What is the purpose of the series diode?

[Teleno]

You may try - GB01SLT12-214 also 1.2KV,5p capacitance, less than 10ns , 10uA max leakage...only Power dissipation is 19W vs 64W.

This one has a lower forward voltage too. Thanks for the tip!

[Tinkerer]

It is also good to look at the capacitance x Voltage curve.

[kt315]

You may try - GB01SLT12-214 also 1.2KV,5p capacitance, less than 10ns , 10uA max leakage...only Power dissipation is 19W vs 64W.

it's 1 A. we need 10+ A.

[Teleno]

it's 1 A. we need 10+ A.

If you read the datasheet it can withstand 10 A pulsed.

[green]

The added diode allows earlier sampling. If pulsing 10A, don't need earlier sampling(don't want diode).

[kt315]

If you read the datasheet it can withstand 10 A pulsed.

stth1210 has 80 and 120 A pulsed. reading the datasheet.

[Teleno]

stth1210 has 80 and 120 A pulsed. reading the datasheet.

Certainly, and there are schottkys with similar ratings too. For example GC2X8MPS12-247
But I don't think the average detectorist here is designing electric cars.

[Qiaozhi]

Qiaozhi,

If you plan on writing another book, article, or forum thread on Geotech1, please consider doing a trade off analysis between these variables.
1. Coil inductance
2. Resonant frequency
3. Total capacitance as seen by the coil
4. Coax cable effect on capacitance seen by coil
5. Damping resistor value
6. Effect of damping resistor value on the coil discharge slope relative to fully stimulating a variety of target TCs
7. Delay necessary to detect a variety of low TC targets
8. Total power being used to make the TX pulse
9. Coil making techniques needed to work at low delays
10. Now the main point: The trade offs between the above issues to optimize response from various target sizes, shapes, metal type and TC.

If you did this you would synthesize a lot of Geotech1 forum content in one convenient place and help PI detector builders target their own detecting priorities.

Forum members, do you agree?

Thanks

Joseph J. Rogowski

This would be a complex task, but probably best carried out in a SPICE simulator.

[Carl-NC]

Qiaozhi,

If you plan on writing another book, article, or forum thread on Geotech1, please consider doing a trade off analysis between these variables.
1. Coil inductance
2. Resonant frequency
3. Total capacitance as seen by the coil
4. Coax cable effect on capacitance seen by coil
5. Damping resistor value
6. Effect of damping resistor value on the coil discharge slope relative to fully stimulating a variety of target TCs
7. Delay necessary to detect a variety of low TC targets
8. Total power being used to make the TX pulse
9. Coil making techniques needed to work at low delays
10. Now the main point: The trade offs between the above issues to optimize response from various target sizes, shapes, metal type and TC.

If you did this you would synthesize a lot of Geotech1 forum content in one convenient place and help PI detector builders target their own detecting priorities.

Forum members, do you agree?

Thanks

Joseph J. Rogowski

Items 2, 3, 4, 5, and 9 boil down to the same issue: minimize capacitance. Otherwise, most of this was being discussed in a thread ironically named "Optimizing Target Responses." As I am motivated (and as people ask questions) I will continue that thread.

[kt315]

Certainly, and there are schottkys with similar ratings too. For example GC2X8MPS12-247
But I don't think the average detectorist here is designing electric cars.

schottky has just one advantade - bit low direct voltage. but How Much low?
on just 1...1.2V. i do not see any advantage to use a schottky in this case.

[Teleno]

schottky has just one advantade - bit low direct voltage. but How Much low?
on just 1...1.2V. i do not see any advantage to use a schottky in this case.

The main advantage is zero reverse recovery time, as I explained.

Regular diodes conduct when reverse polarized for up to 1us. Fast recovery diodes from 50ns to 300ns.

The advantage in this case is a faster isolation of the MOSFET capacitance.

[kt315]

capacitance of a cable to coil is 200+pF and capacitance of winding. no sense.

[Teleno]

capacitance of a cable to coil is 200+pF and capacitance of winding. no sense.

MOSFET capacitance is 10 times that, so it makes lots of sense.

This is the voltage at the drain when the MOSFET capacitance is isolated by a Schottky diode:




Notice how the drain voltage starts decoupling from the coil voltage right at the peak, with no delay.

Instead, a fast diode still has a considerable delay, as the drain and coil voltages remain coupled for a while after the peak, the decoupling starting much later.

Fast recovery diode:

[kt315]

your screens are different scaled... i see 80ns at first and 40ns on second. is there a problem to show in one scale?

[Teleno]

your screens are different scaled... i see 80ns at first and 40ns on second. is there a problem to show in one scale?

Yes, there is the problem that I'm experimenting with different coils and circuits and I can't revert hardware changes just to make one point.

But it's the delay relative to the peak that's important, not the scale. The difference happens at any scale because the Schottky starts isolating the capacitance right at the peak, the PN-junction diodes don't.