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From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Newsgroups: sci.electronics.design
Subject: Re: kids these days
Date: Mon, 30 Sep 2024 15:51:38 -0000 (UTC)
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john larkin <JL@gct.com> wrote:
> On Mon, 30 Sep 2024 11:13:56 +0100, Cursitor Doom <cd@notformail.com>
> wrote:
> 
>> On Mon, 30 Sep 2024 05:15:02 GMT, Jan Panteltje <alien@comet.invalid>
>> wrote:
>> 
>>> On a sunny day (Sun, 29 Sep 2024 10:36:26 -0700) it happened john larkin
>>> <JL@gct.com> wrote in <kb3jfjpejs47hqjd00fis20eog8de19ae8@4ax.com>:
>>> 
>>>> I wouldn't hire someone who complicates a simple question into
>>>> paralysis.
>>>> 
>>>> 
>>>> I draw a 10 volt battery connected to two resistors, 9K in series with 1K.
>>> 
>>> The problem there is 'draw', no reality.
>>> The battery will have an internal resistance, maybe discharged too.
>>> 
>>>> What's the voltage across the 1K?
>>> 
>>> 
>>> 
>>>> I hired a 3-month intern a month ago who failed the test. He said 9
>>>> volts. I hired him anyway and fired him as an intern on Friday. He's
>>>> full time now. He's mostly a software engineer. I'm teaching him basic
>>>> electronics now. 
>>> 
>>> Well, that is OK.
>>> But needs experimenting, building circuits, else all vaporware.
>>> Same with software, write it, test it, else just imagination...
>>> It may not be / work for everybody..
>>> Some run for US precedent..
>>> When I have to believe the crap trump puts out these days (about Iran for example)
>>> 4 sure (or maybe even 00 sure <where 00 is the symbol for infinite> ) we will have
>>> WW3 no matter who is winning the electtions.
>>> 
>>> 
>>>> I dream of some day finding a kid who gets the voltage divider right
>>>> and has something intelligent so say about the next test, an NPN
>>>> emitter follower. 
>>> 
>>> Ge or Si?
>> 
>> John mentioned a Vb of 0.6V so the 'student' is expected to know it's
>> silicon. And of course, it's a Vbe of 0.6V and that distinction seems
>> to trip up a lot of young folks, it seems. The Vb is 5. Once they get
>> that straight, the rest of it falls into place easily enough. Should
>> take < 30s for someone to figure out - and hopefully <<!
> 
> No, I said that one EE grad claimed that Vb (not Vbe) would be 0.6
> volts to ground.
> 
> Can anyone here say about what the base and emitter voltages actually
> are? Collector current?
> 
> +10 supply, two 10Ks making a divider into the base, 1K emitter to
> ground, typical small silicon NPN.
> 
> Extra credit: anything else to say?
> 
> 
Standard ROT circuit from technician school BITD. 

Beta of 200ish, roughly 4 mA I_C, so the base pulls 20 uA. With a 5k
source, it’ll sag 100 mV, not much. 

So V_E will be near 4.3 V, unless it oscillates, which it probably won’t
unless it’s built on one of those nasty white nylon slab things. 

(Technician school is particularly insistent on the distinction between
beta and beta+1 in circuits, even though datasheet limits easily exceed
2:1.)

Cheers 

Phil Hobbs 


(who’s never taken a circuits course other than “RLCs for physicists”)

-- 
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics