AMX TX

[Willy Bayot]

Did you post something about this before? I've poked around various threads but can't find anything.

Then, after solving the precise measurement of the ramp of current, we should also solve how to apply the corrections!!!

[Willy Bayot]

This feature has suddenly appeared in this project even if it was already discussed in details elsewhere in the forum.
I think we should first list the benefits we expect from this new TX approach compared to the traditional unipolar TX for PI systems.
I can list them as far as I understand the details (to be commented and possibly completed and/or corrected):

1. Intrinsically BIPOLAR (gets rid of the Earth Magnetic Field effects)
2. Low Energy requirement from Battery --> Most of the energy injected in coil is recycled on consecutive pulse periods . The only energy losses are due to resistive coil circuits (constant) and to the absorption by ground and targets (highly variable). There is no need of damping the TX circuit. Note : Traditional PI's loose all energy injected in coil at end of each pulse period through the DAMPING --> Traditional PI's are large consumers of battery energy and generate a lot of heat inside the box)
3. No detrimental (negative) Eddy Currents generated during the long growing phase of the coil current (CONSTANT CURRENT vs sawtooth-shaped current). Targets with TC longer than the pulse half-period can still generate those.
4. Internal capacitance of the coil is not an obstacle to low pulse delays as in traditional PI's. Thus, higher inductance coils (more turns and lower current) is a possible option. Less coil current-->simpler Power supplies, lower cable and coil wire diameter, higher amp/turn. BUT Higher flyback--> needs the most modern MOSFET's with high VDS and low RdsON, 1200V, 60mOhm are widely available now
5. Only slightly more complex TX circuit than traditional single MOSFET.

PROBLEM TO BE SOLVED: Needs compensation of energy losses to guarantee the constant current. Question is: How do we compensate the constant and variable energy losses?

6. Traditional PI's generate an effective action on the targets during the second half of each period, the first half being the building-up of the ramp of coil current. This approach (Constant Current or Square current wave) generates a variable magnetic field and eddy currents during EACH half period. For the same value of KPPS, we get twice the decay slopes.
7. No need for heatsink over the damping resistor since there is NO damping resistor at the XMIT level. No heatssink over the MOSFET's if low RdsON.

Condtions under which this circuit should work:

1. All MOSFET's should be selected for a MINIMAL RDsON
2. The two main switching MOSFET (on both sides of the coil) should be selected with a MAXIMUM VDS to sustain the high flyback voltage without avalanching. The other MOSFET's can be low volatae type.
3. The small capacitor making the resonant circuit with the inductance of the coil should also be of high voltage type.
4. The two triggering signals should be strictly complementary and preferably generated both by hardware and not complemented by software (if both ON at the same time--> BOOUM)
5. The two triggering signals should have a dead time at each side. The dead time duration should be set depending on the switching speed of the main MOSFET's

[Willy Bayot]

I've actually used a 0.033 ohm in the supply line to the high side switches and a 100x current sense amp IC (INA293B3-Q1) for the exact same purpose. I try to minimize any additional resistance in the low side

I am afraid that this (obvious and direct) method will not give enough precision when measured in the XMIT circuit. It also risks to disturb the XMIT pulses.
I woud suggest to make measurements at the RECEIVER level instead.

[Carl-NC]

I've actually used a 0.033 ohm in the supply line to the high side switches and a 100x current sense amp IC (INA293B3-Q1) for the exact same purpose. I try to minimize any additional resistance in the low side

Did you post something about this before? I've poked around various threads but can't find anything.

[KingJL]

... I imagine we will need to add a current-monitoring resistor to the low-side switches and use it to control the TX power supply. Haven't given this much thought.

I've actually used a 0.033 ohm in the supply line to the high side switches and a 100x current sense amp IC (INA293B3-Q1) for the exact same purpose. I try to minimize any additional resistance in the low side

[Carl-NC]

1. Intrinsically BIPOLAR (gets rid of the Earth Magnetic Field effects)

IMO the definition should be for bipolar, no matter what kind of bipolar. Otherwise you are limited in pulse rate to 5-10kHz with a lot of wasted time.

2. Low Energy requirement from Battery --> Most of the energy injected in coil is recycled on consecutive pulse periods . The only energy losses are due to resistive coil circuits (constant) and to the absorption by ground and targets (highly variable). There is no need of damping the TX circuit. Note : Traditional PI's loose all energy injected in coil at end of each pulse period through the DAMPING --> Traditional PI's are large consumers of battery energy and generate a lot of heat inside the box)

The only energy that gets recycled is the turn-off flyback which is immediately recycled in the turn-on fly-forward. In between the transitions, the DC current through the coil is an all-loss current. However, that current is supplied by, say, a 1.5V supply instead of a 12V supply. And the huge benefit is it's fairly constant vs pulse rate.

As an example, if you take a TDI-like TX of 100us, a ramped peak current of 2A, supply=12V, and a rep rate of 320us then the power consumption is 3.75W. If you take the CCPI circuit, then for the same 2A but at 1.5V, the power is 3W. Assuming the transitions lose no power (but they do) this will be constant for 1kHz or 50kHz.

3. No detrimental (negative) Eddy Currents generated during the long growing phase of the coil current (CONSTANT CURRENT vs sawtooth-shaped current). Targets with TC longer than the pulse half-period can still generate those.

Yep.

4. Internal capacitance of the coil is not an obstacle to low pulse delays as in traditional PI's. Thus, higher inductance coils (more turns and lower current) is a possible option. Less coil current-->simpler Power supplies, lower cable and coil wire diameter, higher amp/turn. BUT Higher flyback--> needs the most modern MOSFET's with high VDS and low RdsON, 1200V, 60mOhm are widely available now

This where the above power argument can take a right turn. Instead of 2A through a 24T coil, you push 1A through a 48T coil. Now that 3W drops to 1.5W. I like it! However, that 48T coil needs to have wire with 1.4x the diameter, meaning the weight goes up by 4x. There may be particular advantages in different coils of different inductances so you can probably accept a wide variety of turns, with accompanying trade-offs.

5. Only slightly more complex TX circuit than traditional single MOSFET.[/LIST]PROBLEM TO BE SOLVED: Needs compensation of energy losses to guarantee the constant current. Question is: How do we compensate the constant and variable energy losses?

I imagine we will need to add a current-monitoring resistor to the low-side switches and use it to control the TX power supply. Haven't given this much thought.

[Carl-NC]

It's a little stupid to go to the other from one topic to collect data .. I guess everything should be in one topic.For TX I go to one topic for RX to another topic for PCB on the third topic

I find it a bit refreshing that we don't have a dozen different discussions all in one thread, where later it is hopeless to follow what was said.

[Willy Bayot]

In 3 months of actually using the CC TX board, I have never experienced any significant energy loss needing compensation ( except when I increased the TX current such that the flyback exceeded the MOSFET breakdown voltage... that affects more than just energy loss ). Have been using it with SuperD (315 uH, 0.6 ohm TX coil) and a Concentric (500 uH, 1.5 ohm TX coil). One thing to mention about CC is energy losses due to higher resistance TX coils... I see degradation when coils get into the 4 ohm and greater range. And you need to be very selective in the selection of the MOSFETs (both LV and HV) to keep "LOW" RDS on (and should not introduce any additional resistance in the source to GND circuit of the 2 LV MOSFETs).

We have personally experienced FAST variations of energy absorption (and subsequent variations of current slope and signal offfset) coming from slight variations of coil height over ground during a swing.
Laboratory testings do not show this.

However, our coils were in the mH range and not in the µH range!! This could possibly explain that.

[KingJL]

[/LIST]PROBLEM TO BE SOLVED: Needs compensation of energy losses to guarantee the constant current. Question is: How do we compensate the constant and variable energy losses?

In 3 months of actually using the CC TX board, I have never experienced any significant energy loss needing compensation ( except when I increased the TX current such that the flyback exceeded the MOSFET breakdown voltage... that affects more than just energy loss ). Have been using it with SuperD (315 uH, 0.6 ohm TX coil) and a Concentric (500 uH, 1.5 ohm TX coil). One thing to mention about CC is energy losses due to higher resistance TX coils... I see degradation when coils get into the 4 ohm and greater range. And you need to be very selective in the selection of the MOSFETs (both LV and HV) to keep "LOW" RDS on (and should not introduce any additional resistance in the source to GND circuit of the 2 LV MOSFETs).

[ivconic]

It's a little stupid to go to the other from one topic to collect data .. I guess everything should be in one topic.For TX I go to one topic for RX to another topic for PCB on the third topic

[Orbit]

It's a little stupid to go to the other from one topic to collect data .. I guess everything should be in one topic.For TX I go to one topic for RX to another topic for PCB on the third topic

[Willy Bayot]

For the initial TX module I propose to use the schematic and PCB here https://www.geotech1.com/forums/foru...376#post408376

and here https://www.geotech1.com/forums/foru...491#post408491

Thank you KingJL

A working LTSpice simulation is included.

For engineers who are familiar with traditional PI, I recommend to play some with the simulation as it is quite different from traditional PI.

Please comment. We are keen to hear opinions.

