Recycling TX power

[Tepco]

Some tinkering about energy recovery PI. And combined whit ideas already mentioned in another (high voltage PI) tread.

Just not to lose point here, "recovery" like in F1280 means just circulating large reactive current thru the coil, without energy being lost like in standard "flyback" style PI, where it is just turned into heat at different parts. But there is many more.

Charging the coil from some (maybe high) voltage source for some pulse time will produce nearly linear current ramp, discharging it, and recovering energy thru the diodes (or anything else) will take about same time, actually bit less, due to losses. This is not typical LRC flyback network whit dumping resistor etc. So using high enough voltage and very narrow charging pulse, current can be ramped up quite quickly, and then released quickly too, fast linear ramp instead of energy wasting flyback, but fast ramp whit high dB/dT without waiting for coil recovery for sampling. Now question is: Can this actually "speed up" the coil, not actually RLC or LC resonant tank, but distributed LC, using part of the energy already stored (non-recoverable) to reverse parasitic C, beyond sampling speed possible whit normal flyback PI? (instead doing it slower like in ill-fated 1280)

Technically easy to do, microsecond pulses at voltage similar to flyback one, recovery and fast sampling. Doable whit cheap and commonly available components. Not to mention implications to very large coils, they cannot to be built to be "fast" in conventional PI terms, physical limitations etc.

This, in combination whit energy efficiency and high sampling frequency (integrate more samples) looks like win-win combination.

Unfortunately, this is just tinkering, my workbench is crammed whit completely different things i have to finish to schedule, so real life tests will wait for some time, but this will be interesting for sure.

Correct me if i'm misfired something here (posting something truly stupid is not banned by forum rules), best regard, and any idea?

[Tinkerer]

Sorry for schematic quality, best i managed to find print it and use scotch tape. Fisher Impulse is actually bad whit small conductive fast decaying targets (jewelry etc), somewhat unstable (this is static machine), and probably most peculiar metal finding PI contraption so far, completely different from anything else and one of it's kind .TX is not square wave, but bipolar 37.5uS pulse at 5.3333kHz, quartz controlled and fixed. After TX pulse, there is no flyback bang, energy is recovered thru D2, D3, but this process is now much slower than usual .So sample is taken after another 37.5uS and last same amount of time. And this is major disadvantage of this detector, 37.5uS delay is WAY too long, (we are waging wars to get 6-8uS in normal PI detectors). Simply, eddy currents in some targets will decay long before that. Next cycle is identical, whit opposite polarity. Rx use low noise input stage, then signal is AC amplified, synchronously demodulated to get DC, and fed to "Geiger counter" type VCO. I don't have coil data.

Tepco,
thanks for the description and explanation.
Some years ago I got one of the Fisher Impulse detectors for repair. Not having a schematic, I could make no sense of the manner it worked, since it was so different from other PI machines. Yes, I remember of looking for the Flyback, to indicate a functioning TX pulse, and not finding it. Fortunately the fault was a broken wire and I got it to work again without understanding it.
Anyway, it represents the first attempt of recycling power and is interesting in that sense.

Recovering the energy through diodes, works for the energy, but the diode noise is a problem for the RX. Using soft switching diodes like Schottky's helped, in my initial attempts of Flyback recovery.
I am sure that the right choice of diodes (there have been big technological advances in diodes) would help.
the other way would be to use Mosfets. Again, the switching noise is the problem, but with the many, many different Mosfet types available, the right choice probably makes all the difference.
How can we soften the switching of a Mosfet, without slowing the switching down?

Tinkerer

[Tinkerer]

Hi Tinkerer,

indeed, not much people have understood the implications (& advantages) of this little genius transmitter. It's even simpler than a push-pull/H-bridge resonant transmitter (single frequency TX).

I am trying not to get much off-topic. To explain, why the time is relative would indeed be quite off-topic, long-winded, beyond the scope of its extent, ...

But I can give a brief overview (if we focus to the features of this transmitter):
- wide band transmitter
- simple & easy
- flexible to configure for best operation
- gives huge kick to the targets (goes deep, very deep)
- can handle very high coil energy (brute force method)
- high power efficiency (if you pay attention to the few critical parts)

This transmitter is even working in my Very Low Frequency PI laptop metal detector as well (the transmitter is really versatile).

Aziz

Hi Aziz,

I totally agree, the transmitter can be adapted and used for an endless variety of efficient high power pulses. Large single pulses, very short high power pulses or even complex pulse wave forms by combining very short quick succession pulses into larger wave forms.

All this is not new. It has existed and is being used in many applications or PRIOR ART as they call it in the patents.
What we are trying to do is to bring this prior art into the modern technology of amateur designed metal detectors.

Tinkerer

[Tepco]

Hi Tepco,

thanks for the schematic. It is a good place to start with.
I believe the Fisher Impulse was good for small targets, but not very good for larger targets.

It's design is quite different from contemporary PI designs. It's main feature was the low power consumption for a PI.

I think the TX drive is a bi-polar square wave.

