New PI technology proposals.

[Qiaozhi]

Hi Qiaozhi,
these parasitic effects are taken into account in the inductors model. You cannot see the values. Only the {LTX/4} is visible. There is {RTX/2} for LR and {CTX/2} for LC. Only parallel shunt resistance (G) is not taken into account (loss of inductor). This can be done, as I know this value exact.

Hi Aziz,

Please can you post here the coil subcircuit you are using?
Thanks.

[Aziz]

Hi 1843,

Hi Aziz,

I don't think the drain diode must be fast... a 1N400X can be used since never a reverse current flows through it.


Regards,
1843

a reverse current flows only when the flyback voltage exceeds the breakdown voltage specification. A typical reverse current on 1N400x is between 5 .. 50 µA and is depending on the temperature.
Generally it is important, that this blocking diode should have low reverse capacitance, low forward voltage drop, forward resistance and a high breakdown voltage.

High voltage rated diodes have typically high voltage drop. The higher the breakdown voltage, the lower the capacitance. But here is a drawback: some diodes are very temperature dependend.

BYV28-200 is a good one for replacing 1N400x.

Aziz

[Aziz]

Hi Qiaozhi,

Hi Aziz,

Please can you post here the coil subcircuit you are using?
Thanks.

here it comes.

To compare two different systems with same conditions (same exposed magnetic field energy), the coil current of the system 1 is 300 mA and of system 2 is 600 mA. It is the example of center-tapped coil configuration with splitted PI critical coil damping.
This example is not posted yet. So feel free to play with it.
The enclosed zip file is a .rar file. Remove .zip file extension before unpacking.

Aziz

[Aziz]

A special single ended version is also possible and omitting the need for differential signal front-end provided that the proposal works in real world (not only in the spice simulation ).
As you can see, there is huge signal quality available (surface area between two systems with equal exposed magnetic field energy and same targets). Also, provided that 1N4148 will survive high voltages. I will do some high voltage test's on 1N4148 today. If they won't survive, then other diodes must be used. If I don't reply, then probably i haven't survived the test due to high voltage shocks.

If offers 3 µs early sampling even the diodes are clamping on both systems. The RX voltage is stepped up like a Tesla coil. The high RX voltage is decoupled from the TX driver parts (diode, fet) and exceed the kV ranges easily.

Aziz

[Carl-NC]

Hi Carl,

There appears to be a small error here.

The lower inductance values are understandable, as the relationship between inductance and number of turns is not linear, but the resistance values must be wrong.

In the first example the 20 turns of 24AWG wire had a total resistance of 4 ohms, but the second example (which is essentially the same, just with a center-tap) only totals 2.2 ohms.

Yes, I noticed that. And my 4-tap coil has 5T coils with 0.42 ohms, for a total of 1.68 ohms. Don't know why.

- Carl

[UWLocator]

Yes, I noticed that. And my 4-tap coil has 5T coils with 0.42 ohms, for a total of 1.68 ohms. Don't know why.

- Carl

Does it show 1.68 ohms across the full coil on the 4-tap?

Rip

[Qiaozhi]

Does it show 1.68 ohms across the full coil on the 4-tap?

Rip

Good question.
I would expect it to measure the same as the untapped coil - same inductance, and same DC resistance.
Maybe Carl can recheck the measurements.

[Carl-NC]

Does it show 1.68 ohms across the full coil on the 4-tap?

3.6 ohms... but now I see why. I'm using a BK 878 RLC meter and the R setting apparently uses an AC signal as well, so inductance plays a role. It has settings for 120Hz and 1kHz, and when I switch to 120Hz the "resistance" drops to 1.5 ohms, which is about what my regular multimeter says.

- Carl

[UWLocator]

3.6 ohms... but now I see why. I'm using a BK 878 RLC meter and the R setting apparently uses an AC signal as well, so inductance plays a role. It has settings for 120Hz and 1kHz, and when I switch to 120Hz the "resistance" drops to 1.5 ohms, which is about what my regular multimeter says.

- Carl

That is why I still like the old Simpson 260. I know it uses DC only for resistance. I find even the cheap digital meters have a pulsed signal.

