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From: firstname.lastname@example.org (james)
Subject: Re: SMPS Topology Question
Date: 15 Nov 2002 03:41:26 -0800
References: <email@example.com> <7iJ7uRBnpA19EwBQ@jmwa.demon.co.uk>
NNTP-Posting-Date: 15 Nov 2002 11:41:26 GMT
Jim Yanik wrote in message news:...
> John Woodgate wrote in
> > >
> > 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.
I'm using one common capacitor bank for all of the coils in this
design. Instead of using SCRs to completely discharge caps (the common
method), I'm using banks of power MOSFETs allowing me to turn off the
coil at the optimal point.
When the coilgun is fired, the switches short out the cap bank. If the
capacitors are completely discharged, the power supply will try and
drive the very low impedance of the firing coils.
I'm thinking along the lines of either
-- disabling the power supply briefly whilst the coils are discharged
to prevent damage
-- relying on the maximum primary current limiting with a 384x control
-- implementing over current protection with a opto-isolated circuit
that shuts the 3842 down
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