Tinkerer

Sorry for schematic quality, best i managed to find print it and use scotch tape. Fisher Impulse is actually bad whit small conductive fast decaying targets (jewelry etc), somewhat unstable (this is static machine), and probably most peculiar metal finding PI contraption so far, completely different from anything else and one of it's kind .TX is not square wave, but bipolar 37.5uS pulse at 5.3333kHz, quartz controlled and fixed. After TX pulse, there is no flyback bang, energy is recovered thru D2, D3, but this process is now much slower than usual .So sample is taken after another 37.5uS and last same amount of time. And this is major disadvantage of this detector, 37.5uS delay is WAY too long, (we are waging wars to get 6-8uS in normal PI detectors). Simply, eddy currents in some targets will decay long before that. Next cycle is identical, whit opposite polarity. Rx use low noise input stage, then signal is AC amplified, synchronously demodulated to get DC, and fed to "Geiger counter" type VCO. I don't have coil data.

[Aziz]

Hi Tinkerer,

indeed, not much people have understood the implications (& advantages) of this little genius transmitter. It's even simpler than a push-pull/H-bridge resonant transmitter (single frequency TX).

I am trying not to get much off-topic. To explain, why the time is relative would indeed be quite off-topic, long-winded, beyond the scope of its extent, ...

But I can give a brief overview (if we focus to the features of this transmitter):
- wide band transmitter
- simple & easy
- flexible to configure for best operation
- gives huge kick to the targets (goes deep, very deep)
- can handle very high coil energy (brute force method)
- high power efficiency (if you pay attention to the few critical parts)

This transmitter is even working in my Very Low Frequency PI laptop metal detector as well (the transmitter is really versatile).

Aziz

[Tinkerer]

Most probably no one will beat this when it comes to efficiency. But way this circuit works (producing something like haversine waveform, period determined w. Ltx and C37) will limit dB/dT, crucial requirement for PI.Or i misunderstood something?Maybe what can be achieved whit this limited dB/dT and circuit efficiecncy may add up and compensate, but coil ohmic resistance at high circulating currents probably will be limiting factor for high power operation.

In the post below I describe some parameters. This is only possible with the "Flyback Saver"

http://www.geotech1.com/forums/showpost.php?p=130007&postcount=32

Of course there are limits, there always are, but I believe we have pushed these limits way beyond the former limits.

Tinkerer

[Tinkerer]

First thing first,schematics:

http://www.4shared.com/document/KOm3...isherpuls.html

Hi Tepco,

thanks for the schematic. It is a good place to start with.
I believe the Fisher Impulse was good for small targets, but not very good for larger targets.

It's design is quite different from contemporary PI designs. It's main feature was the low power consumption for a PI.

I think the TX drive is a bi-polar square wave.

Tinkerer

[Tinkerer]

Ok, my bad.

I admit, that this is not trivial to understand.
Maybe next time to give another hint.

Aziz

Hi Aziz,

it is great that you join the discussion. It has been more than one year since you posted the full explanation of the "Flyback Saver" and nobody seems to have understood its implications.

This is why I thought to start from scratch and slowly ease in to the full power of the design.

The Fisher PI seems a good starting point, because it is the first recycling PI that I know of (there may be others). It has been commercially produced and tried by many.

Tinkerer

[Aziz]

??? What is reltivistic in variation of class E ZVS topology?

Ok, my bad.

I admit, that this is not trivial to understand.
Maybe next time to give another hint.

Aziz

[Tepco]

??? What is reltivistic in variation of class E ZVS topology?

[Aziz]

Most probably no one will beat this when it comes to efficiency. But way this circuit works (producing something like haversine waveform, period determined w. Ltx and C37) will limit dB/dT, crucial requirement for PI.Or i misunderstood something?Maybe what can be achieved whit this limited dB/dT and circuit efficiecncy may add up and compensate, but coil ohmic resistance at high circulating currents probably will be limiting factor for high power operation.

Time is relative (Albert Einstein). Once more.
Time is relative (Albert Einstein). Once more.
Time is relative (Albert Einstein).

Play with dt (delta-time), as time is really relative.

Aziz

[Tepco]

Most probably no one will beat this when it comes to efficiency. But way this circuit works (producing something like haversine waveform, period determined w. Ltx and C37) will limit dB/dT, crucial requirement for PI.Or i misunderstood something?Maybe what can be achieved whit this limited dB/dT and circuit efficiecncy may add up and compensate, but coil ohmic resistance at high circulating currents probably will be limiting factor for high power operation.

[Aziz]

Some comments on the transmitter above:

It is a flyback step-up DC/DC converter (!), which builds a high voltage in the phase 2. This high voltage is then pushed into the coil (phase 3). Finally, the energy in the coil is recovered back by switching the mosfet on again (bypassing body diode connection of the mosfet).
The transmitter coil is part of the flyback step-up converter.

Note:
The mosfet during recycling and charging phase is switched on and the phases 4+1 can be considered as a single TX pulse logic timing as these individual timings can be taken together.

This is the most power efficient solution ever. I would be quite surprized, if someone would come with a better solution.

Aziz

[Tepco]

What is shown in that post looks like class E amp/inverter stage, not even remotely similar to this by function or purpose.

[Aziz]

This one is much more efficient:

http://www.geotech1.com/forums/showpost.php?p=111998&postcount=819

(The post before and after might be interesting as well)

Up to 95% efficient (no bipolar transistors -> less losses).

One of the mature design solutions ever (not patentable).

It's interesting, that we are able to reinvent the wheel every day. Nevertheless, it's very funny to do it. (A la Obama: Yes, we can do it!).

Cheers,

Aziz

PS: It seems, I have missed some interesting discussions.