Delta Pulse

[eclipse]

I made some tests today with 1x1 coil in air it detects shovel at 2 meters height in air on max depth settings, though max settings the detector is too noisy and i have to lower the settings when hunting.
Had troubles with unfinished coil - it short circuited and the was some smoke. After that the IRF was getting warm very quickly and no signal was heard. When the detector works with small coil enameled wire you can hear when the generator is working, there is some buzz noise, well after i smoked it there was no sound coming from the coil. I changed VD8, VD9, the IRF, LM556 and the detector worked again so if you have same problems you might want to try it.

[Attilawap]

Hy!
Can you tell me anybody what is a difference the Delta Pulse Sniffer XR71 between 2012.11.06 and 2014.03.09 versions? Which is a sensitivest?

[pigeon]

hi all
I have a delta pulse I use a coil 2m and 1m.
I when I detected with the coil I 2m she noise and when I am I want assurrer with the coil 1m it makes no noise.
I use the irfp460 or place of IRF840.
what is the problem?

thank you

[pigeon]

hi all

nobody has answer

[kt315]

this is last test I do before it will be shipping to mege. you are witnesses.

[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?

[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]

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]

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'?

[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

[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

[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?

[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.

[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

[greylourie]

Thanks for your example and explanation, Jose.