Diode protection on relays.

I understand the reason why a diode is put across the actuator coil on a relay but ive seen what look like zener diodes on diagrams and puctures of relay boards. Am i seeing things or is there a reason fir using a zener?

I've not seen zener diodes used for that purpose. Can you post a link to an example?

Example? I have never seen a zener in that application either.

Ron

maybe im just thining that all zener diodes are those little glass bead type cases? are normal diodes also encased that way and that's what I've seen?

Maybe you saw a schottky diode symbol.

Diodes can be encapsulated in many types of material. glass, plastic etc.

https://www.google.co.uk/url?sa=i&url=http%3A%2F%2Fwww.picbasic.co.uk%2Fforum%2Fshowthread.php%3Ft%3D6784&psig=AOvVaw2Ll3E6d0jydoDDu7gU9FQe&ust=1588702734595000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCLCrz7zpmukCFQAAAAAdAAAAABAD

Now I see what you are getting at.

It’s not a standard relay but a single coil latching relay. Making IO A HIGH and IO B LOW will latch the relay. Making IO A LOW and IO B HIGH will unlatch the relay. So in a nutshell reversing coil polarity latches and unlatches the relay. So you won’t see a common diode used as a flyback diode but back to back zener diodes.

Ron

DKenp:
I understand the reason why a diode is put across the actuator coil on a relay but ive seen what look like zener diodes on diagrams and puctures of relay boards. Am i seeing things or is there a reason fir using a zener?

A zener + normal diode can be used to increase the speed the current drops. Effectively you make a diode
with a large forward voltage by placing zener and ordinary diodes in series, anode to anode. The normal diode
is in the same orientation as if it were the only free-wheel diode.

For inductors dI/dt = V/L, so to make the current drop more rapidly the voltage has to be larger. A simple diode
has only a small voltage of less than a volt of course.

The typical place this circuit is used is for high-speed solenoids where the device must recover quickly to be fired again, or to speed up the switch-off of a relay.

DKenp:
maybe im just thining that all zener diodes are those little glass bead type cases? are normal diodes also encased that way and that's what I've seen?

Diode package and diode type are not related like that. Package type is more related to power dissipation and max voltage (long bodied diodes). All semiconductor devices are small chips of silicon wafer on the inside.

DKenp:
maybe I'm just thinking that all Zener diodes are those little glass bead type cases? are normal diodes also encased that way and that's what I've seen?

Nowadays, the vast majority. :grinning:

Thanks folks.