MSD043A1XXV Panasonic AC Servo Driver 400w - MB3 connection help

[Doddy]

Fuse?, a transient voltage suppressor (TVS) is not intended to protect in the manner that he orchestrated.

The servo inputs, apart from the step/dir, are intended to be driven by the 12/24V supply to the servo driver, and through current sink inputs. The step/dir are intended for 5V differential, or single-ended supplies.

If you want to understand the difference - look at the resistors attached internal to the servo controller on page 11-13 of the manual - the step/dir are 270R (from memory), and the other inputs are 4.7k (4700R). Each opto-isolator device has an internal LED (the term opto-isolator is a bit confusing - they provide electrical isolation, by using an infra-red light between a LED and a photo-transistor across an air-gap, so the mechanism to drive this is to drive the LED 'on'). The LED will have, from memory, around 1.8V forward voltage drop. For the step/dir, 5v-1.8V = 3.2V. Through a 270R resistor, that's around 12mA (Ohm's Law: I=V/R). Typically drive current for a LED like this is around 10mA (max 20mA), the optical power is broadly proportional to the current - the choice of 270R is a standard value in the E3 etc range of resistor values - it's a "rule-of-thumb" resistor value). Now, the other inputs, with 4700R resistors - again, drop 1.8V across the LED, and if you're driving the stepper controller with 12V, then 12-1.8 = 10.2V, I = 10.2/4700 = 2mA, or at 24V then 24-1.8 = 22.2V, I = 22.2/4700 = 5mA. Actually, the currents a little low, but obviously it works - but hopefully you can see that if the 5V works on the Step/Dir at 12mA, that the other inputs with 4k7 resistors are perfectly safe at 24V because of the choice of resistors selected by the designer. being honest, I think the designer has been a little cautious.

Again, it's information provided by the manual that takes a bit of background knowledge/understanding to interpret properly.

But, yes, unduly worrying - the Step/Dir are designed for 5V signalling, the other controller inputs designated for current-sinking through a 4k7 resistor are designed for 12-24V signalling.