Fans and switched mode PSUs

[Ken Stone]

>    Question: how badly do the switch mode PSUs you get in external drive
cases need their small , noisy, and intrusive fans? I'm thinking of using
one as a PSU for some ccts (Yes, I know they give out interference like a
small star).

Very badly. Kill the fan, you cook the supply. Since you are only lightly
loading it, consider putting a few diodes in series with the fan voltage
(assuming it's a 12 v fan) and reduce its speed and noise that way.

>a) dispense with the fan altogether; I won't be pushing the PSU hard at all.

bad idea. I've seen major damage result when fans have failed. Cooked filter
capacitors  for example.

>b) swap the fan for a thermally controlled 'low-noise' replacement. The
best noise figure I've seen for these is 24dBA, from Farnell in the UK.

possible.

Best idea:  Use linear power supply.

Ken (the hypocrite, who does have a switchmode in one of his modules.) 

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                Ken Stone  sasami at blaze.net.au
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