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Charge Conservation - Hint of the Day

See my preface. The notion of "delivered charge" crops up pretty consistently in electrical engineering, and it almost always means "charge delivered to (some lead of) some component (while ignoring charge coming out of one or more other leads)".

If you're willing to do more math, and to posit a switch that magically opens when current drops to zero, without itself having any voltage drop, then you can get exactly the same results (i.e. -- the total delivered charge is limited by your desire or the total resistance in the circuit) by having the inductor charging up a capacitor (which will have no more net charge when the process is done than when it started).

Or replace the switch by a real-world diode, and find that the total charge that will flow through the inductor is limited by the diode's characteristics as well as the rest of the circuit.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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Reply to
Tim Wescott
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For example, from _Consumer_Reports_, "Used Cars to Avoid": Audi;

In the Best Used Cars List: Infiniti Q45 ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
Reply to
Jim Thompson

"Schlocky" is constructing a riddle with multiple interpretations so that no matter which answer the victim gives, the perpetrator can cackle (or cluck, in some cases) from his position of "wisdom". This is a trick often played by college sophomores engineering nerds on their freshman dorm-mates.

Reply to
Richard Henry

On a sunny day (Wed, 21 Jul 2010 10:15:51 -0700) it happened Jim Thompson wrote in :

Bull. You mean 'specified conditions'. 'All ...' would mean also when the sun burns out. Clue, clue clue Where is yours?

Reply to
Jan Panteltje

Am I to suppose all of his linear ICs will work at liquid helium temperatures, or at 350C?

John

Reply to
John Larkin

=A0 =A0 ...Jim Thompson

Q =3D the limit, as V goes to zero, of 10 mJ/V

.
Reply to
tlbs101

=A0 =A0 ...Jim Thompson

Oops... ,make that 1 mJ/V

Tom Pounds Albuquerque

Reply to
tlbs101

Oh gawd, the number of non-technical people I've met who want to consider engineering a 'soft' discipline, like a belief system :)

Had a wonderful argument once with a lady about her 'faulty' photocopier, she regularly emptied and filled the toner overflow container, and was wondering why the copies kept getting fainter and fainter... Yet after a service call, the copier worked fine!

I discovered her error by asking to watch how she added the toner, then the penny dropped -- yet the instructions for adding toner were printed right there under the lid of the copier.

Often I 'fix' things simply by following the instructions ;)

Same with electronics design, one gets amazing results by following the datasheet and applications notes -- then bending the circuit to meet requirements.

So yeah, working with a vague query means you get to make up the ground rules in your response, hopefully in a way that lets others follow your reasoning and therefore able to duplicate your results, or point out any flaw in reasoning -- basic scientific method, we follow certain rules that can be verified by experiment -- hard evidence vs some belief system.

Even if one argues some of the tools are belief systems (valid until proven wrong), the models we use at least work close enough to reality to be useful.

It's the playing with magic smoke :o) Dance of the universe.

I know one can charge an inductor, look at the lovely sparks one may produce with them!

Replying to Jan, too. Philosophical.

Grant.

Reply to
Grant

What a complete waste of bandwidth.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
Reply to
Phil Hobbs

At specification temperatures, you pimp.

Actually some of my designs do work "down-hole". Schlumberger loves me :-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

                   Spice is like a sports car... 
           Only as good as the person behind the wheel.
Reply to
Jim Thompson

Are you a supplicant ?:-) ...Jim Thompson

-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

formatting link
| 1962 |

Spice is like a sports car... Only as good as the person behind the wheel.

Reply to
Jim Thompson

Looks like an energy conservation issue rather than charge conservation, unless the answer is meant to be zero as suggested by one respondent.

Stick a capacitor across the inductor and the charge passed through the capacitor will depend on its capacitance, as will the potential difference obtained. However, the total energy transferred to the capacitor (at the point where the current drops to zero) will be a constant.

Sylvia.

Reply to
Sylvia Else

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Yeah sure, I use the same words. But isn't this the cause of the current .... 'confusion'?

NPI

It's kinda like the water in a hose analogy of current in circuits. It mostly works... but you can't spray charge out the end of a circuit, you've gotta have a conductor attached. (let's assume no high voltages.)

We really only measure voltages and currents, we all know there are charges moving around, but as soon as you try and get them to hold still they disappear. (Well you can use a Faraday bucket.)

I've been looking at flux leakage with our Keithley 601B electrometer. At the 10^11 ohms scale (with the multiplier set at X10 or X30) I can't walk near the circuit with out upsetting things.

George H.

Reply to
George Herold

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Yes thanks, I don't have any real problem with the notion of delivered charge. I use the same words/ideas all the time. Electrons buzz all about in our circuits. But charge conservation on a capacitor is not ussually important. (Isn't this JT's notion?)

George H.

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Reply to
George Herold

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Reply to
George Herold

I have a 610C

ftp://jjlarkin.lmi.net/Keithley_1gig.JPG

On the 1e-14 amp range, with just an open Pomona plug as an antenna, I can shuffle my feet on the carpet 10 feet away and pin the meter.

Beautiful gadget.

John

Reply to
John Larkin

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Opps, the number is 610B. (I'm always getting the numbers confused.) I've only got a 1 Gohm resistor to check the 'calibration' with. But it seems to work great. I'll post a flux report over on SEB. (bottom line, all rosin based fluxes seem to work fine for high impedance circuits. )

George H.

Reply to
George Herold

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resistance.

The Keithley manual says to replace the high-value resistors every

*six months*. I got mine off ebay and I bet it's been a while. It looks to me like my high-end ohms measurements are a bit high; a 1T resistor, which is probably OK, reads about 1.4T. Some day I may replace a few resistors with more modern parts which, I hope, will drift less.

Roger rosin flux. On some of our impedance-sensitive boards, we specify rosin flux paste solder and organic solvent wash. We do that in-house, but if we send stuff for assembly out it's hard to find anybody who hasn't gone all water-based.

John

Reply to
John Larkin

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Ahh, the resistors in this thing are as old as the hills. It's been sitting on a shelf collecting dust for at least eight years. Back in

2002 the boss was trying to do some field emmision measurments, but we couldn't get a good enough vacuum.

The 10^9 ohm scale looks good, but 10^10 is high by ~10% and 10^11 is high by maybe 30%. This is with the meter multiplier in the x0.1 position, with 1 G ohm across the input. The end of the meter needle is oscillating like crazy.. maybe +/- 5%. I must be seeing electric fields in the room... 60Hz AC maybe?

George H.

Reply to
George Herold

it.

resistance.

Is there a proviso: uncooked rosin? Dark overheated rosin looks leaky to me, imagining a high carbon content.

Grant.

Reply to
Grant

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