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Registered Member #192
Joined: Fri Feb 17 2006, 03:08AM
Location: Canada
Posts: 44
Hello,
I was trying to find a manufacturer that I could sample some diodes from. I need 20 amp ones in a TO-220 or TO-247 type of case.
Also where can I get mini brick diodes, SOT-227s also called ISOTOPs. I tried Fairchild and the ones that they have are 33 amps, I need a higher current rating at 600 volts.
thanks,
edit: I just found them at st.com, they carry both kinds. thanks anyway ! If anyone knows of other manufacturers please let me know.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Last time I checked (summer) failrchild still samples... But I doubt you will find any minibricks up for sample.
Also, what rating of a diode do you need? 30a/600v is 18kw... BTW, The peak current is orders of magnitude higher that the average (diodes and scr's have enormously high peak ratings compared to igbts or wore yet fets).
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
30a/600v is 18kw...
Sorry, that just struck a nerve. Its comments like that, which spread misconceptions. Its like giving a MOSFET some obsene KW rating by multiplying its stand off voltage and max current when in fact, such a number is COMPLETELY MEANINGLESS.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
Actually MUR3020 CAN provide 200V @ 30A dc average = 6 kW
Why does the description upset you Steve?
O.K. I admit that's running on the edge, but technically feasible and in a TYPICAL circuit a less than (for safety margin) +/- 100Vpeak waveform is common so Vdc <= 100V but other circuit configurations can be possible.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
You must always also consider safety margin for current, and consider maximum power dissipation you can allow to diode with your heatsinking capabilities. If it is a HF rectifier you also need to account recovry losses and etc, etc. So those numbers probably are more or less meaningless.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
The thing is, you speak as if you are rectifying an already DC power source. In most power applications, the diode current is usually transient and periodic, where the actual power "processed" is considerably smaller than multiplying Vbreakdown by Iconduction. This doesnt even get into power factor either, so saying VA might be slightly less annoying, but its still silly to give semiconductors a "power" rating in my opinion (unless you are speaking of power dissipation).
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
TRUE!
That's why I noted a 200V rectifier in TYPICAL circuits will only provide <= 100Vdc at rated current So for example a squarewave OR sinewave ac source could only supply 3kW maximum continuous power via MUR3020 to stay within ratings, but for pulsed uni-polar sources 6kW IS achievable. (e.g. forward convertor)
I'm not saying that a reasonably well profesionally designed system would use semiconductors so close to the limit, myself I usually use very conservative safety margins even for hobby use as a little more cost in semiconductors saves a lot of frustrations, but in these forums we often use semiconductors well beyond spec.sheet current ratings.
Anyway, this is off topic so I'll cease this line of discussion now, unless there are any serious rebuttals.
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Where to get high current diodes?
when in fact, such a number is COMPLETELY MEANINGLESS.
