Recycling TX power

[Tinkerer]

As you can see on the attached patent, 14 years ago the great metal detector designer Dave Johnson, invented a metal detector that recycled the TX power.

Technology has advanced a lot since then.

Can we, the "Consolidated Brain Power" of the forum improve on that design?

Are we capable of making use of the technological advances and design a detector that recycles the TX power and gives greater depth and sensitivity?

We might want to analyze first the patented design. Define it's advantages and it's shortcomings.

Was this design a commercial success? Why? or Why not?

Tinkerer

[Tepco]

First thing first,schematics:

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

[Aziz]

This one is much more efficient:
http://www.geotech1.com/forums/showp...&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.

[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]

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]

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]

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]

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

[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

[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

[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]

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/showp...7&postcount=32

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

Tinkerer

[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

[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.

[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