[Diy_efi] 555 timer for injector driver

[Mike]

At 09:49 PM 7/11/05, you wrote:
>If the MOSFET is saturated time off or time on should not contribute to
>heat, only the number of transitions per second.  I sounds like your MOSFET
>is not saturated.  You need a logic MOSFET which will be saturated by a
>lower voltage on the gate.

Saturation isnt a term normally attributed to MOSFETs, "Rds on" is a more common
specifications assuming gate voltage is sufficient.. You *dont* necessarily need
a logic MOSFET unless your drive circuit definitely *wont* puncture the gate of
a MOSFET.  ie. If your gate drive cct produces 12v say for a MOSFET which
needs a 12v drive and you substitute a 5v or <cough> 3v FET then you face
the chance of destroying the gate before you make the first action.
In other words gates of MOSFETS have effective infinite impedance and are
easily destroyed by overvoltage - even a few volts above the recommended
ratings... As I've mentioned before watch out for parasitic oscillations and
check u have the correct gate resistor and a ferrite bead


"So better by far to understand instead of substitute"

sort of applies to the human race in general it seems

<chuckle>


Regards from


Mike Massen
Perth, Western Australia
VL Commodore Fuse Rail that wont warp or melt !
Twin Tyres etc
http://niche.iinet.net.au





>dh
>
>
>----- Original Message ----- 
>From: "Daniel R. Nicoson" <A6intruder at myo-p.com>
>To: <diy_efi at diy-efi.org>
>Sent: Thursday, July 07, 2005 11:02 AM
>Subject: RE: [Diy_efi] 555 timer for injector driver
>
>
>> Jeff,
>>
>> 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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>> > Diy_efi at diy-efi.org
>> > http://lists.diy-efi.org/mailman/listinfo/diy_efi
>> >
>>
>
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