From: email@example.com (Nico Coesel)
Subject: Re: SMPS Topology Question
Date: Fri, 15 Nov 2002 12:53:44 GMT
References: <firstname.lastname@example.org> <7iJ7uRBnpA19EwBQ@jmwa.demon.co.uk> <email@example.com>
NNTP-Posting-Date: 15 Nov 2002 12:54:58 GMT
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firstname.lastname@example.org (james) wrote:
>John Woodgate wrote in message news:<7iJ7uRBnpA19EwBQ@jmwa.demon.co.uk>...
>> I read in sci.electronics.design that james
>> wrote (in <email@example.com>) 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?
>> >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.
>I appreciate what you are saying, but this is the prototype idea for a
>multistage, rapid firing coilgun. This will require rapid charging of
>the capacitor banks. My current cap bank size is 6.8mF with 200V caps,
>but I will be increasing the size anyway soon.
>I am just trying to make something that will be farily future proof
>for my designs.
You might do with a simple current limitter. Rectify the mains and
charge the capacitors from the mains. When the current gets too high,
disconnect the capacitors (with a MOSFET) and reconnect them at the
next cycle. This will give you a horrible power factor (like most SMPS
anyway), but will charge your capacitors within a few cycles.
You could set the current limit at 10 to 20A without any problem
(you'll only be charging during half the mains cycle so the effective
current is roughly half of the limit you set).
Needless to say your circuit will be connected to the mains
Reply to nico@nctdevpuntnl (punt=.)