From: Jim Yanik
Subject: Re: SMPS Topology Question
Date: Fri, 15 Nov 2002 04:26:36 +0000 (UTC)
Organization: Friends of Lummox
References: <email@example.com> <7iJ7uRBnpA19EwBQ@jmwa.demon.co.uk>
NNTP-Posting-Date: Fri, 15 Nov 2002 04:26:36 +0000 (UTC)
John Woodgate wrote in
> I read in sci.electronics.design that james
> wrote (in <firstname.lastname@example.org>) about 'SMPS
> Topology Question', on Thu, 14 Nov 2002:
>>I'm thinking about designing an offline SMPS to supply a voltage of
>>400V at a peak current of 1A. This is for charging a large, high
>>voltage capacitor bank for use with linear magnetic accelerators
>>My question is: what topology to use?
>>Since we are talking a peak power of 400W, should i be thinking of a
>>forward converter or even half bridge or push pull?
>>Anyone have any views on this or know of any resoureces that may help
>>in this decision.
>>thanks in advance
> Forgive me, but I can't see why on earth you'd want to do that. Doesn't
> a coil gun operate just as a one-shot device? So you have a relatively
> LONG time to charge the cap. Even if you are on 120 V mains, a voltage-
> doubler rectifier will give you 340 V just from the filter cap. You can
> charge your big cap through a resistor at, say 100 mA or even less. It
> just takes longer to charge. If it's 1000 uF, then at 0.1 A constant
> current charge, it would take 340 x 0.001 = 0.34 coulomb to charge it,
> which 100 mA supplies in 3.4 seconds. Of course, the current won't be
> constant, but after 10 seconds the voltage will be within 5% of 340 V.
Actually for a coil gun,he's going to have to charge a cap for each coil
used.Meaning he's going to have to have a switching network to first charge
all the caps,then sequentially discharge each cap thru it's associated
coil.Coil guns use more than one coil to accellerate a projectile.
Jim Yanik,NRA member
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