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Is this MOSFET driver circuit ok?

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langwadt:

--- Quote from: MagicSmoker on January 14, 2020, 12:37:33 pm ---
--- Quote from: langwadt on January 13, 2020, 11:19:02 pm ---...
or depending on the rating of the FET skip the zener and let the FET do the clamping

something like a VND7N04 has clamping and temperature/short circuit protection

--- End quote ---

I'd advise against this as not every FET is going to be happy with being repetitively avalanched, meaning a careless replacement could result in the immediate release of the precious magic smoke. Instead, replacing the freewheeling diode with a 24-36V bidirectional TVS* is a much safer alternative that will still achieve very speedy turn-off of the solenoid yet allow almost any MOSFET to be used in the circuit (well, any MOSFET with a Vds rating >50V or so, depending on what voltage the TVS clamps at, exactly).


* - e.g., SA24CA, SMAJ24CA, P6KE36CA, etc.

--- End quote ---

And if you carelessly replace parts with random parts that happens to have the same number of pins the circuit might not work ....


DBecker:

--- Quote from: MagicSmoker on January 14, 2020, 12:37:33 pm ---
--- Quote from: langwadt on January 13, 2020, 11:19:02 pm ---...
or depending on the rating of the FET skip the zener and let the FET do the clamping

something like a VND7N04 has clamping and temperature/short circuit protection

--- End quote ---

I'd advise against this as not every FET is going to be happy with being repetitively avalanched, meaning a careless replacement could result in the immediate release of the precious magic smoke.

--- End quote ---

A clamping driver, such as the OMNIFET parts mentioned above, does not use avalanche behavior.  It uses a zener diode from the drain to the gate.  This turns the MOSFET on to limit the inductive "kick" voltage.  It is more compact and effective than a traditional snubber circuit, and is much less sensitive to the load characteristics.

Chriss:
For sure guys I won't just pop out parts and replace them just so, I will check datasheets and infos about compatibility of the device and pinout arrangement etc.
But thanks for the precaution.

Reading your writings I slightly realized something what is maybe a better solution for my project than this what I built up and posted in my first post.

Maybe it is a better solution to avoid an active clamping circuit and using the avalanche behaviour of a proper mosfet.
I think from reading on the net and datasheets, to use the avalanche characteristic of a mosfet is more safer for the mosfet than to use an active clamping circuit.
From my perspective a mosfet which is suitable for driving inductive loads with internal protection etc. is a better option to use by me,
cos it is more precise calculated and built up compared to my calculations and maybe perspective of view.
Team of engineers done a much better protection and clamping for the specific mosfet than I can do as an average guy who has lot of electronics and programming knowledge but still not an official electronic engineer - part designer.

So, a mosfet let's say like the VND7N04 has a clamping circuit, a thermal and short protection circuit and a really dummi feedback but in conjunction with my dummy Attiny85 I could use that feedback to trigger an alarm and shut down immediately the circuit.

That sound so to me a more safer circuit than I did with all my mess of opto, clamping diode etc...

What do you think about this thinking path?
Maybe you can advice me a better or newer mosfet for my purpose?

btw. in what software was done that nice simulation what was posted by Zero999 ?

Thank you all of you for your time and help.
I learned lot of things from you.
My best regards.

MagicSmoker:

--- Quote from: DBecker on January 14, 2020, 05:53:55 pm ---A clamping driver, such as the OMNIFET parts mentioned above, does not use avalanche behavior.  It uses a zener diode from the drain to the gate.  This turns the MOSFET on to limit the inductive "kick" voltage.  It is more compact and effective than a traditional snubber circuit, and is much less sensitive to the load characteristics.

--- End quote ---

I didn't look up the datasheet for the above part, but my warning about not blithely relying on avalanching the mosfet with inductive loads applies to this as well: if a generic load switching circuit like this relies on a specific mosfet to not blow up then it's not a very robust design.



--- Quote from: Chriss on January 14, 2020, 07:56:59 pm ---...
Maybe it is a better solution to avoid an active clamping circuit and using the avalanche behaviour of a proper mosfet.
I think from reading on the net and datasheets, to use the avalanche characteristic of a mosfet is more safer for the mosfet than to use an active clamping circuit.
...

--- End quote ---

Erf, no, you got that backwards: only some MOSFETs are characterized for repetitive avalanche, and there are always strict limits on the amount of energy per avalanche regardless of whether it occurs regularly or just occasionally. My earlier suggestion to use a bidirectional TVS diode across the load (or the Zener across the MOSFET drain-source, as Zero999 shows) is the safest for both load and MOSFET, allows a wide variety of MOSFETs to be used, and enables much more rapid demagnetization of inductive loads than either a conventional freewheeling diode or the clever little MOSFET mentioned above that automatically turns itself back on when an inductive load "kicks" during turn-off.

P.S. - the simulation software Zero999 - and most of the rest of us here - use is LTspice


DBecker:

--- Quote from: MagicSmoker on January 14, 2020, 08:37:33 pm ---
--- Quote from: DBecker on January 14, 2020, 05:53:55 pm ---A clamping driver, such as the OMNIFET parts mentioned above, does not use avalanche behavior.  It uses a zener diode from the drain to the gate.  This turns the MOSFET on to limit the inductive "kick" voltage.  It is more compact and effective than a traditional snubber circuit, and is much less sensitive to the load characteristics.

--- End quote ---

I didn't look up the datasheet for the above part, but my warning about not blithely relying on avalanching the mosfet with inductive loads applies to this as well: if a generic load switching circuit like this relies on a specific mosfet to not blow up then it's not a very robust design.

--- End quote ---

It's a very robust design.  It's one of the standard ways to drive an injector.
A protected driver is not just a MOSFET, it has additional functions. You wouldn't expect to substitute a simple MOSFET in its place.

The trend is toward using larger chips with multiple drivers and integrated diagnostics, such as the TLE8888 or L9788.  They all use similar clamped drivers.  You don't see 1990s-style discrete solutions.

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