Electronic – Snubber on the line or just the inductor

snubbertransmission line

A document on the public internet, yet apparently covered by NDA, makes a surprising claim about snubbers. vendor link or archive.org

Page 12 shows a device powering and switching an inductive DC load.

similar to this.


simulate this circuit – Schematic created using CircuitLab

The text claims that the diode is more effective if located close to the load
(A) but how can that be? By putting is closer to the source (B) is also snubs the inductance of the cable connecting the source to the load.

So is there a reason to put the diode at the far end? (other than the likelihood that someone want to add an additional switch near the load (location C)

I built a similar circuit to what they described once and the diode near the load didn't offer sufficient snubbing to protect other electronics that was sharing the same cable. I had to put the diode at the relay end of the cable to get the electronics to survive the switching transients. I was using CAT-5e cable with two pairs for switched power and the other two pairs for power and data to the electronics.

Best Answer

This is what I found in the document that relates to your question: -

To minimize the antenna-like radiation of this electromagnetic energy from wires connected to the inductor, the flyback diode should be connected as physically close to the inductor as practicable. This approach also minimizes those parts of the circuit that are subject to an unwanted high-voltage.

And that is perfectly true (see page 6 of the first document).

On page 12 it says this: -

The recommended and most effective position for the diode is at the inductive load itself, if this is not possible the diode will still help suppress the voltage spike even if placed at the HID NAS product connector.

I do not see a contradiction here.