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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: DC relay latching voltage
Date: Sat, 24 Aug 2024 23:22:01 -0700
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On 8/24/2024 11:21 PM, Don Y wrote:
> On 8/24/2024 10:03 PM, John Robertson wrote:
>> Good reading! It appears counterintuitive, but if I warp (!) my head around 
>> it I should be able to sort it out.
> 
> Think about the extremes:
> 
> - with NO diode  or snuber, there is nothing to keep the magnetic
>    field intact when the switch opens.  So, the spring force is the
>    sole actor in play, pulling the contacts open
> - with a diode, some current continues to "recirculate" in the coil
>    thus keeping the magnetic field active -- so it is trying to hold
>    the relay closed while the spring is trying to open it.  *When*
>    the recirculating current falls, the field collapses and the relay
>    can open.
> 
> The zener lets the circuit look more like the "no diode" case.

i.e., imagine that case as having an infinite voltage zener (open
circuit) in series with the diode -- NO diode!