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Why are IGBT's used in ignitions so much?

Started by Joerg April 28, 2018
Considering the typical saturation voltages of >1V it doesn't look 
attractive yet they are popular:

https://www.fairchildsemi.com/datasheets/FG/FGD3040G2_F085.pdf

Why?

There are plenty of cheap MOSFETs that are in the low tens of milliohms 
and thus show only a fraction of the losses while the coil current ramps 
up. You'd just have to add a zener from drain to gate in case the spark 
plug goes bad, the wire comes off or the controller lets the dwell time 
run out of hand. Plus some other gate protection but that's no problem.

-- 
Regards, Joerg

http://www.analogconsultants.com/
On Sat, 28 Apr 2018 13:23:20 -0700, Joerg <news@analogconsultants.com>
wrote:

>Considering the typical saturation voltages of >1V it doesn't look >attractive yet they are popular: > >https://www.fairchildsemi.com/datasheets/FG/FGD3040G2_F085.pdf > >Why? > >There are plenty of cheap MOSFETs that are in the low tens of milliohms >and thus show only a fraction of the losses while the coil current ramps >up. You'd just have to add a zener from drain to gate in case the spark >plug goes bad, the wire comes off or the controller lets the dwell time >run out of hand. Plus some other gate protection but that's no problem.
4V COLD Start requirement I'd guess. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Thinking outside the box... producing elegant solutions, by understanding what nature is hiding. "It is not in doing what you like, but in liking what you do that is the secret of happiness." -James Barrie
On Sat, 28 Apr 2018 13:23:20 -0700, Joerg <news@analogconsultants.com>
wrote:

>Considering the typical saturation voltages of >1V it doesn't look >attractive yet they are popular: > >https://www.fairchildsemi.com/datasheets/FG/FGD3040G2_F085.pdf > >Why? > >There are plenty of cheap MOSFETs that are in the low tens of milliohms >and thus show only a fraction of the losses while the coil current ramps >up. You'd just have to add a zener from drain to gate in case the spark >plug goes bad, the wire comes off or the controller lets the dwell time >run out of hand. Plus some other gate protection but that's no problem.
Probably small die = cheap. -- John Larkin Highland Technology, Inc lunatic fringe electronics
On 28/04/2018 21:50, Jim Thompson wrote:
> On Sat, 28 Apr 2018 13:23:20 -0700, Joerg <news@analogconsultants.com> > wrote: > >> Considering the typical saturation voltages of >1V it doesn't look >> attractive yet they are popular: >> >> https://www.fairchildsemi.com/datasheets/FG/FGD3040G2_F085.pdf >> >> Why? >> >> There are plenty of cheap MOSFETs that are in the low tens of milliohms >> and thus show only a fraction of the losses while the coil current ramps >> up. You'd just have to add a zener from drain to gate in case the spark >> plug goes bad, the wire comes off or the controller lets the dwell time >> run out of hand. Plus some other gate protection but that's no problem. > > 4V COLD Start requirement I'd guess.
But losing >1V from 4V makes it proportionately even worse? -- Mike Perkins Video Solutions Ltd www.videosolutions.ltd.uk
"Joerg" <news@analogconsultants.com> wrote in message 
news:fkk3gpFmm06U1@mid.individual.net...
> There are plenty of cheap MOSFETs that are in the low tens of milliohms > and thus show only a fraction of the losses while the coil current ramps > up.
At what Vds(max)? ;-) Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: https://www.seventransistorlabs.com/
On 2018-04-28 14:18, Mike Perkins wrote:
> On 28/04/2018 21:50, Jim Thompson wrote: >> On Sat, 28 Apr 2018 13:23:20 -0700, Joerg <news@analogconsultants.com> >> wrote: >> >>> Considering the typical saturation voltages of >1V it doesn't look >>> attractive yet they are popular: >>> >>> https://www.fairchildsemi.com/datasheets/FG/FGD3040G2_F085.pdf >>> >>> Why? >>> >>> There are plenty of cheap MOSFETs that are in the low tens of milliohms >>> and thus show only a fraction of the losses while the coil current ramps >>> up. You'd just have to add a zener from drain to gate in case the spark >>> plug goes bad, the wire comes off or the controller lets the dwell time >>> run out of hand. Plus some other gate protection but that's no problem. >> >> 4V COLD Start requirement I'd guess. >
That could be the reason though a gate voltage booster isn't that tricky.
> But losing >1V from 4V makes it proportionately even worse? >
It does, that would be a wimpy spark or no spark. -- Regards, Joerg http://www.analogconsultants.com/
On 2018-04-28 14:01, John Larkin wrote:
> On Sat, 28 Apr 2018 13:23:20 -0700, Joerg <news@analogconsultants.com> > wrote: > >> Considering the typical saturation voltages of >1V it doesn't look >> attractive yet they are popular: >> >> https://www.fairchildsemi.com/datasheets/FG/FGD3040G2_F085.pdf >> >> Why? >> >> There are plenty of cheap MOSFETs that are in the low tens of milliohms >> and thus show only a fraction of the losses while the coil current ramps >> up. You'd just have to add a zener from drain to gate in case the spark >> plug goes bad, the wire comes off or the controller lets the dwell time >> run out of hand. Plus some other gate protection but that's no problem. > > Probably small die = cheap. >
From what I have seen IGBT in similar power classes aren't smaller in the die than FETs. -- Regards, Joerg http://www.analogconsultants.com/
On 2018-04-28 15:16, Tim Williams wrote:
> "Joerg" <news@analogconsultants.com> wrote in message > news:fkk3gpFmm06U1@mid.individual.net... >> There are plenty of cheap MOSFETs that are in the low tens of >> milliohms and thus show only a fraction of the losses while the coil >> current ramps >> up. > > At what Vds(max)? ;-) >
You don't need much above 400V for an ignition. Easy to do with either kind. -- Regards, Joerg http://www.analogconsultants.com/
On Sun, 29 Apr 2018 09:52:21 -0700, Joerg <news@analogconsultants.com>
wrote:

>On 2018-04-28 15:16, Tim Williams wrote: >> "Joerg" <news@analogconsultants.com> wrote in message >> news:fkk3gpFmm06U1@mid.individual.net... >>> There are plenty of cheap MOSFETs that are in the low tens of >>> milliohms and thus show only a fraction of the losses while the coil >>> current ramps >>> up. >> >> At what Vds(max)? ;-) >> > >You don't need much above 400V for an ignition. Easy to do with either kind.
350V/5A is the general requirement, so I'd probably margin a wee-bit higher than 400V, maybe 600V. I don't think you can get NMOSPower like that with logic level gate voltages. Personally I've done it with Delco bipolar's where beta was only 3 at IC=5A ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Thinking outside the box... producing elegant solutions, by understanding what nature is hiding. "It is not in doing what you like, but in liking what you do that is the secret of happiness." -James Barrie
s&oslash;ndag den 29. april 2018 kl. 19.23.11 UTC+2 skrev Jim Thompson:
> On Sun, 29 Apr 2018 09:52:21 -0700, Joerg <news@analogconsultants.com> > wrote: > > >On 2018-04-28 15:16, Tim Williams wrote: > >> "Joerg" <news@analogconsultants.com> wrote in message > >> news:fkk3gpFmm06U1@mid.individual.net... > >>> There are plenty of cheap MOSFETs that are in the low tens of > >>> milliohms and thus show only a fraction of the losses while the coil > >>> current ramps > >>> up. > >> > >> At what Vds(max)? ;-) > >> > > > >You don't need much above 400V for an ignition. Easy to do with either kind. > > 350V/5A is the general requirement, so I'd probably margin a wee-bit > higher than 400V, maybe 600V.
most ignition igbt have an active clamp around 350-400V to protect the coil if there's a loose plug wire