Driver to drive?

K8JLF · Dec 6, 2004

FWIW, 24V is still used in the US to power some cellular site and other telecom
equipment. I think it was -24V.

Dr. Slick · Dec 6, 2004

Winfield Hill <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote in message news:<cp0ds007jp@drn.newsguy.com>...

Two comments with respect to datasheets. First, beta is easy for
a manufacturer to measure and bracket its value range. Designers
find this useful to estimate best-case / worst-case base currents
after setup and biasing the transistor using Vbe. For example, it
tells him the worst-case base drive capability to allow in a power
emitter follower, or how much base current (error) he may encounter
in an opamp input stage, etc. Knowing how poor the beta parameter
is, the designer strives to eliminate its effect in a circuit, but
it's still useful to know its min-max range to evaluate the design.

Second, one will never find Ebers-Moll transconductance parameters
in a datasheet, because being absolutely predicted by kT/qIc, and
identical for all BJTs, no value would come from printing this
redundantly in a datasheet. (As CBarn24050 says, one often doesn't
even need the datasheet to make a good design). One may find Vbe
at a given current and temperature, thereby fixing a basic current-
density property for that transistor type. But a designer may have
to estimate this value, based on knowledge and experience, or use a
set of typical Vbe vs Ic curves in the datasheet, but you will find
this is not normally an impediment to completing a design.

Want an BJT CCCS circuit? Add an emitter resistor and analyse with
Ebers-Moll and get a predictable collector current, reliable, ready
for production. Leave out the emitter resistor and rely on beta to
program the collector, and YOU DARE NOT use that in production!

So you mean add a "series feedback" resistor
to the source (equivalent to adding a resistor to the
source in a mosfet). But how about using shunt feedback?
Or a voltage divider for the base, to make
the circuit Beta-independent?

With all due respect for writing a popular
teaching text, a good part of your book (and
most other basic circuit texts)was devoted to biasing a
bjt to be Beta-independent.

ALL of the industry uses Beta to describe a
BJT in the data sheets, and NEVER transconductance.

Also, on page. 113 of The Art of Electronics:

Concerning an npn BJT: "This results in a
collector current, CONTROLLED by a (smaller)
base current."

Maybe this chapter was written by Horowitz?

Slick

Dec 6, 2004

It helps if you click [View With Title Only]

I can't see any way to put it in a monospace font.

I'm posting this having logged in first to see if it's attributed to my
display name and not my (truncated) e-mail address as my last post was.
On the plus side, posts appear almost immediately !

Winfield Hill · Dec 6, 2004

John Larkin wrote...

Winfield Hill wrote:

Second, one will never find Ebers-Moll transconductance parameters
in a datasheet, because being absolutely predicted by kT/qIc,

A 2N2222 has a transconductance roughly 1/15 this value at 500 mA.
Vbe is around 1.3 volts, according to the old green Motorola databook.

Beta, on the other hand, is only down to about 0.4 of its peak value
at the same current.

Your point being?

--
Thanks,
- Win

Winfield Hill · Dec 6, 2004

Mike Monett wrote...

And you can let them know how much you like the new interface here:

http://groups-beta.google.com/support

I didn't see a place where they invite feedback. Here Google
introduces Google Groups, as a competitor to Yahoo Groups, etc.
But they fail to make clear that your own custom Google Group
is not a part of usenet, and will not appear on usenet servers
all over the world. Furthermore, they show the entire scene of
usenet groups as if these are merely thousands of other Google
Groups, like your own custom-created Google Group.

--
Thanks,
- Win

Guy Macon · Dec 6, 2004

David L. Jones wrote:

2) You can get used Rubidium standards on eBay,

Here is one in the $250 to $350 range:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3856526769

Leon Heller · Dec 6, 2004

"Norm Dresner" <ndrez@att.net> wrote in message
news:vGSsd.1039376$Gx4.339941@bgtnsc04-news.ops.worldnet.att.net...

There are many inexpensive, so-called "atomic clocks" in the mass market
which AIUI use something like the NIST radio sites to do the time setting.
Is it possible to hack into one of these and extract a signal that could
be
used for calibration of instruments. I'm not looking for "NIST Traceable"
but just something to calibrate a bunch of frequency meters to a
reasonable
standard.

Try this: http://www.geocities.com/icdx_australia/poor_mans_caesiumclock.htm

I keep meaning to build an updated version with a CPLD replacing the 74HC
logic.

