resource.

[ESPm2M]

Should start a new thread for people to contribute to the gather of info for these new resources?

[Toney]

Hi,
my computer has been offline due to a tidalwave of spam.
Fixed now, but I want to thank all those who patiently contributed to a new guys understanding.
As someone trying to get a conceptual grasp of the function of transistors, I found the Educypedia links that niftydog posted particularly illuminating.So if you do compile a tutorial on this subject, I think that it would be a valid reference.
And to think, last week I just thought I'd do some surfing for a pedal that could "honk" .......