[Diy_efi] Driving injector: forward biased diode between B and C of NPN

[944Technologist]

It sounds like the same circuit used in the ML4.1 (copy of pdf sent to you
direct).

FR Wilk
____________________________________

----- Original Message -----
From: "Stephen Webb" <swebb at netlab.uky.edu>
To: <diy_efi at diy-efi.org>
Sent: Sunday, August 04, 2002 10:55 PM
Subject: [Diy_efi] Driving injector: forward biased diode between B and C of
NPN


>
> I'm getting my hands a bit dirty trying to reverse-engineer an injector
> driver circuit.  The box is actually a K-jetronic control unit from a VW
> which drives a "frequency valve", which is more or less a fuel injector.
>
> One side of the injector is always hot, the other side is switched with
> what appears to be an NPN transistor, though I could be wrong on that
> (couldn't find a listing for the part numbers)  The markings are:
>
> PH ON588  m8827
>
> For now I am going to assume it's an NPN transistor.  Everything about how
> it's connected makes sense to me except for a diode which is connected
> from the base to the collector.
>
> Could someone explain what this diode does?
>
> I'm stepping outside of my normal area of expertise on this, so if this is
> basic stuff, I apologize.  From reading TAOE I gather that a reverse
> biased diode across an inductive load may be expected (there isn't one,
> though there is a 10 ohm, 10 watt+ resistor in series).  Also there is
> mention of a base-emitter diode, but I haven't been able to find anything
> on a base-collector diode.
>
>
> TIA
>
> -Steve
>
>
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