THE ELUSVE 1us TC TARGET

[Detectorist#1]

Hi Moodz,

It is interesting how external SiC 650V 4A (1.5V at 4A) diode will improve losses in comparison of internal diode in SiHB100N60E MOS FET with 1.2V max at 13A on internal diode. Who of two diodes will take the current?

[Detectorist#1]

According of graph from Tinkerer, switching losses in SiC diodes and Si pin diodes are remarkable different only at high frequencies (>100KHz). PI MD works at 10KHz max usually.

[moodz]

Hi Moodz,

It is interesting how external SiC 650V 4A (1.5V at 4A) diode will improve losses in comparison of internal diode in SiHB100N60E MOS FET with 1.2V max at 13A on internal diode. Who of two diodes will take the current?

Well for those two devices neither will work because the transmit cct flybacks for the CCPI ( AMX whatever ) will be 1200 volts so neither is suitable.

If you use the formula for calculating flybacks and want the square wave rise time to be say 1 microsecond ... 13 AMPS wont work because the flyback will be too high for that timing.

That device you found is interesting because it has a low forward voltage ... however it is unsuitable for the reasons above.

[moodz]

According of graph from Tinkerer, switching losses in SiC diodes and Si pin diodes are remarkable different only at high frequencies (>100KHz). PI MD works at 10KHz max usually.

Schottky diodes are not used because of switching speed losses ... they are used mainly because of the voltage drop across the diode is lower = less power loss.

[Detectorist#1]

Hi Moodz,
The same is the situation with 1200V working peek voltage:
-SiC diode IDM05G120C5 - 1200V 5A_ 1.5V at 5A
-MOS FET STW12N150K5 - 1500V 7A_ internal diode 1.5V max at 7A. If you use 1200V MOS FET, the voltage on internal diode will be lower.

[Detectorist#1]

The problem is that high voltage schottky diodes are only SiC technology. And this technology have voltage bigger than Si pin diodes

[moodz]

Hi Moodz,
The same is the situation with 1200V working peek voltage:
-SiC diode IDM05G120C5 - 1200V 5A_ 1.5V at 5A
-MOS FET STW12N150K5 - 1500V 7A_ internal diode 1.5V max at 7A. If you use 1200V MOS FET, the voltage on internal diode will be lower.

Listen mate ... anyone can google search and pick two examples to prove your point

HOWEVER

you need to read the datasheet properly ... that mosfet you picked has 1.5 ohm ON resistance ... so its not suitable ( as one of the CCPI circuits goals is efficiency )

and heres my quick google search VS-25ETS12S2LHM3 its 1.12 volts25 amps 1200 volts Schottky.
So that beats your mosfet diode LOL.

I never said you have to use a schottky ... I was only sharing what I use.

I would say that there will ALWAYS be an external schottky that you can find that will beat the body diode VD. ( if you look hard enough ).

[Detectorist#1]

Hi Moodz,
If you look hard enough, one fact have to be meted - this diode is for rectifiers on 50/60Hz. These diodes have very high capacitance and very low drop voltage.
The parameter - capacitance is NOT mentioned in datasheet. If 1N5408 diode (1000V 3A) have 30pF at 4V, for 25A diode with the same technology we have to expected app. 300pF at 4V.
For PI MD designs the total capacitance is important!

[Detectorist#1]

Also, the power diodes with this technology have very big reverse recovery time - tens of microseconds! This is not suitable for PI MD!

[moodz]

Hi Moodz,
If you look hard enough, one fact have to be meted - this diode is for rectifiers on 50/60Hz. These diodes have very high capacitance and very low drop voltage.
The parameter - capacitance is NOT mentioned in datasheet. If 1N5408 diode (1000V 3A) have 30pF at 4V, for 25A diode with the same technology we have to expected app. 300pF at 4V.
For PI MD designs the total capacitance is important!

Well I have an operational circuit and I actually add 470pF of capacitance across the coil to keep the flyback voltage below 1200 volts. ( in addition to the schottky diodes you are so concerned about )
The risetime is 0.89 microseconds ... so yes capacitance is important but you might do well to do some more research in this regard.


Additionally the reason they dont put reverse recovery times for SBDs in data sheets is because the recovery times are negligble.

As a side note your comments are not helpful to the progress of the AMX project since they dont advance the knowledge ... you are just confusing the readers trying to follow this thread.

[Tinkerer]

Detectorist#, thank you for the feedback.
I think it is 8 Mosfets or did I post a wrong schematic? Right, I just checked, it is a different schematic with 2 additional Mosfets. I will look for the right one.
2 high voltage Mosfets about US$ 10 each
6 Cheap low voltage Mosfets.

I would appreciate if you would tell me in more detail what your concerns are. Cost? Assembly? Timing?

Detectorist#,
By now you probably wonder if the Tinkerer TX is better. I don't know. Both have about the same function.
The Tinkerer TX is in its 5th generation. The Moodz TX is in the first generation. Time will tell which TX is the better one.

I looked at the board and the schematic posted above. This is the right schematic for the board.
It has 2 extra Mosfets that I have used to test ways to compensate the slope on the TX, caused by the losses of RX damping and large targets. The ground is a large target and when it is highly mineralized ground it is a very large target.
We have tested about 6 different ways to compensate for the TX slope, using this TX board.

Is this TX board perfect? No. It works as it is. It also could improved. The layout is not great. Smaller Mosfets could be used because the current never will exceed 1A. At the time I designed the board I was using higher Ampere currents.
There has been a considerable amount of evolution over the 5 generations. For Generation 6, I want to incorporate the improvements.

If you want, we can go over the schematic and look at the functions of each component.

I can post the Gerbers for this TX board if you want to order it. At JLC they cost about US$ 5 for 5 boards.

Or, we can jointly design the Gen 6 board. I am glad to accept all the help I can get.

[Detectorist#1]

Hi Moodz,

Yes, in datasheets of schottky diodes RRT is not mentioned, but VS-25ETS12S2LHM3 is NOT schottky! This is ordinary power Si diode for 50/60Hz rectifiers and these diodes have tens microseconds RRT.

[Detectorist#1]

Hi Tinkerer,

Thank you for well balanced answer. I will think for your proposal.

[moodz]

Hi Moodz,

Yes, in datasheets of schottky diodes RRT is not mentioned, but VS-25ETS12S2LHM3 is NOT schottky! This is ordinary power Si diode for 50/60Hz rectifiers and these diodes have tens microseconds RRT.

You are right ... it is incorrectly listed in my database as a schottky.
Never the less you have missed the main point about using a schottky in parallel with the mosfets and at this point I dont really care what your opinion is since you seem to like arguing for the sake of it.

[Detectorist#1]

Hi Moodz,
Don't be so angry! I understand well the idea of use external diode with lower VD for higher efficiency. All this is true when peek voltage is 1200V and the switching current is 1A.
The Sic transistor NTBG160N120SC1 (1200V 160mR) have VD of internal diode 3V at 1A current.
The SiC schottky diode IDM05G120C5 (1200V 5A) have VD 1.05V at 1A current. This is good primer for improved efficiency.
Go ahead in improving of AMX project!