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rick-l rick-l is offline
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Join Date: May 2002
Location: St Louis
Posts: 4,213
Originally Posted by ischmitz View Post
Just an update from my recent work on a 911 DME:

Finally, a flyback stage takes care of the transients caused by switching off the inductive load.
Anyone notice the subtlety of what T404 driven off of pin 5 of the fuel injection controller ic along with D401, the 47 volt zener diode does?

When you are in hold mode T404 is on. It lets the current from the injector coil recirculate and maintains the energy stored in the magnetic field. If all you wanted to do was provide a path for the injector coil current a diode (like D1) would do that just fine.

When you want to collapse the magnetic field in the injector coil (to make it close quickly) you hold pin 1 at ground, leave T404 off, and the energy in the coil is dissipated in the zener @ 47V * I coil.

Think that is the way it works? I canít imagine any other reason for T404.
88 Cab
Old 03-31-2008, 02:56 PM
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