Delta Pulse

[greylourie]

Cheers, Jose. For the images you posted, and commentary describing them.

[Jose]

Correct me if I'm wrong, in Limitador de Tension 2.JPG

R8 - 10K
R16 - 1R / 2watt
C3 - 4700uF/2x4700uF/10000uF 16V


The diode connected with the drain of the Mosfet can be 200V (example: BYV28-200- this is seen on PIM-2 schematic, also in SD2000),
though this is opposing of the suggested high voltage STTH1210 (1000V), perhaps this diode is not meant to limit voltage of the mosfet in the delta pulse unified.

The component values are correct.
As for diodes, the truth is that I'm using components recovered from old monitors.
When I see the values, I consult online, and you chose the highest tensions, and 3 ampere current .
I think it's wise to choose values greater than 500 volts, for DP.
Jose

[eclipse]

Hi Greylourie
The use of a series diode between the MOSFET and the coil continues to exist high voltages in the MOSFET, as can observed in "IMG 1" picture.
In "IMG 1" the limiter is disconnected. Each box represents 50V, the peak voltage, out of scale in ociloscopio.
In "IMG 2" with the limiter enabled, observed the peak voltage, is cut before reaching 400 volts.
In the "voltage limiter 2" scheme, is observed the point where the ociloscopio was connected, for measurements.
Jose
[ATTACH]33866[/ATTACH][ATTACH]33867[/ATTACH][ATTACH]33868[/ATTACH]

Correct me if I'm wrong, in Limitador de Tension 2.JPG

R8 - 10K
R16 - 1R / 2watt
C3 - 4700uF/2x4700uF/10000uF 16V


The diode connected with the drain of the Mosfet can be 200V (example: BYV28-200- this is seen on PIM-2 schematic, also in SD2000),
though this is opposing of the suggested high voltage STTH1210 (1000V), perhaps this diode is not meant to limit voltage of the mosfet in the delta pulse unified.

[Jose]

Hi Greylourie
The use of a series diode between the MOSFET and the coil continues to exist high voltages in the MOSFET, as can observed in "IMG 1" picture.
In "IMG 1" the limiter is disconnected. Each box represents 50V, the peak voltage, out of scale in ociloscopio.
In "IMG 2" with the limiter enabled, observed the peak voltage, is cut before reaching 400 volts.
In the "voltage limiter 2" scheme, is observed the point where the ociloscopio was connected, for measurements.
Jose

[greylourie]

It can be used in conjunction with the series diode between the MOSFET and the coil.
Even with the diode series, one can observe high voltages in the MOSFET, with ociloscopio.
In an experimental detector (not Delta Pulse), series and use diode voltage limiter to prevent noise generated by the zener protection in the IRF740.
Also decreases the heat generated in the MOSFET.
As I am using IRF740, R1, is set to cut approximately 380 volts.
As KT315 says, you can lose performance in some cases. You can always return to the source schema.
Jose

Jose, the high voltage across the mosfet ? Can you describe this more ?

[greylourie]

Thanks for your example and explanation, Jose.

[Jose]

It can be used in conjunction with the series diode between the MOSFET and the coil.
Even with the diode series, one can observe high voltages in the MOSFET, with ociloscopio.
In an experimental detector (not Delta Pulse), series and use diode voltage limiter to prevent noise generated by the zener protection in the IRF740.
Also decreases the heat generated in the MOSFET.
As I am using IRF740, R1, is set to cut approximately 380 volts.
As KT315 says, you can lose performance in some cases. You can always return to the source schema.
Jose

[kt315]

if you think/hope that snubber will give you effect low power then you deeply make mistake. the energy will also be spent, but not be on IRF but on the snubber resistor. advantage is only you can not set the radiator for IRF.

This transistor has rather high Rds 4-5 Ohms which I think is not wanted here. -- ha. you have to pay for HV exactly hight Rds. such technology and you do not get HV one with small Rds. this is why people use oldest IRF740 up to now.

[eclipse]

You can experiment with a voltage limiter as the diagram, I use one of my detectors.
You should set the value of R1 for pico, voltage value.
Check with a voltmeter at the end of R1.
Jose[ATTACH]33808[/ATTACH]

Thanks Jose, that's what exactly I had in mind!
I guess if someone doesn't have the high voltage diode STTH probably could use this instead. Not sure which is better/worse choice?

[eclipse]

I hope you will check DP with HV MOS-FET and show your results, something like http://www.st.com/web/en/resource/te...CD00050744.pdf
or what you intend speaking 'better one'?

This transistor has rather high Rds 4-5 Ohms which I think is not wanted here.
I'm thinking for a transistor having 0.2-0.3 Ohms Rds (On) 400-600V. Looking at catalogs seems ST have wider choice.

Examples:

FDP18N50

IRFB11N50APBF

IRFP450PBF

STP11NK50Z

STP11NM80

STP15NK50ZFP

[Jose]

You can experiment with a voltage limiter as the diagram, I use one of my detectors.
You should set the value of R1 for pico, voltage value.
Check with a voltmeter at the end of R1.
Jose

[kt315]

I hope you will check DP with HV MOS-FET and show your results, something like http://www.st.com/web/en/resource/te...CD00050744.pdf
or what you intend speaking 'better one'?

[eclipse]

for your mohandes..
1 ..The main difference is the DIODOS ultrafast (stth121od) So this elevates the voltage in approximately 200 voltage..

Okay the diode is already limiting the voltage at 200V, so no need to change anything there.
I will probably then need to get better transistor generating less heat if I want to use it on max pulse width.

[kt315]

high voltage diode in IRF line DRAIN in series pulls off this limitation 400V you so fear. seem you did not read all the thread you must and do not see a simple thing that DP is not needed in the snubber.

[eclipse]

If I was to use snubber circuit for the mosfet at what voltage should be the zener diode? I can hardy find zener in the range above 150V-180V.
I know all mosfets like the IRFs have built in zener protection but those work at 400V for IRF740 and 500V for the IRF840.

I did install good sized heatsink, coil resistance is ~2.8-3 ohms which should be sufficient.

I'm getting quite a bit heat on the transistor with big square coil and big pulse width (good stuff are deeper so..), I'm guessing the addon could help to limit the voltage peak
before the built-in protection kicks in, thus reduce the heat on the mosfet.
Resistance goes up with temperature so when the transistor gets a little bit heat Rds goes up, which triggers more heat trapping and so on.

I'm not sure what causes the heat by the way, could be just due to high current flowing through the transistor (in this case I could make the coil with higher resistance),
and not voltage peak?