Rethinking our approach to the DDL?

lasersbee said:

I understand what HIMNL is saying...
You can not have current without voltage AND resistance...
and yet you are saying that is not so..

Click to expand...

Measuring current without any resistance or voltage drop is actually pretty easy: If you know the dimensions of a superconducting magnet coild like those in an NMR machine, you only need to measure field strength to determine the circulating current in the coil.

This is somewhat comparable to measuring voltage using a voltmeter: The meter will put a tiny load on the magnetic field, just as a multimeter will always draw a minute amount of current from whatever voltage source you are measuring.

Also, the Ampere is a SI base unit, the Volt is not.

^ Finally, someone on my side!

Benm said:

Measuring current without any resistance or voltage drop is actually pretty easy: If you know the dimensions of a superconducting magnet coild like those in an NMR machine, you only need to measure field strength to determine the circulating current in the coil.

This is somewhat comparable to measuring voltage using a voltmeter: The meter will put a tiny load on the magnetic field, just as a multimeter will always draw a minute amount of current from whatever voltage source you are measuring.

Also, the Ampere is a SI base unit, the Volt is not.

Click to expand...

I'm fairly sure we were discussing current as in a low current
(<5A) DDL type Laser Driver and not the massive current as in
a NMR or MRI Machine's sensing coil....:yh:


Jerry

Benm said:

Measuring current without any resistance or voltage drop is actually pretty easy: If you know the dimensions of a superconducting magnet coild like those in an NMR machine, you only need to measure field strength to determine the circulating current in the coil.

This is somewhat comparable to measuring voltage using a voltmeter: The meter will put a tiny load on the magnetic field, just as a multimeter will always draw a minute amount of current from whatever voltage source you are measuring.

Also, the Ampere is a SI base unit, the Volt is not.

Click to expand...

My definition of easy is "cheap".... we have all sorts of current probes at work and the cheapest is around 700 and average is 5k.... Not easy... you may find a cheap one on the web but it won't be tektronics and it won't handle low current.

My wife tells me that I'm a stupid person for butting into an argument; that I should just keep my mouth (and keyboard) quiet... butt...

Voltage exists as a charge (potential) - think electroscope. There is a current (electron flow) when the electroscope is 'charged' but no current when the source of that charge is removed after potential equilibrum (voltage is same.) We could assume a magic material for the charging-rod which has no resistance; and we don't need to leave this universe to witness superconductivity without resistance. So, both voltage and current can exist without resistance. What we would have, however, would be a flow of electrons from the charger to the electroscope in an almost infinitly short time period - EXCEPT, the rod will now create an inductance (based on current flow) which will create a magnetic field which will impede the electron flow... Voltage Leads Current in an Inductor. Eventually, the magnetic field will collapse and the electroscope blades will be at the same charge as the charger - hence no more current flow: therefore, there is a charging time for the electroscope and the electroscope is now acting as a capacitor... or, it can be used to charge another similar electroscope (source) and the outcome will be two electroscopes with 1/2 charge each from the original full-charge.

We need to be careful with Ohm's Law (DC) because like Newton's Law, it has a limited scope of definition in the real-world. With the exception of calculating Power (Watts) generally Ohm's Law neglects time - this is not the case for AC circuits. For anyone that wants a good read at their own pace, look into http://ibiblio.org/kuphaldt/electricCircuits/index.htm

I don't know if anyone is interested, but you can play around with transistors, MOSFETs, diodes, resistors and such for free using the online SPICE program on Circuit Simulator Applet ... I checked and could not find a suitable Laser Diode SPICE definition, but just for doing rough calculations before etching boards and such, the tool is nice. You can even move the entire JAVA model down to your PC and have access even if you are off the Internet. For "canned" routines, check out the "Circuits" tab. If you make changes to a canned-routine, don't forget to File/Export it and copy the definitions into Notepad for saving to your harddisk. Warning: SPICE is too much fun, you will waste a lots of time playing; I'm sorry ;-)

Here is what the typical 4/6 diode load test looks like when applied to the model:
$ 1 5.0E-6 10.20027730826997 50 5.0 50
d 272 48 368 48 1 0.805904783
d 368 48 464 48 1 0.805904783
d 464 48 544 48 1 0.805904783
d 544 48 544 160 1 0.805904783
d 544 160 384 160 1 0.805904783
d 384 160 272 160 1 0.805904783
w 464 48 464 96 0
w 272 48 160 48 0
r 272 160 272 256 0 1.0
g 272 256 272 304 0
w 160 48 160 320 0
S 176 368 176 320 0 0 false 0
w 192 96 192 320 0
w 192 96 464 96 0
w 304 368 176 368 0
w 272 256 432 256 0
w 432 256 432 368 0
v 432 368 304 368 0 0 40.0 7.2 0.0 0.0 0.5
x 145 402 184 408 0 24 SW
x 198 330 242 336 0 24 Red
x 102 336 151 342 0 24 Blue
o 8 64 0 35 5.0 6.4 0 -1

Just copy and paste into the tool using "File / Import"

-Ray

Sorry for the delay, i was offlined.

