The voltage the diodes must withstand depends on the configuration of the circuit, as well as the voltage.
For a 4 diode bridge, there is no more than peak line voltage across any device.
Are you connecting the diode bridge, directly to the 230 volt line without any transformer to isolate or change the voltage?
If the bridge is fed with 230 VRMS, then the repetitive peak voltage across any diode will be sqrt (2) * 230 = 325 volts. But you want to handle more than nominal + 10% (358) before something pops. I would use a 600 PRV rated or 1000 PRV rated diode. But that won't produce anything near 40 volts out.
Look at the data sheet:
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1N5407 is rated for 800 volts reverse repetitive.
At a 900 watt level, the ripple current is going to be pretty high, so you should buy a unit that meets this requirement, specifically. But I am confused. You talk of rectifying 230 volts and of outputting 40 volts. You need a very different capacitor for a rectifier across
230 volts than you need for a rectified transformer output that produces 40 volts.
I'll assume, for the moment you have forgotten the transformer, and you actually will have a source of about 28 to 30 volts AC. The output current will be about 900/40=22.5 amperes, so your bridge diodes will need to handle at least 11.25 amperes, each. Of course, their reverse voltage requirement will be only about 40 volts, so 100 volt units would do fine. Or you could just use a prepackaged bridge rated for something like 25 to 35 amperes (mounted on a heat sink, of course) and 100 volts. Something like:
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The capacitor will have to handle a ripple current of something like the DC output current (because the rectifiers charge it with narrow pulses at the peak of each half cycle. So you will probably need either a number of smaller capacitors in parallel like 20 of 1500uF 63 volts:
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Or perhaps, 10 of 3,300uF, 63 volt like:
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or a couple computer grade cap with screw terminals, for instance
900W @ 40V... that's 22.5A dc on the output side. Pretty beefy supply to take on as a first off project.
Since you mention a bridge rectifier on the mains 230Vac side are you talking about a switch mode supply? If so then you are going to require the inclusion of EMI/RFI filtering and power factor correction.
I refer you to an ST Microelectronics application note for a 500W power factor corrector for use ahead of the DC supply proper
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This explains the input rectifier requirements and you will see that they recommend a bridge with 600V piv and 25A Iaverage just for 500W output, so the items to supply 900W are going to be even more complex... and expensive. Following the PFC you are then going to have to design the SMPS proper.
I would strongly recommend that you try something a little simpler as a first attempt. Perhaps a transformer isolated power supply would be more within your capability. And even then, depending on your output requiremnets, the transformer alone may not be too cheap before you buy the rest of the components.
build a 9W power supply first. If you survive (230Vac will *kill* you if you dont respect it, and DC is a *lot* more dangerous), then build a 90W psu. Only then have a crack at 900W.
This is a common myth the only difference is whether you shake while you die. 230V is more than, more than enough to drive the current needed to kill. If it happens to connect to you body such that the stronger muscles pull it into better contact, you will die. If you when you touch it, the hand is snatched away, you will say words people would rather not hear.
The DC bus comes from the AC by means of rectifiers. Both can produce zillions of amps into a short for the time it takes for the fuse to blow. The impedance of the mains connections are very low.
No, a good fuse will blow if a current over its designed limit flows through it for a while. Remember the I^2T ratings. This means that a whole lot of Watts can get through one for a short time.
I'll grant you the point about the large storage capacitors but I don't think the OP was into that range.
I agree that the OP should be very careful. Don't take my disagreement about some of the fine points of what happens in the seconds after the mistake kills you as any comfort.
yep. but a good fuse will limit the fault current to a value less than the rated supply fault current (or it will explode catastrophically :).
I should also add I'm not talking pissy little fuses here, or wimpy domestic connections. I guess it all depends how much energy you have sitting in your DC bus. When its more than a few kJ, they are pretty nasty.
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