Injectors and resistors (and i'm back)

[Sandy]

You don't need to waste the extra $$ on the FET drive, a TIP121 or better
(about 50 cents) will work great for peak and hold with that circuit. The
Flyback zener voltage is dependant on the decay time required for the
circuit, and that's why they just don't use a diode. I have used 33volt
zeners, and also tested with the easier to get Transient Voltage
Suppressors (TVS, like 1.5k33CA) that are easier to get in 5 watt ranges
from Digikey or Mouser. Both work great. Besure to heatsink the
transistor/FET when using Peak and Hold injectors, and lastly if you do
drive a FET or a IGBT, you will have to check the circuit for oscillations,
as I have built the driver with IGBT's and had to add a small capicator to
the Base of the IGBT to keep it stable.

Sandy

At 08:50 AM 11/24/98 -0600, you wrote:
>
>> > What about EMI when you shut off the inductive load... use the body
diode of
>> > the FET to catch the spike?... if so what voltage?  How about an RC
snubber
>> > across the injector... or is EMI not a problem (maybe inductance is low?)
>> 
>> Check out the schematics for using the Nat'l Semi LM1949 Inj Driver
>> Cntrlr. It's a PDF file available from www.nsc.com. It uses a 50V zener,
>> AIR..this for driving the std 4-1 peak and hold injector..ala GM TBI.
>
>They say you're losing your mind when you reply to yourself, but
>just to be clear...the spike is clipped by a 33v 5watt zener per
>LM1949 datasheet.                            **
>
>-greg
>