[Diy_efi] Driving injector: forward biased diode between B

[Mike]

Two possibles

a.	If there is no diode across the coil of the injector
	then its to protect the base-collector junction of
	the npn from back emf from the coil.
b.	Some earlier npn transistors turn off time was reduced
	if a schottky diode was connected as you have observed.

rgds

mike

At 01:55 AM 5/8/2002 -0400, you wrote:
>
>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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