[Diy_efi] LM1949 peak-hold driver chip , bank fire 4 injectors?

[Tony Bryant]

On Wed, 11 Sep 2002 06:51, Les Dittert wrote:
> The national LM1949 is made to drive a transistor to fire an
> injector peak and hold style. Can someone tell me to tell me if
> it's possible to use this with a bank firing of 4  injectors?
> My concern is the selection of the proper transistor (can it be a
> mosfet)
> and also the overloading of the zenor diode, since it's getting back
> current
>  from 4 injectors instead of one.

I think its fine, if the injectors are of similar inductance, since the 
current in the peak phase through will ramp up independantly and a rate
inversely proportional to the inductance

The zener takes the whole of the energy stored into the inductors, so size it 
using:

E= (LI^2)/2
Pzener= fmax(LI^2)/2

The mosfet passes the average current:

Pmosfet=(Iavg^2)Rds

Iavg ~=~ Ihold * Duty

The stablility of the hold feedback loop is up for question though - any body?


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