[Diy_efi] Inbuilt mosfet zener to clamp injectors

[Tony Bryant]

I'm having power dissapation problems with my LM1949-like injector driver 
circuit, notably in the zener.

I'm driving 3 injectors per channel, which judging by the 'scope traces are 
around 12mH each (Early '80s JECS/Nissan injectors).

What this means is the clamp zener has to suck around 9W  @ 7000RPM, which is 
getting to be quite a serious diode.  

My PCB has no means to take a TO-220 packaged zener that could take this load, 
but the drivers are 80V mosfets, which means if I simply throw away the zener 
and rely on the mosfet's inbuilt zener,  I transfer the 9W to the mosfet, 
which when added to it's 15W normal load, yields something it can deal with.

The question is:

How dodgy is it relying on the MOSFET's inbuilt zener? Am I asking for 
trouble?


_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi