[ARC5] ARC5 CW Question

[mac via ARC5]

To speed up the release time add a resistor in series with the diode.   
Some
juggling here between release time and the size of the residual  
voltage spike that can
be accommodated by related circuitry.  Start off with around 500 ohms  
and
see what kind of a spike you get with a scope.  Also, make sure the  
diode is
wired in correctly -- the diode should be back-biased when the relay is
normally energized.   Might seem obvious but at work a number of years
ago we had a field technician decide that we engineers didn't
know what we were doing and  he Ignored our detailed instructions,  
wired all the
snubbing diodes included in a mod kit backwards and blew several power
supplies.

Dennis D. w7qho
Glendale, CA



****************


On Jun 22, 2014, at 4:50 PM, Dennis Monticelli wrote:

> When the current in the relay is suddenly interrupted it has to go
> somewhere; it cannot simply be "blocked."  The back EMF will soar as  
> high
> as it must to release it's stored energy in the form of a current  
> spike.
> That path will likely be a voltage breakdown somewhere within the  
> coil, or
> to the coil frame or via connected components.  Putting a reverse  
> diode
> defines the reverse current path to a very safe voltage level but as  
> was
> pointed out it takes longer for the energy to be released, which may  
> or may
> not be an issue depending upon the application.  One good way to  
> have your
> cake and eat it too is to define a reverse current path that is much
> greater than a diode drop.  For example, one could put a zener in  
> series
> with a diode across the coil.   When the diode conducts it does so  
> via the
> zener's voltage and then the relay's energy is released quickly and  
> safely.
>
> I usually just use a diode with relays, unless release speed is  
> important.
>
> Dennis AE6C
>