difference between bipolar and mosfet

Oh, your assignment question? Listen, Junior, that's for your teacher to explain to you. I owe you no such favors. Stick with your studies, though; you may make it one day - if *you* work through your own homework instead of trying to trick others into doing it for you.

"Of course they're wrong, but so what?"???? The mind boggles. I do appreciate the dilemma, though. On the one hand we'd like to convey a complete understanding of the subject to the questioner. On the other hand, we suspect that if we did so, they'd find it all too much, be turned off and simply find another hobby to pursue.

Perhaps the answer is to provide the simpler explanation, based on the questioner's level of knowledge, but spell out the caveat that there is more to the topic than has been explained in the follow-up. IOW, tell the questioner that the answer provided is sufficient for their current purposes, but they may need to take more on board as they advance in their studies.

Translation: "My ass can't take no more whuppin' so I'm outa here!"

[snip pointless, uncalled-for lecture on base current but maybe some newbie can make use of it]

I've been posting to Usenet for many years, but normally use X-no-archive or my nickname or whatever. Some of the views I put forward on political matters are sadly not regarded as acceptable these days, so when needs must....

Really? So what is it you're taking issue with? Taken as a generalization for most silicon diodes I can't see real problem with it.

It can hardly be described as "disturbing" FFS. Excuse me for not having the time or inclination to wade through your entire post and answer every individual point; but if you're trying to suggest that I'm as guilty as you in giving 'easy' and expedient explanations to newbies that don't reflect the full picture, then I guess I'd have to plead guilty. None of us are perfect. If you don't like it, sue me. :P

You've pre-empted my considered view on the matter (see my posting of earlier today further up the thread).

The boggling threshold, of course, varies with the individual mind in question...

Precisely my point.

You DID read everything I wrote, right? I believe I said exactly that.

Bob M.

thats ok, i am enjoying it!

-

No, a sarchasm is where they tossed all those poor unfortunate chickens in China and Hong Kong a couple of years back....:-)

Sorry to interrupt this little lovefest here...I'll go back to my knitting now....

Bob M.

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Puh-leeze!!! Now you're second-guessing Google and all the other
archivists?  I suggest you take care of your own business and let
everyone else take care of theirs.

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Nothing of the kind.  Kevin and I have been at loggerheads with each
other more than once in the past, and he knows that I have a great
deal of respect and affection for him, so your disingenuous
"refereeing" falls on deaf ears.  However, _your_ sickening pomposity
has been noted.

--
Waking up in the morning knowing you've got email waiting does it for
you, I expect;)  Anyway, what's 'sarchasm'?  Sounds like something you
fall into when you can't figure out the insult...

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Hogwash.

All work and no play is _not_ a good thing.

--
Casting purls before swine?^)

Storage, OTOH, isn't as cheap and we can all snip a lot more savagely to make life easier for Google and other archivists.

Sadly, pointing out the truth about certain things in this world is no longer acceptable. Political-correctness and such like. It's slowly getting worse, too. For some factual historical views one can even risk imprisonment and have one's carreer and livelihood destroyed. The views are too important to hide, so they have to be disseminated by stealth. It requires that certain precautions be taken. A shameful situation, I grant you.

As I recall (dimly) high winds cutting across the bridge built up a series of increasingly violent osicallations, resulting in its total destruction. Are you trying to say a diode would oscillate itself to destruction? I've noticed you're not very good with analogies so I'm afraid whatever your beef is, you're gonna have to spell it out in plain English....

No idea what you're talking about, I'm afraid, Old Fruit.

Well it appears that Kevin has straightened out your misconceptions about how a transistor works and set you on the right road to further studies on a firm foundation. I suppose it's too much to expect you to show him an ounce of gratitude for his (considerable) time and trouble. :-(

No problem. Being a seasoned Usenetter of some 13 years standing, it takes a bit more than mild sarchasm to give me a bad day ;->

Work hard on your studies, Junior. Nothing comes easy in this life except to the very fortunate.

Put it out of your mind as a pointless distraction, sonny and get stuck back into your textbooks. Head down and study, study, study is the only realistic way to success. HTH

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Apology accepted.

--- Hardly. Your statement:

"Sadly, pointing out the truth about certain things in this world is no longer acceptable. Political-correctness and such like. It's slowly getting worse, too. For some factual historical views one can even risk imprisonment and have one's carreer and livelihood destroyed. The views are too important to hide, so they have to be disseminated by stealth. It requires that certain precautions be taken. A shameful situation, I grant you."

contains no mention of the method of anonymity you use, hiding, which you admit to later on in the post to which I'm currently replying.

Consequently, it's not a question of lack of comprehension on my part, but a lack of clarity on yours.

However, I should have guessed that would be your method of choice judging from the bob-and-weave tactics you've employed in your earlier posts.

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--- If you have to hide to preserve your liberty then you have no liberty to preserve.

---

--- Uh-huh...

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--- More bob-and-weave, huh?

The point wasn't that the change in drop was a large percentage of the drop at the knee, it was that the change in drop was small compared to the large change in current through the diode. If you recall, the application was inserting a silicon diode or two in series with a power supply in order to realize the ~ 0.7V drop each diode would yield with the device operating, to which you responded with:

"Um, yeah, but they drop voltage _according_ to current! If they're dropping 0,7V., they're not passing much current! Diodes are a crap way to drop voltage unless the load is light and predictable!!!"

which _is_ crap since, in the first place, the load current will be predictable since it will vary between two limits and, in the second place, the drop across the diode with the variations in load current and junction temperature will also be predictable.

For example, a 1N5400 will drop about 0.7V with about 100mA through the junction, but that drop will only increase by 200mV for an increase in current to 3A.

Likewise, a 1N3491 will drop about 0.7V with 100mA through the junction, but with 0.9V across the junction the current through the diode will be about 8 amps.

So, in the first case, if a 200mV change in input voltage to a load can be tolerated for a load current change of 3 amps, it'll work fine.

In the second case, an 8 amp change in load current will cause a change of only 200 mV in the drop across the diode. Not exactly what I'd call a 'light' load, and all of it predictable.

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--- Well, IME, for the same If, Vf depends on what the diode's made of.

Easy enough to check it out... get yourself a 9V battery, a 20K rheostat, a silicon junction diode, a Schottky diode, a 0-1mA ammeter and a 0-1V voltmeter. Making sure you have the rheostat cranked to the max resistance position, connect everything up like this:

+9V | [R] | +----->>----+ |A | [DUT] [0->1V] | | +----->>----+ | [0->1mA] | -9V

Then, adjust the rheostat to the position required to make the milliammeter read 1mA, note whether the DUT is the Schottky or not and write that down along with the voltage indicated by the voltmeter when the milliammeter reads 1mA. Do the same thing using the remaining diode and report back to us with what you find, OK?

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--- Before you can determine whether or not someone knows how a BJT works, you need to know how a diode works. You haven't demonstrated any real competence in that arena, so I suggest you do the experiment I described and see what you can learn from it.

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--- Before you start making noises about who knows what about BJTs you really ought to get that diode theory down.

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--- So, the obvious you don't have much trouble with?

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--- Go for it!

-- John Fields