Well, then, about the voltage ..... explain me how the electrostatic voltmeters can measure voltages without placing any load on the circuit (an electrostatic voltmeter is a totally open circuit, no resistance and no current), if the voltage is not present alone, but only when there is a load ?

Also, resistance is present independently from the fact that you are measuring it, or that you have or not a current through it (100 ohm resistor is 100 ohm value under voltage AND alone on a shelf )

Also, current IS secondary (electrons flow PER time unit ..... still the derivation from 2 other parameters)


@ Jerry: the speed example was from a real cause i presented against a speed ticket in the past (made with "multanova" unit), together with the request of proof that the unit was working good (when they write "device checked and working", it means only that the internal self-test work, not that the measure is accurate), and another pair of things like these ..... the judge had no possibilities to accept totally it, otherwise they had to delete also the other 3600 tickets they gave to other peoples (and they will NEVER accept something similar), but it helped me in passing from 680 Euro and 5 points deleted from the license, to 89 Euro and no points from the license (the minimum in absolute) ..... better than nothing :eg:

Re: "explain me how the electrostatic voltmeters can measure voltages without placing any load on the circuit"

Principle of operation (From Wikipedia): "The electrostatic voltmeter is utilizing the attraction force between two charged surfaces to create a deflection of a pointer directly calibrated in volts. Since the attraction force is the same regardless of the polarity of the charged surfaces (as long as the charge is opposite), the electrostatic voltmeter can measure both direct current and alternating current."

As an analogy, you can measure the potential energy of water (equivalent to voltage) if it were to flow by the effect of gravity by knowing only the liquid density and the drop-height (technically, you also need to know the water temperature, air temperature, etc. if you are looking for a very precise value.) You can measure a static charge (voltage) by accounting for the attraction or repulsion of a "known" charge across a distance without any electron flow (current.) Since the electrons that are responsible for the charge move only on the surface of the object but never make a complete path, there are no electrons moving between the two charged objects; therefore, no current flow... therefore there is no physical component which equates to the DC "R" in the E=IR formula. About Physics.Com gives the definition of current as "Electrical current is a measure of the amount of electrical charge transferred per unit time. It represents the flow of electrons through a conductive material." Note in the definition that there is no mention of "R" since it is not necessary to describe current.

Electrical resistance is anything that impede the flow of electrons - this could be between two conductors or between two charged objects as in the case of lightning between the cloud and Earth (The ionized air is both the conductor and the resistor in this case.) With electrical resistance, heat is the results which is why resistors are rated in watts... or sometimes expressed as Volts * Amperes or VA.) Keep the IE product in R at a level below the resistor dissipation value and all is well; exceed that value and the resistor will overheat or possibly burn-out. Resistance dissipation in watts DC is the IE product or mathematically I^2 x R. But, resistance is not necessary for charge movement or for the existence of current or for the build-up of voltage or even for the measurement of that voltage. It is just that in our world, most of what we witness falls into the realm defined Ohms Law.

In AC electrical theory, at any particular frequency, both capacitors and inductors have resistance to electron flow. Pure resistances, even in AC theory, follow the DC theory and the resistance value does not change with the phase angle of the AC waveform. However, even pure carbon resistors have metallic leads that offer an additional "impeding" to electron flow within high frequency devices.

Wish there were a way to say this without all the words!

-Ray

Super conductors DO NOT have zero resistance, they have near zero (too low to 'measure') resistance. You will have NO electron flow (current) without the potential to push the electrons (voltage). If you 'measure' an electromagnetic field, guess what you are using to make the measurement and display the results...

<Edited to be more respectful to others - Ray>


DATELINE 1911:
Kamerlingh-Onnes, Heike - Hydrogen, Helium, Cooling, Liquid, Low, and Found
Kamerlingh-Onnes studied physics at Groningen and he became professor at Leiden in 1882 he concentrated on the properties of matter at low temperatures. In 1911 he found that metals such as mercury, tin and lead at very low temperatures became superconductors, with near-zero electrical resistance. He won the Nobel Prize in 1913 for his work in low temperature physics - A theoretical explanation of superconductivity had to wait until the work and others in 1957.

DATELINE 1963:
Congressional Record - Google Books
"First it was about liquid hydrogen for the U.S. nuclear-weapons program. But by the 1960's, superconductivity -- in which certain materials have zero electrical resistance at extremely low temperatures -- was a major research interest."

Other references: (see all important graph in the thumbnails)
http://www.w2agz.com/Library/Classi...-20011009 Phys Rev Lett v61n14 1988 p1658.pdf

Added comment:
We advance as humans with our knowledge stretched by ever increasing facts and the simple and accepted morph into the complex and questioned areas. Over time, the complex becomes the norm and we humans march ever forward seeking increasing understanding for that which most accept as understood. We have a desire to become God of our surroundings with the knowledge of everything- it is a relentless pursuit but we will never know it all.

<inappropriate comment removed - blame my regressive gene: My avatar may be closer to real-life than I prefer to consider>

- Ray

LOOK !! ..... i discovered negative resistance ! ..... (hey, where's my Nobel Prize ?)

(sorry, just kidding :crackup

Hahaha ^

Thanks for the laugh...

