Dave Zucal posted:SWISE asked if he read using PSX-AC's damage a TIU? I must have missed that in this long thread and really don't want to go back and read through it all. Can someone verify this ?
It's complicated but let me try to recap in a short post.
1. A PSX-AC protects circuits from over-current (melting down) but not transient over-voltage (being zapped).
2. This thread is about transient over-voltage causing the standard TVS inside the TIU to fail. The PSX-AC does not protect this. The transient over-voltages come from derailments and other ugly events. The result of the failure is reduced DCS excursion voltage on the digital square wave.
3. If you have inductive chokes between the power supply and layout to boost the thevnin impedance and improve the DCS signal, the abrupt current turn off when the PSX-AC trips causes a big di/dt voltage which can damage the standard TVS similar to a derailment. Again the result is reduced DCS excursion voltage.
In either case the standard TVS is not enough to absorb hits (at least in my club). We have modified the TIU with a different TVS and added silicon clamps, and now our club layout has not had a single channel degrade in almost a year since we started the work.