It also is much easier to see current swings on the needle.

Rip

[simonbaker]

breather summary

For those trying to follow this thread:

Is the following summary correct?

A) There are two main concepts being debated in this thread:

1. Whether distributed dissipation resistors (divide coil into sections and put parallel resistor across each section) in the TX coil cause faster decay of current and thus magnetic field during switch-off than a single resistor across entire coil.

2. Whether a center-tapped coil can be driven on one half but with damping resistors on both halves such that a higher total "flyback" voltage is achieved, which leads to faster damping of the coil current and magnetic field. Avoiding MOSFET breakdown is part of the goal (or maybe all of the goal).

3. A third side-issue is that center-tapped coil allows "differential" receive circuit which reduces noise and thus offers that benefit.

B) Carl did an experiment posted in the Coils section that "debunked" concept 1 -- dividing coil into four sections with separate resistors did not achieve faster decay. Therefore we are no longer discussing that design. Or is it still in play?

C) Aziz found errors in original assumptions about using center-tapped coil in concept 2, but it seems there is still some investigation that a center-tapped coil will allow higher "flyback" voltage and thus faster decay. There is a question as to whether effects of capacitance are being considered correctly.

Is this where we are? If not, where are we?

Regards,

-SB

[simonbaker]

analogy

I am wondering how center-tapped, half-driven TX coil is different from analogy with full transformer, like attached image (very simplified circuit)?

Forget about metal detectors -- could such a circuit achieve faster decay because of high voltage secondary? Or is there simply an impedance-matching effect where the secondary circuit resistor looks like R/100 to the primary circuit and circuit behaves same as if just primary with R/100 resistor?

-SB

[Qiaozhi]

Hi Qiaozhi,



here it comes.

To compare two different systems with same conditions (same exposed magnetic field energy), the coil current of the system 1 is 300 mA and of system 2 is 600 mA. It is the example of center-tapped coil configuration with splitted PI critical coil damping.
This example is not posted yet. So feel free to play with it.
The enclosed zip file is a .rar file. Remove .zip file extension before unpacking.

Aziz

Hi Aziz,

The rar file you attached only contains the BYV28 and IRF740 subcircuits. Do you have the subcircuit model for the coil?
You said earlier that you are not using the ideal inductor model. What model are you using?

[Aziz]

Hi Qiaozhi,

Hi Aziz,

The rar file you attached only contains the BYV28 and IRF740 subcircuits. Do you have the subcircuit model for the coil?
You said earlier that you are not using the ideal inductor model. What model are you using?

the .zip file is a .rar file (rename necessary). It contains 5 files. One of them should have the name TargetResponsebbct4splits.asc. (Just loaded and checked - no missing files there).
I am using the standard inductor model of LTspice IV. Filling then the parameters in the Dialogbox: Inductance, Series Resistance, Parallel Capacitance. This must be a liner inductor model.

Aziz

[Aziz]

Hi friends,

1N4148 diodes seems to accept high voltages without going out of order. I have roughly tested up to 800-1000 V with a series resistor of 6.8k.
Now the magnet wire is not convenient for such applications and found very interesting loadspeaker cables: tin plated stranded wires with insulation. I didn't find a thinner one and will look for the next time. There were a 4 mm^2 and 6mm^2 wires available and of course a little too thick for coils.

Aziz

PS: My test was using a switch with a 12 V power supply firing the coil up to 5 A and switching the switch 100-200 times on and off for different periods. Until I have new coils, I will make tests going into several kVolts.

[Qiaozhi]

Hi Qiaozhi,



the .zip file is a .rar file (rename necessary). It contains 5 files. One of them should have the name TargetResponsebbct4splits.asc. (Just loaded and checked - no missing files there).
I am using the standard inductor model of LTspice IV. Filling then the parameters in the Dialogbox: Inductance, Series Resistance, Parallel Capacitance. This must be a liner inductor model.

Aziz

Hi Aziz,

The problem is that I'm not using LTspice, so I don't have the inductor model. Examining the asc file with a text editor, tells me that L=300uH, C=100pF and R=2 ohms. I will use those values, unless you tell me otherwise.