Steve Thompson wrote:
>
>>For an inductive input filter the RMS ripple current is equal to the output
>current if you have a >single phase supply. For a capacitive input
>filter the max ripple current will be equal to the >square root of 2
>(1.414) times the DC output current.
>
>
>Doesn't it vary with source resistance and C/R values? I use a rule of
>thumb of 3x for capacitive input - it was very instructive putting a .1
>ohm resistor in the bottom of the capacitor stack and hanging a 'scope
>across it. The example circuit in the Duncan software has a cap input
>PSU putting 450V across 5k. DC current is 89mA, rms current in the cap
>is 226mA and 248mA in the transformer winding.
I haven't checked that example, but one "gotcha" in the Duncan program
is that the default results in the tables include the power-on cycles
where current can be very high.
The solution is to set the "Report from" time a few cycles in.
Also the original PSU Designer did not include high-voltage rectifiers
like we use. If you go to the PSUD site via
www.ifwtech.co.uk/g3sek/in-prac/index.htm (scroll down to August 2001)
then you can see more details and also download a modified
RECTIFIERS.TXT file which includes a typical high-voltage string of
6*1N5408
PSU Designer is very highly recommended - it can answer just about all
your power supply questions.
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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