[Diy_efi] injector current-feedback driver

[Marcell Gal]

Hello guys, 

Mark Bowers & Family writes:
> The heat generated in the drive devices should also be lower, as the drive
> currents are lower for high Z injectors.

Are there people using feedback-ed injector current limiting setups?
It seems * most popular setups are:
 - user specified PWM limiting without feedback (megasquirt?)
 - no current limit 

The current limiting can be quite simple, and
the ECU can have diagnosis data about proper (or electrically failed)
injector operation. 

http://x-dsl.hu/genboard/injector/injdrive.pdf
(the geda .sch and .ps is also there)
The circuit works by masking the master injection signal
when injector current exceeds a threshold. It has a histeresis
comparator. The histeresis can be set with Rhisteresis.
The frequency will not be very stable.
The limiting current is basically wired in by Rcurrent (so
that voltage drop is ~0.7V), but you do not want to change
that except when also changing the injector.
Do you have comments on the circuit? 

Does the FCC come after me if I do not use  a
fixed-freq PWM limiting (SGS3524 ?) but simple histeresis comparator
like above? 

This circuit relieves the ECU from high freq switching
of injector signals (eg. from software) for current-limiting
which is nice if you drive many sequential
injectors and your particular uC does not have enough hardware PWM outputs. 

Can 4 paralleled HC7404 inverters drive an injector driving
NPN transistor? 

Why is it a problem, if injector turnoff is slow?
(eg 2 V = -L di/dt). I need to drive the injector with a
shorter signal, then, right? Isn't turnoff deterministic enough? 

thanx:
Marcell 

* btw. schematic links on    
http://www.diy-efi.org/efi332/hardware/hardware.htm
are broken: point to ....com insted of .org 

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