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Subject: Re: How to drive a solenoid fuel injector?
Date: Sat, 21 Dec 2002 07:25:07 GMT
NNTP-Posting-Date: Sat, 21 Dec 2002 18:25:07 EST
Organization: BigPond Internet Services (http://www.bigpond.net.au)
In most of the ECU's I've designed I've driven the injector using the
lowest Rdson FET I could find, switching from the micro, via a series
resistor to the gate. This resistor plus Cgs filters the higher
frequencies, drastically reducing heating of the FET. Add a 24-28V zener
across source and drain. I used to use the IRF30N03. 30A continuous, at
30V in a DPAK. But have lately switched to much smaller SOT23 or SOT223
devices. Plenty of copper around D&S. You can hold in with a PWM signal
after initial switch on. This can be fixed time or by monitoring the
current in the source with a very low value resistor/amp.
Since this is a pin device (open/closed) you won't have much success, or
benefit from trying to control the valve position. This requires a
custom injector/solenoid, typically with a conical valve rather than a
"Christopher R. Carlen" wrote:
> Grog wrote:
> > How about something like this???
> > The LM1949 linear integrated circuit serves as an excellent control of fuel
> > injector drive circuitry in modern automotive systems.
> > The IC is designed to control an external power NPN Darlington transistor
> > that drives the high current injector solenoid.
> > The current required to open a solenoid is several times greater than the
> > current necessary to merely hold it open; therefore, the LM1949, by
> > directly sensing the actual solenoid current, initially saturates the driver until
> > the "peak" injector current is four times that of the idle or "holding" current.
> > http://www.national.com/pf/LM/LM1949.html
> Thanks for the info. Even if I don't use that thing, the datasheet made
> me realize more about how to do this than I knew before.
> I don't need a bipolar current source at all. Now I see what a zener
> diode is good for in clamping an inductor on flyback, it allows one to
> generate a faster di/dt when the drive is shut off compared to a plain
> diode clamp.
> Good day.
> Christopher R. Carlen
> Principal Laser/Optical Technologist
> Sandia National Laboratories CA USA
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