Science is weird stuff... weird science? In any event, lasers are cutting-edge electronic devices based on what just a few years ago would have been called impossible physics. And the state of the art advances quickly as does our knowledge about the electronics that enable the remarkable physics.

To argue a point to the death is definitely a personally disorder that I have, driven by the intake of far too much caffeine delivered by the most advanced of delivery vehicles - the coffee cup. I'm really much nicer in those few minutes after the 1st cup has brought life back to my sleepy body and before the 4th cup which is the over-the-edge push.

I have edited my last post to remove what appears to be a winning move in a board game because in science we move forward with our knowledge but only a fool would believe that they know-it-all... this fool is humbled and brought back to reality by the laughs.

So as I finish my 1st cup of coffee, I propose a toast and salute E=IR knowing that the second and third cup will remind me that the equation works perfectly in a small range of conditions which account for 99.9% of human perception and that the 'edge' is governed by new science that is ever evolving.

- Ray

Ray,
Because we cannot 'measure' the infinitely large, or infinitely small, does that mean that it does not exist?
Your posts are most stimulating. Much enjoyed.

Where would I buy an IC regulator which can be configured as a constant current source, with zero drop out, or voltage loss??

123splat said:

.....
Where would I buy an IC regulator which can be configured as a constant current source, with zero drop out, or voltage loss??

Click to expand...

In a theoric ideal universe, probably .....

Oh, dear me, I'm on my 4th cup of coffee and typing... there is probably some "law" about typing while under the influence of caffeine.

What is needed is a smart-battery (heck, everything else is "smart") that can only produce a specific current-voltage output. The feedback loop for regulation would be physically built into the cell construction such that stability would be maintained by controlling the output power which would be defined as Volt*Amps. This is contrary to todays batteries as they struggle to maintain a constant voltage over time. (Edit: In thinking more, this is probably a chemistry AND a materials problem; chemistry because we must limit the production (voltage) of free electrons nearly instantaneously and material because we must limit the flow (current) of the electrons in real time.)

Today, we regulate voltage and current external to the power source (battery) so that we must consume energy (watts) to perform the regulation: hence the drop-out problem. I'm thinking that one would need to fully abstract the battery using a DC-DC converter with variable efficiency feedback - thus giving the ability to use both voltage and current feedback simultaneously and in real-time. What we would be doing is essentially building a miniature lab power source with both voltage and current regulation. It would consume power, but essentially from the view of the LD, the current and voltage both would be in lock step and regulated. This would obviously require the removal of the capacitor that we almost universally see across the LD.

Of course, maybe the coffee is doing the talking...

- Ray

We could use a Pulse Width Modulator and variable frequency source to create a kind of AC circuit to charge a capacitor across the LD. The pulse width essentially varies the current that the capacitor can integrate to the LD and the frequency limits the voltage because the capacitor has a reactance (like resistance to in DC) so effectively this provides both voltage and current control. Of course, I have not seen a microprocessor that can do positive rail delivery and source the kind of currents we need without a downstream driver, but the idea is interesting. Back in the old days, car radios used a vibrator (current interrupter) in the power supply... this effectively put the full +12 volts to use! We need something like that today that I can modulate at 10K / second.

Let's Play:

Here is the IMPORT for the simulation (Circuit Simulator Applet)
$ 1 5.0E-6 24.46919322642204 73 5.0 50
v 176 192 176 128 0 5 5000.0 3.6 0.0 0.0 0.5
r 176 128 336 128 0 0.0010
c 336 128 336 192 0 1.0E-6 -2.1670889877428937E-4
w 176 192 336 192 0
d 336 128 384 128 1 0.805904783
d 384 128 416 128 1 0.805904783
d 416 128 448 128 1 0.805904783
d 448 128 480 128 1 0.805904783
r 480 128 480 192 0 1.0
w 480 192 336 192 0
v 176 304 176 240 0 5 10000.0 3.6 0.0 0.0 0.5
r 176 240 336 240 0 0.0010
c 336 240 336 304 0 1.0E-6 0.18028565687841963
w 176 304 336 304 0
d 336 240 384 240 1 0.805904783
d 384 240 416 240 1 0.805904783
d 416 240 448 240 1 0.805904783
d 448 240 480 240 1 0.805904783
r 480 240 480 304 0 1.0
w 480 304 336 304 0
o 8 64 0 39 2.5 0.8 0 -1
o 18 64 0 39 2.5 0.8 1 -1

Notes: This shows a simple positive pulse integration across a cap with a 4-diode/1.0 ohm simulated LD load. I set the maximum pulse to the battery rail of 3.6V but some active device down side of the PWM generator must drive the current to the cap and with that there will be a junction loss. Back to battery chemistry or we need a new power device with no voltage drop. See my comments before the SPICE code.

In the PIC below, GREEN is V and YELLOW is I... The 0.001 resistor is the wiring resistance... like I'm using silver bus-bars!

- Ray

I just stumbled on these regulators today.

http://www.advanced-monolithic.com/pdf/ds1085.pdf

I know you guys were looking for a lower dropout regulator than the lm317, and these seem much improved in that regard, with a higher current capacity as well.