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Old 15th February 2003, 01:38 PM   #1
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Post Ultrafast Diode bridge substitution

I've come to a delema in my car amp project planning.
I definatly need fast diodes for the rectifing but I don't have access to any bridges that even mention fast.
the Biggest diode I can get are 1 amp 100v (or 1000v bu it wno't make 2 much difference).
Can these be used for 6amp purposes with heatsinking?
how many would be needed to pull this off?
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Old 15th February 2003, 01:56 PM   #2
blmn is offline blmn  Brazil
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fr0st,

No, you can't. But, if they were ultrafast too you can put six of them in paralell to achieve your current needs. It's not the best option, in my opinion and I've never tried it before with six diodes, but, considering your information, you have no choice.

Regards
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Old 15th February 2003, 01:58 PM   #3
Ren is offline Ren  United States
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See the Michael Percy Audio catalog for a listing of available high speed rectification diodes and bridges. He lists IXYS 20A, 600V high speed bridges but they are expensive: $17 US. I just bought some discreet IR HEXFRED 8A, 600V diodes from Digikey for $1.32 US each (qty = 10). Don't know about sources for these parts on your side of the globe.

Ren
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Old 15th February 2003, 02:33 PM   #4
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Question Farnell?

Have you checked with Farnell? I did a search on FRED's and got a few hits without too much trouble at their website:

Farnell Australia.

Check it out and see.

Later,
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Old 15th February 2003, 05:24 PM   #5
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Default Re: Ultrafast Diode bridge substitution

Quote:
Originally posted by fr0st
I've come to a delema in my car amp project planning.
I definatly need fast diodes for the rectifing but I don't have access to any bridges that even mention fast.
What frequency are we talking about?
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Old 15th February 2003, 07:39 PM   #6
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Be careful when putting diodes in parallel as the currents don't divide equally: the diode with the lowest forward voltage drop will take the majority of current because it limits the turn-on of the others in the array.

Nice one,
David.
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Old 16th February 2003, 04:08 AM   #7
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Quote:
What frequency are we talking about?
50khz
I've been looking through Farnells site and they got heaps exept I don't know exactly what to look for
I found this here
Can anyone recommened one from thier range? coz I really don't know what to look for in diodes.
Also they sell coated ferrite cores . How would these compare to your normal cores (wattage wise)?
Thanks
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Old 16th February 2003, 04:29 AM   #8
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bahh.... I should never post when tired
I found some TO 220 15a fast diodes in a electronics catalogue of a place near me which suits me perfectly.
I still have a question about the core sizing.
can a 3.5cm core withstand 400watts?
It will have cooling (fan forced) and suitable gauge winding.
Thanks for your help
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Old 16th February 2003, 05:30 AM   #9
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Quote:
Originally posted by fr0st
I still have a question about the core sizing.
can a 3.5cm core withstand 400watts?
I assume when you say 3.5cm, you mean the area of the core in square centimeters? If so, then it depends on the average path length of the core. (ie, it's basically the mass of the core, not just the area)

I have a core here, it's area is about 1.38cm squared, and the effective length of the core is about 13cm long. It's a torroid about 4.8 cm od, 3.2cm id, by 1.7 cm thick and I've tested it at 1300W. So if you're anywhere near that size at 50Khz, I'd say 400W should be no problem.

BTW, if anyone knows how to calculate the power a core is good for, I'd be interested in knowing how do to it myself. I've always used the WaAc method from the Mfr specs. I still think that there is a better way of doing it. (Maybe what I really need is a good book on magnetics for SMPS supplies???)

-Dan
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Old 16th February 2003, 08:30 AM   #10
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Quote:
Originally posted by dkemppai


I assume when you say 3.5cm, you mean the area of the core in square centimeters? If so, then it depends on the average path length of the core. (ie, it's basically the mass of the core, not just the area)

I have a core here, it's area is about 1.38cm squared, and the effective length of the core is about 13cm long. It's a torroid about 4.8 cm od, 3.2cm id, by 1.7 cm thick and I've tested it at 1300W. So if you're anywhere near that size at 50Khz, I'd say 400W should be no problem.

BTW, if anyone knows how to calculate the power a core is good for, I'd be interested in knowing how do to it myself. I've always used the WaAc method from the Mfr specs. I still think that there is a better way of doing it. (Maybe what I really need is a good book on magnetics for SMPS supplies???)

-Dan
This is my first SMPS so i'm still learning the parmeters to quote.
The core 35mm Od, 21mm ID and 13mm high.
I'll just assume it'll work and I'll incorerate a thermal fuse just incase.
Thanks
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