A DAMPING CIRCUIT FOR A COIL

[Aziz]

deemon used a BY359.
I found an interesting link, on "damping", a couple of weeks ago. Its here : http://www.earlytelevision.org/damper.html

That's a nice link. Thanks!
Aziz

[moodz]

Eeehhhhh moodz,

20dB ain't 100 times. 20 dB = 10 times.
( 10^(20/20) = 10^1 = 10 )
But still more than what we have today.

Comeon, put a nice spice file. Please! Pleeeaseeeee!!!!

Aziz

http://www.sengpielaudio.com/calcula...lification.htm ... Eeeeeeeh Aziz ... I only ever use power gain not voltage gain ( that is for hifi sales guys ) ... the figure of 100 is accurate for power gain .... the voltage gain would be 40db ... eg a 1 euro coin placed in the centre of an 18 inch coil will rail the first amplifier. :-)

[moodz]

...the reason for this high gain is that the constant current load / sink turns into a "common gate amplifier" after the feedback impedance ( diode ) on the source goes open circuit after the flyback voltage approaches 0 volts with respect to coil "ground" this gain multiplied by the first op-amp coupled with squared response at the "loop balance" point results in huge target signal gains. (A x B)squared where A is gain of current sink B is gain of first amplifier ( the loop amplifier ) all squared. :-) .... can result in as much as 30% increase in depth depending on ground. The ground response and target response is modified by the non-exponential decay now ... this means that you could sample at 20 microseconds on a typical coil and still detect a 0.1 gram nugget ... this is proven by experiment.... of course sampling at the optimal time will be alot better for an 0.1 grammer ( which would be around 4.5 usec with a 200volt flyback, 400 usec tx, 3 amp current and 0.4 ohm 300 uh coil ). The real eye opener is letting the flyback voltage go up to say 1000 volts ....you can then damp the coil approaching 1 microsecond and even when the coil is heavily loaded with say 1000 puff of capacitance in parallel. This indicates that whilst winding low capacitance fast coils is useful for resistively damped circuits it is not as critical for the current sink damped circuit ... though more tests are required to define these benefits.

[hdphilip]

The summary benefits are much faster damping thus resulting in earlier sampling, greatly improved SNR , inherent EMI rejection, ability to "auto tune" to optimize most any coil and the elimination of all prior art claims relating to ground balance and sampling

moodz,

so this circuit takes care of ground balance, in which has been described in conventional theories?

also, are you going to make a PCB and sell you idea as a "add on" board, so the "surf pi" following could upgrade their kits?

or

is a whole new front end required?


philip

[Qiaozhi]

Following on from Carl's admonishment of Paul99 (and Moodz's request to keep this thread clean) I have deleted a few other off-topic posts / comments, and the provocative string of Minelab logos in Aziz's posts.

To Aziz: - Please don't keep trying to test the limits, as you're in grave danger of finding them. Stop mentioning ML, and asking if this is the end. If you don't like the company, then don't buy their products.

Also, this is not an excuse for you to start another off-topic discussion. Any replies to this post will be removed.

[moodz]

moodz,

so this circuit takes care of ground balance, in which has been described in conventional theories?

also, are you going to make a PCB and sell you idea as a "add on" board, so the "surf pi" following could upgrade their kits?

or

is a whole new front end required?


philip

You could add it to the surf PI but it would be better to re-layout the surfPI with the new front-end incorporated however I not sure how the lack of precise TX timing source would affect the circuit. The ground balance still has to be done .... its just not as hard :-) ... thats a pun philip ... hard ground ... get it .... mehhh its a tough room tonite. :-)

[greylourie]

For people like me, Google books has some information on "damping diodes". Pulse and Digital Circuits by Prakash Rao ISBN 0070606560. See pages 232 - 233. (Rao published another edition quite soon after the book I mentioned.)

[Davor]

moodz, can you please post the patent number - I'm a bit lost.

[moodz]

moodz, can you please post the patent number - I'm a bit lost.

http://www.ipaustralia.com.au/applic.../AU2013101058/

[Qiaozhi]

You can download the full patent from here ->
http://www.google.co.uk/url?sa=t&rct...53899372,d.d2k

[Davor]

Thanks. OZ patents tend to be confusing.

[moodz]

... a variation of my design ...

...the servo loop in the patent can be dispensed with and a fixed bias on the pass mosfet can be used instead as per the following example .... there is a conventional damping resistor used ( because the current sink is not functional ) Instead of using a messy frontend switch to block the flyback voltage we use the flyback voltage itself to do the switching. The 10 volt bias on the gate of pass mosfet M2 ensures it is hard on except during the flyback period ... note that this bias is higher than the TX voltage of 5 volts. D2 and D9 form a snubber which could be 200volts for example depending on the zener value. A high voltage cap in parallel with D2 will help the snubbing function. D3 prevents excessive negative excursions. W1 is the mosfet sampling switch or you could put the amp here .... The main benefits of this circuit are flyback voltage blocking, no need for switching, low impedance path from coil to first amplifier and simplicity and it may be covered by one or more patents.

[Davor]

Funny thing is that I once played with a biassed diode bridge limiter which in effect does pretty much the same thing. Big difference though is that diodes' dynamic resistance is not as small as mosfet's so your solution is far better in a serious build. But it may be interesting for speeding up surfs and baracudas where input impedance is not critical.

[moodz]

...the servo loop in the patent can be dispensed with and a fixed bias on the pass mosfet can be used instead as per the following example .... there is a conventional damping resistor used ( because the current sink is not functional ) Instead of using a messy frontend switch to block the flyback voltage we use the flyback voltage itself to do the switching. The 10 volt bias on the gate of pass mosfet M2 ensures it is hard on except during the flyback period ... note that this bias is higher than the TX voltage of 5 volts. D2 and D9 form a snubber which could be 200volts for example depending on the zener value. A high voltage cap in parallel with D2 will help the snubbing function. D3 prevents excessive negative excursions. W1 is the mosfet sampling switch or you could put the amp here .... The main benefits of this circuit are flyback voltage blocking, no need for switching, low impedance path from coil to first amplifier and simplicity and it may be covered by one or more patents.

...this circuit is not quite as good as the full servo loop but still provides superb performance on a traditional pi design.....obviously you can tinker with the component values to optimise further.

[Tepco]

I smell trouble with this. Reading all this carefully, i'm pretty confident there are some issues whit method described, namely it may not work with real coils in all cases, as in simulation. Issue#1 (main one): this is fine for ideal, lumped element coil, but real coil is distributed parameter circuit, and fastest way to discharge it is by resistive load. Circuit will not “source” energy any faster than limited by natural LC, so cannot be “sinked” any faster with current sink, in effect highly nonlinear resistance during discharge period. Maybe I’m wrong on this, never tried, just my opinion.