High side switch.

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BeanieBots

Moderator
I was recently introduced to this
http://www.datasheetcatalog.org/datasheet/SGSThomsonMicroelectronics/mXywxyt.pdf
and thought of manie;)

It's designed for automotive use and as such is pretty much indestructible:cool:

It's rated at 5.5v to 36v with a current of 9A and Ron of 40mOhm.

I've put it through some tough tests and it's still living.

Switching inductive load 300mH @ 1A NO PROTECTION.
It's internal clamp clamps at 50v less than Vcc. Survived no problem but I'd suggest fitting a clamp diode anyway for inductive loads.

Switching a dead short from 36v. (no heatsink)
Internal current limit limits to about 18A.
Gets hot then thermally shuts down once case reaches ~130oC.

Also has significant ESD protection to 4kV.

The only downside is slow on/off times of 10's of microseconds so you won't be making any high efficiency switchers with it but at least it won't smoke if you try.

So far, the only way to kill it is to make Vcc > ~40v.

A challenge for you manie!
 
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BeanieBots

Moderator
Nothing about it's behaviour under severe abuse in the datasheet.
Is it just as indestructable? Have you tried to destroy it and failed like I have with the VN820?
 
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BeanieBots

Moderator
I'm sure there are countless versions with better charateristics, my point with this one is that it's tested to be manie proof:D (but not yet by manie)
 
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Dippy

Moderator
I'm sure we can all go through catalogues and find something a few milliohms or a few pennies less - it depends how much spare time you have.
Unless, by habit, you spend 3 hours a day sitting on the lavvy with a Farnell catalogue :)
Bit cold on the knees ain't it.

Eclectic has gone quiet - he must still be googling on the loo.
I think it was Andrew who said he absorbs all the catalogues, but he hasn't found a better option either....

BB's point was that he has given this device a real-world thrashing and concludes that it may be manie-proof... and THAT is the ultimate goal for semiconductor manufacturers . In fact, Microchip have a new App Note re testing standards ;)
 
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MartinM57

Moderator
eclectic said:
...recondite...
Click to expand...
Great word - I shall use it today in my day job...somehow:D

I retire from this thread - I use the device I mentioned, it works well for me in the design it is in...but I did bung a VN820 in last night's Farnell order to have a play with (wasn't £1.33 though :(). 40mohm is probably OK for me, and the bulletproofness is attractive for the monkeys that do the installations.

Thanks for the heads up BB - a worthwhile thread...
 
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BeanieBots

Moderator
Surely, anyone who knows the recondite word "recondite" and frequents an electronically and technically biased forum would also know about RDSon:confused:
I think EC is teasing us!
 
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manie

Senior Member
Thats the best NEW technology around ? Here is an OLD one, and it is "me" proof TOO !!
Costs a hell of a lot less, has Rds(on) 266.7 times lower (0.15mOhm), handles D-S 60V, handles Id 12A, Isc 27A and disipates 400W in Short Circuit, is thermally protected and switches off at 150 oC (then cools down and works again !). Now THIS IS A REAL COOL component.......... works for me.
 

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BeanieBots

Moderator
Nice device there manie.
So you couldn't blow it up!
I'll have a word with their marketing department, "tested by manie".
 
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manie

Senior Member
BB:
Well, in my "normal" ??? way of doing things, it has held up so far, did not even switch off under thermal overload yet, so must be good yes ??
 
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Dippy

Moderator
"did not even switch off under thermal overload yet, so must be good yes"

I've just done a circuit and fuse didn't blow - is that good?

Was it the cheapest one on Ebay manie ? :)

Is it a "High Sided Switch"?
Well, yes, it could be.
Or it could also be a Low Sided Switch.
It depends how you connect it into a circuit and drive it.
I wish I'd never heard of Vgs.

I was hoping that after all the months... the blood... the sweat.... and the tears.... that I, Beaniebots and a couple of others have spent on this subject that this would have been understood :(
I surrender.
 
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BCJKiwi

Senior Member
Well since the BTS112a is an N channel device and all the previous training you guys have worked so hard at has advised the NORMAL application of an N Channel device is as a low side switch (and a P channel for a high side) I felt it relevant to point out the original post specifically discussed a device that was promoted as a high side switch.

Was I really that wrong?
 
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manie

Senior Member
BCJ: Am using BTS112a in H-Bridge, N-channel only H-Bridge. No P-channels. That makes it a High-Side switch (two per bridge) does it not ?
 
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BeanieBots

Moderator
It certainly is much more common practice to use 'N' for low side and 'P' for high side.
Many struggle with the 'regular' drive methods but manie is now our resident FET expert so it's to be expected that he will adopt a less than conventional drive method to enhance his repetoire.;)

Don't forget, many designs found here are based on eBay's cheapest offerings and not electronic functionality:rolleyes:
(not that there's anything 'wrong' with using 'N' for high side switching)
 
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manie

Senior Member
Well, if its not "wrong", NOT FROM E_BAY !, and as stated by BB, "nice device...", then there is "no problem" ?:rolleyes:

Also, from what I have learnt (little...) and do understand (somewhat...), N-channels are just easier for me to work with. It also saved me some O/P pins on the Axe...

BCJ: Admittedly, I'm only switching lowish currents (1 - 1.5A) but the fact is I got it right, with Dippy et al's BLOOD, SWEAT and TEARS......;)

On a serious note, this device survived 10A loads in a previous project where some IRF's failed (albeit on LOW side...)
 
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brucewebb404

New Member
OK - Now what?

So, does anyone have a simple solution for high-side control in an automotive environment?

The project uses an 18X to control six 12V bulbs/LED packages. The bulbs/LEDS are 'normal' automotive bulbs with multiple filaments and a common ground (earth) connection - so I don't want to use an N-channel MOSFET in low-side mode. The first prototype used relays driven by transistors, but that seems too clunky and probably would be unreliable in the long run.

Now, I am considering a P-channel MOSFETs driven directly by the PICAXE or by a ULN2803 that is on the PIXAXE project board.

This has obviously been done a million times, so there is no reason for me to reinvent the wheel!
 
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BCJKiwi

Senior Member
Use the part BB suggested in Post # 1 or the similar VN05N-E which is available from RS (and others).

These are specifically designed for Automotive use with a recommended application of the VN05N-E being for light assemblies.

The VN05N-E has all the driver circuits and protection required to run straight off the Picaxe output - just use a limiting resistor in the control line to limit the current.
 
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BeanieBots

Moderator
The VN820 which I suggested is probably your best bet. It also has a logic output which will indicate if the load is missing (blown bulb).
As for reliability, correctly rated relays are very reliable, especially in an automotive environment which is very demanding on ANY silicon solution. That's why they are still largely used in such environments and many safety circuits in preference to solid state solutions. Often cheaper too.
 
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brucewebb404

New Member
True enough, but I would still prefer to keep a flasher circuit (my application) electronic rather than electromechanical.

The suggested parts have been a little hard to find - especially in a through-hole (easiest to prototype) version.
 
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