@cnwdon posted:I think I've been missing something fundamental. The track voltage is nominally 19v or a bit less. The TVS and the beefy clamp can't be across that circuit pair with ~9v thresholds or they would be conducting and breaking down immediately given the peaks of the AC track voltage, wouldn't they?
You're indeed missing something. We're protecting the driver chips, but they're 5V parts! They don't connect directly to the track, there's a host of analog logic and a coupling transformer before the signal gets to the rails.
