Good morning to diode lover's the world over,
I'd just like to toss a couple of facts into the milieu...
1. Maximum Non-Repetitive Surge Current has a number of values depending
on the time of the applied surge. For ½ wave (what a single diode
usually sees) 60 Hz operating conditions the value ranges for a 1N5408
from 200 amps peak for a single ½ cycle to 50 amps peak for one hundred ½
cycles. The graph can be found on a complete 1N5408 data sheet pp
3-45,46 Motorola DL125 Rev. 2.
2. The Maximum Repetitive Surge Current such as seen in a capacitor input
filter varies depending upon the impedances of the other circuit elements
but, a typical value would be around 8-10 times the average output
current. Therefore, a diode operating at 2A average output in this
instance is subjected to approximately 20A peak currents. Whether this
is within the diodes safe operating area depends mostly on how it is
mounted since the leads provide much of the heatsinking for this part,
and the ambient temperature. There are a couple of graphs mapping this
on the same above referenced data sheet.
3. For further reading, Motorola HB-214, The Rectifier Applications
Handbook, chapter 7 covers capacitor input filters in great detail.
4. from Larry's seed posting
>So here's the question: why did the highly acclaimed 1N5408's fail? Are
3
>amp diodes in a bridge not enough for a capacitor filter supply with
over 2
>amps DC output capability?
From the references noted above the answer is marginal, unless you
have excellent heat transfer. I suggest you go with the next larger (6A)
diode. MR760 used to be a good part number for this... I don't know if
it's still available.
5. Save your old databooks. The new ones just don't give any real design
info for 30 year old parts!
73,
Marv WC6W
*
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