[Diy_efi] Re: injector current-feedback driver

[Marcell Gal]

Hi Mark, 

> An HC device and a FET are the best combination to possibly make this work
> well.

Now I'm confused if HC output is sufficient or not.
Maybe it depends on the particular FET? 

> and will not have my data books handy. 

It's not urgent at all. 

> Have you considered using a comparator in place of Q feedback? I think you
> would get much more precise trigger level , 

yes, but a little variance (15%) after the current has run up
quickly does not hurt IMHO. I think to get much circuitry
(OPA, reference) to get 0.6 V drop (accross current measuring
resistor) down to 0.2 V is just superflouos. 

> Also, instead of an oscillating drive system to limit current, why not a
> definite cut back to a lower current? Seems simpler, but is this a heating
> problem?

I like to drive inductance this way. It is much more efficient,
longer life for the switching element, lower weight (of cooling).
I last did this with an npn transistor 10 years ago ;-), it
was a giant electromagnet there, it worked
fine but I understand a FET could be really better. 

Marcell

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