Reply to "Weak DCS signals, Failed TIU Output Drivers, and Design Solutions devloped under collaboration between AGHR and MTH"

Barry Broskowitz posted:

Apparently Adrian's club did run in passive mode and still managed to cook TIU's.

I find myself scratching my head over this statement. My understanding is that a short circuit won't affect a TIU in Passive Mode. Is this not true for a current spike, as well?

It's not current that does the damage. It's the di/dt voltage. (here's a tutorial). The train is a motor (inductive). When the current jumps from the short, the 1st derivative, scaled by the inductance is developed across the rails.

An ideal short is a scaled step function Ks I(t)

where I(t) = 0 on the interval t<0,   I(t)=1 on the interval (t>0) and Ks is a scale for the current:

So the first derivative is the dirac (delta) function centered at t=0;

V(t) = d KsU(t)/dt

V(t) = Ks dirac(t)

The weight of the delta function voltage is Ks which is the peak voltage the TIU driver experiences. This is what the TVS is there to clamp.