This feature has suddenly appeared in this project even if it was already discussed in details elsewhere in the forum.
I think we should first list the benefits we expect from this new TX approach compared to the traditional unipolar TX for PI systems.
I can list them as far as I understand the details (to be commented and possibly completed and/or corrected):

1. Intrinsically BIPOLAR (gets rid of the Earth Magnetic Field effects)
2. Low Energy requirement from Battery --> Most of the energy injected in coil is recycled on consecutive pulse periods . The only energy losses are due to resistive coil circuits (constant) and to the absorption by ground and targets (highly variable). There is no need of damping the TX circuit. Note : Traditional PI's loose all energy injected in coil at end of each pulse period through the DAMPING --> Traditional PI's are large consumers of battery energy and generate a lot of heat inside the box)
3. No detrimental (negative) Eddy Currents generated during the long growing phase of the coil current (CONSTANT CURRENT vs sawtooth-shaped current). Targets with TC longer than the pulse half-period can still generate those.
4. Internal capacitance of the coil is not an obstacle to low pulse delays as in traditional PI's. Thus, higher inductance coils (more turns and lower current) is a possible option. Less coil current-->simpler Power supplies, lower cable and coil wire diameter, higher amp/turn. BUT Higher flyback--> needs the most modern MOSFET's with high VDS and low RdsON, 1200V, 60mOhm are widely available now
5. Only slightly more complex TX circuit than traditional single MOSFET.

PROBLEM TO BE SOLVED: Needs compensation of energy losses to guarantee the constant current. Question is: How do we compensate the constant and variable energy losses?

[KingJL]

https://www.geotech1.com/forums/forum/projects/differential-front-end-pi/408045-bipolar-alternative-to-h-bridge-generating-sine-waveforms-half-single-full?p=408145#post408145

Schematic and Gerber files. KingJL even offered ready made PCB's.

Actually, I would recommend the schematic and Gerbers of post #16 of the referenced thread as the schematic and Gerbers were updated to accommodate on board selection of CC and half-sine operating modes.

[Tinkerer]

Which one exactly?
I searched whole topic from the link, I see several attempts in spice. Also I see changes. But I don't see final schematic done in any conventional software.
You don't expect one to use spice scribbles as serious schematic?
Anyone shall post complete final schematic HERE, done in any conventional schematic layout software, same applies for pcb.
...
Sorry to say; but this project will soon move to the "failed and unfinished projects" section. Because there are too many empty stories and "zero" concrete works.
And I'll say it again; do any of you have anything practical to show from the works? Video? Youtube is free for use, in case you didn't know.
Idle trumpeting and playing spice video games... that's not a serious approach.

https://www.geotech1.com/forums/forum/projects/differential-front-end-pi/408045-bipolar-alternative-to-h-bridge-generating-sine-waveforms-half-single-full?p=408145#post408145

Schematic and Gerber files. KingJL even offered ready made PCB's.

[Willy Bayot]

Which one exactly?
I searched whole topic from the link, I see several attempts in spice. Also I see changes. But I don't see final schematic done in any conventional software.
You don't expect one to use spice scribbles as serious schematic?
Anyone shall post complete final schematic HERE, done in any conventional schematic layout software, same applies for pcb.
...
Sorry to say; but this project will soon move to the "failed and unfinished projects" section. Because there are too many empty stories and "zero" concrete works.
And I'll say it again; do any of you have anything practical to show from the works? Video? Youtube is free for use, in case you didn't know.
Idle trumpeting and playing spice video games... that's not a serious approach.

I think you have not searched long enough.

That one is the original schematic:

https://www.geotech1.com/forums/filedata/fetch?id=408190

This the posts:

https://www.geotech1.com/forums/forum/projects/differential-front-end-pi/408045-bipolar-alternative-to-h-bridge-generating-sine-waveforms-half-single-full/page3#post408376

He even gave the BOM and the GERBER files ( in posts #16 and #17) if you are interested to make that PCB yourself

It seems that you largely downplay the importance of simulating electronic circuits before implementing them.
This design process is very important even if we know very well that a real implementation could have slightly different behaviours than the simulations.
SPICE simulators have made a lot of progress nowadays, we have plenty of experiences showing that they represent a good result approximation of a circuit if the component models are correct.

What do you expect from this whole exercise (project)?
Did you expect that you would get on your table the dinner already seasoned and hot from the oven?
No, if we make that exercise, it is because there are still a LOT of unknown in the PI technologies and we assume that a team made of a mix of specialties and experiences could help making a few progress for the good of all participants.
The best way to start up this exercise was to give a real requirement document. That's what Tony has done.
Let's all play the game.
We must accept that the trip is still long before getting to the end results!!!