[Diy_efi] Flyback Diode (was 555 timer...)

[Daniel R. Nicoson]

Paul,

I am trying to learn more about using mosfets.  I have been tinkering with
other circuits besides the one I posted yesterday, some involve similar
inductive spikes, another circuit had even larger spikes than an injector
creates.  I have been using the 1N4003 diode across the mosfet to avoid
destruction.  I don't claim to have formal training in circuit design but am
having a blast working through my projects, trying to learn this stuff as I
go.

My question:

What specific item am I looking for in the datasheet to know that the
circuit won't need a flyback diode separate from what is internal to the
mosfet?

I looked in the datasheet for the IRF640.  It does have a section on
"Reverse Diode Limiting Values".  Which term is important here?

I have been using an N-Channel Power mosfet, RFP50N06, for some of my
projects.  With this mosfet I proved I have to use the external diode.  Its
data sheet does have a section titled "Source to Drain Diode
Specifications".  Some of the information is similar.

Thank you in advance for your help,

Dan Nicoson


> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]On
> Behalf Of Paul Bidmead
> Sent: Friday, July 08, 2005 12:15 AM
> To: diy_efi at diy-efi.org
> Subject: Re: [Diy_efi] 555 timer for injector driver
>
>
> the best injector driver i foun was an IRF640 FET it includes a flyback
> suppressor and can handle up to 200V/16A
>
> Kind Regards
> Paul Bidmead
> Design Engineer
> BidSpec
>
> ----- Original Message -----
> From: "Michael Richards" <michael at fastmail.ca>
> To: <diy_efi at diy-efi.org>
> Sent: Friday, July 08, 2005 12:15 AM
> Subject: RE: [Diy_efi] 555 timer for injector driver
>
>
> > Do not forget that you will need a flyback as well. Personally I find
> > it's far easier to just buy one of those expensive national
> > semiconductor injector driver chips and let it deal with the
> > requirements. This way you're not limited to saturated injectors
> > either.
> >
> > -Michael
> >
> >> I'd skip the solenoid to run your injector.  You're trying to control
> >> a slow device (injector) with possibly an even slower device
> >> (solenoid).
> >>
> >> Use either a Darlington transistor or a Mosfet as has already been
> >> suggested.  They are not too expensive from the local Radio Shack.  I
> >> use a good heat sink on the TIP-120 shown in the diagram.  When
> >> running at long pulse widths, it can build some heat.  (TIP-120 was
> >> used simply because it was in my parts bin, other Darlington's will
> >> work.  You would want to add few other things to use the Mosfet
> >> properly)
> >>
> >> I've attached a .pdf of the signal generator I've developed for use
> >> with my projects.  Use as much or as little of this circuit as you
> >> wish.  I'm only using a breadboard version at this point. I may make
> >> up a PCB later this month.
> >>
> >> Take care,
> >>
> >> Dan Nicoson
> >>
> >>
> >>> -----Original Message-----
> >>> From: diy_efi-bounces at diy-efi.org
> >>> [mailto:diy_efi-bounces at diy-efi.org]On Behalf Of jeff matthews
> >>> Sent: Wednesday, July 06, 2005 9:39 PM
> >>> To: diy_efi at diy-efi.org
> >>> Subject: [Diy_efi] 555 timer for injector driver
> >>>
> >>>
> >>> Hi-
> >>> To keep my ??? simple,  I built a 555 timer to work on a little
> >>> experiment,
> >>> I have it energizing the solenoid on a  12v relay, why won't it open
> >>> and close my injector? (it's just a basic saturated 550cc).  Is there
> >>> some secret to on making an injector operate?
> >>>
> >>> Like I stated,  this is for an experiment, just thought I could
> >>> handle making an injector fire on the bench...
> >>>
> >>> Best regards,
> >>> JEFF
> >>>
> >>>
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