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Old 18th November 2006, 06:28 PM   #1
roger-k is offline roger-k  Norway
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Default A question about powersupply fuses?

I want to make a powersupply, for a preamp. (look at the attachment)
Are the fuses F1 an F2 necessary or is it enough with just a fuse at the primary-side of the transformer?
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Old 18th November 2006, 07:21 PM   #2
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If the bridge rectifier shorts they(F1orF2) will open the secondary circuit and prevent your transformer from burning-up cheap insurance.
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Old 18th November 2006, 07:27 PM   #3
lgabco is offline lgabco  Slovakia
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Fuses F3 and F4 are not necessary. F1 and F2 are enough.
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Old 18th November 2006, 07:58 PM   #4
roger-k is offline roger-k  Norway
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OK. Thank you very much for the answers.
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Old 19th November 2006, 10:05 AM   #5
roger-k is offline roger-k  Norway
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Hmm.... but....
If I do nat have F1 and F2. What will happen if I get a short-circuit in one of the diodes (or the rectifyer).
Will not the fuse at the primary-side (process side) of the transformer blow, before the transformer is getting damaged?
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Old 19th November 2006, 10:17 AM   #6
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Which is size of transformer ?
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Old 19th November 2006, 10:30 AM   #7
AndrewT is online now AndrewT  Scotland
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Hi,
F3 & F4 kill the source impedance of the PSU.
move then to between C3 and C5 and between C4 and C6.

The primary fuse IF CLOSE RATED can be used for effective transformer shutdown if the output goes wrong.
Fusing does not protect any internal components.
They are there to stop the house catching fire.
DO NOT fuse the mains neutral, only fuse the mains live connection to the transformer.

Operating VA/supply voltage = operating current= close rated fuse.
Use a T rated fuse (anti-surge) to allow switch on and short term transients.
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Old 19th November 2006, 01:30 PM   #8
lineup is offline lineup  Sweden
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Quote:
Originally posted by AndrewT

F3 & F4 ....
move them to between C3 and C5 and between C4 and C6.
quite right!

Best place is AFTER the first Big Filter Capacitors.

If placed before these Electrolytics, then fuses might blow
if and when electrolytics are charged by high inrush currents at Startup.

As already told,
place before regulation will not disturb the clean output of regulator.
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