[Elecraft] HPS-1a Gamma Hybrid,Communications Power Supply

[David Cutter]

Paul

I'm always a little wary of this scheme since using it myself a while ago 
and not getting the results I expected.  I would call it a limiter not a 
crowbar.

I'm guessing these supplies have a relatively high (compared to conventional 
linear regulator) output resistance and when I've done this with other 
supplies it doesn't actually blow the fuse.  I'm sure it would still protect 
your rig, but simply act as a peak limiter using the fuse and holder and 
output resistance to pull the output below the clamping level.  Don't know 
what fuse you are using: say it's an ordinary "fast" blow 20A, then you will 
need >40A for 30s to blow it by which time the transient has long gone.  The 
clamping voltage also depends on the current drawn and could be as high as 
21.2V according to the spec. I would have to draw a load line to find out 
how that would perform with the supply but that would be only static 
conditions.

David
G3UNA

>

>
> I'm a bit leery of the over-voltage protection circuits built into these 
> small supplies.  I added a Vishay 1.5KE15A 15-volt transient suppressor, 
> reverse-based across the DC output (Mouser P/N 625-1.5KE15A).  The diode 
> is in parallel with the DC output terminals but a series fuse is inserted 
> just ahead of the diode.  This is essentially a zener crowbar device that 
> upon reaching 15 VDC will conduct and blow the DC fuse before any damage 
> is done to the rig (or one hopes!)
> >
> Paul, W9AC
> .
>