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winker · 12-03-2009, 05:32 PM

The 5.1v zeners across the injector and vss signals are doing nothing, assume they are to limit the input voltage to 5.1V. To work I believe they require at least 5mA before they will dump excess voltage across them.

The current circuit shows 100k resitors in series, so to get 5ma we would need a voltage of v=0.005x100000=500v (worst case in reality of a car is about 100v, but more likely 60-80v)!

Assume that the supply is 12v and the zener is a 5.1v.

We need to drop 6.9V (12-5.1) across the resistor @5mA (+a few uA for the load)

R=6.9/0.0051=1352, but recommend 1K or 1.2K (to be on safe side)

12-03-2009, 05:32 PM	#1 (permalink)
winker EcoModding Lurker Join Date: Nov 2009 Location: UK Posts: 18 Thanks: 0 Thanked 2 Times in 2 Posts	Protection Zeners The 5.1v zeners across the injector and vss signals are doing nothing, assume they are to limit the input voltage to 5.1V. To work I believe they require at least 5mA before they will dump excess voltage across them. The current circuit shows 100k resitors in series, so to get 5ma we would need a voltage of v=0.005x100000=500v (worst case in reality of a car is about 100v, but more likely 60-80v)! Assume that the supply is 12v and the zener is a 5.1v. We need to drop 6.9V (12-5.1) across the resistor @5mA (+a few uA for the load) R=6.9/0.0051=1352, but recommend 1K or 1.2K (to be on safe side) Last edited by dcb; 12-06-2009 at 12:02 PM..