I think they do, but only if the supply is putting out current to the load and
the current exceeds the value they've set for it. The crowbar firing definitely
exceeds the current limit but it's so sudden and complete that the design and
component values just cause the fuse to instantaneously blow.
Bob M.
======
--- On Wed, 12/24/08, Chuck Kelsey <wb2...@roadrunner.com> wrote:
> From: Chuck Kelsey <wb2...@roadrunner.com>
> Subject: Re: [Repeater-Builder] Re: Astron P/S question
> To: Repeater-Builder@yahoogroups.com
> Date: Wednesday, December 24, 2008, 12:59 PM
> I don't disagree with you, but it seems odd to me.
> Doesn't Astron use the
> current fold-back feature of the 723? If they do, it should
> just foldback
> due to overcurrent. If they don't, well, the fuse is
> the only salvation.
>
> Chuck
> WB2EDV
>
> ----- Original Message -----
> From: "wb6fly" <wb6...@verizon.net>
> To: <Repeater-Builder@yahoogroups.com>
> Sent: Wednesday, December 24, 2008 11:28 AM
> Subject: [Repeater-Builder] Re: Astron P/S question
>
> > Laryn,
> >
> > If the power supply were a switching design, current
> foldback would
> > occur. But, in the typical Astron RS-series linear
> supply, the
> > firing of the SCR puts a bolted short on the output.
> As soon as the
> > large capacitors on the output start to lose their
> charge, the
> > regulator tries to maintain the output voltage by
> turning on the pass
> > transistors to full conduction, quickly exceeding the
> current ratings
> > of the transformer and rectifier diodes and blowing
> the fuse. Every
> > time this has happened to an Astron RS supply (that I
> have personal
> > knowledge of), it has blown the fuse. Every time.
> Odd that your
> > experience is different. The fuse ratings are
> specified by Astron to
> > ensure that they will blow under such conditions.
> >
> > Because of their (RS-series) relative instability in
> high-RF
> > environments, I now install only Duracomm, Samlex, and
> Astron
> > switching power supplies. Lightweight, very
> efficient, and very
> > reliable. 'Nuff said.
> >
> > 73, Eric Lemmon WB6FLY