Leon

Winfield Hill · Dec 6, 2004

Kevin Aylward wrote...

If you have ever read an advanced group theory algebra book
it should be obvious that sometimes being economical with
the truth can be useful.

Maybe that's why I found group theory to be so difficult.

--
Thanks,
- Win

Robin · Dec 6, 2004

Win wrote:-

I didn't see a place where they invite feedback.

Nor did I so I asked them about this in the ask-us-a-question box (at
the bottom).

Cheers
Robin

alan · Dec 6, 2004

Mike Monett wrote:

And you can let them know how much you like the new interface here:

http://groups-beta.google.com/support

Best Wishes,

Mike Monett

They already got a huge amount of negative feedback, and they went ahead
and did it anyway?!?!

Jim Thompson · Dec 6, 2004

On 06 Dec 2004 04:02:02 GMT, chrisgibbogibson@aol.com
(ChrisGibboGibson) wrote:

[snip]

I don't think anyone will get very close. But I think the VC brigade will get a
lot close than the CC brigade.

Gibbo

480)460-2350 | |
| E-mail Address at Website Fax

Kevin Aylward · Dec 6, 2004

Winfield Hill wrote:

Kevin Aylward wrote...

If you have ever read an advanced group theory algebra book
it should be obvious that sometimes being economical with
the truth can be useful.

Maybe that's why I found group theory to be so difficult.

That's why I said "read", not "understand".

Ohh...and you never mentioned my comparison to you with S. Hawking

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

John Larkin · Dec 6, 2004

On Mon, 06 Dec 2004 12:18:37 GMT, "Kevin Aylward"
<salesEXTRACT@anasoft.co.uk> wrote:

And how does this contradict the view that the bipolar transistor is
voltage *controlled* which has the nuisance of dealing with the *effect*
of base current?

Base current is not an effect if you jam it in.

John

Nico Coesel · Dec 6, 2004

"Norm Dresner" <ndrez@att.net> wrote:

There are many inexpensive, so-called "atomic clocks" in the mass market
which AIUI use something like the NIST radio sites to do the time setting.
Is it possible to hack into one of these and extract a signal that could be
used for calibration of instruments. I'm not looking for "NIST Traceable"
but just something to calibrate a bunch of frequency meters to a reasonable
standard.

Use the carrier of a radio or TV station. These are usually very
stable.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl

Joerg · Dec 6, 2004

Hi Jim,

I just give my dogs twisted rawhide sticks.

We also used to do that until our big one almost died after a chunk of
that got stuck in his intestines. At least that's what the vet suspected
after finishing the surgery.

Regards, Joerg

http://www.analogconsultants.com

John Larkin · Dec 6, 2004

On Mon, 06 Dec 2004 18:21:54 GMT, "Kevin Aylward"
<salesEXTRACT@anasoft.co.uk> wrote:

Excluding magnetic effects, base current is always due to a voltage, the
only way to force a current to use a *voltage* feeding a resister, or
another transistor used as a current source, which in turn is voltage
controlled.

Are you claiming that the only way to create a current is by using a
voltage? Shocking, shocking!

John

Winfield Hill · Dec 6, 2004

John Larkin wrote...

Are you claiming that the only way to create a current
is by using a voltage? Shocking, shocking!

Hey, not _that_ much voltage!

--
Thanks,
- Win

Arie de Muynck · Dec 6, 2004

"Ross Herbert" ...

Thanks, nice references!

--
Regards,
Arie de Muynck

John Larkin · Dec 7, 2004

On Mon, 06 Dec 2004 17:43:19 -0700, Jim Thompson
<thegreatone@example.com> wrote:

On 6 Dec 2004 16:17:49 -0800, radio913@aol.com wrote:

[snip]

This has already been explained. Transconductance is the same for all
transistor, so why state it?

Bullshit! Gm is the same for all transistors?

It's not even the same for a single transistor, let
alone many of them!

[snip]
Slick

Sorry to burst your bubble, but gm (for a BJT) is only a function of
current, and NOT the size of the device.

...Jim Thompson

Compare the Gm of, say, a 2N918 to a 2N3055, both at 200 mA.

Hah!

John

Winfield Hill · Dec 7, 2004

Jim Thompson wrote...

Sorry to burst your bubble, but gm (for a BJT) is only
a function of current, and NOT the size of the device.

Right, assuming Is is constant across the devices...
(Someone always has to play the devil's advocate).

--
Thanks,
- Win

Driver to drive?

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