>
>
>> Hi Rich,
>>
>>
>> // We sell 1n5408, 1000piv, 200A peak, 3A avg. diodes for 17-cents each
>> or $14.40 per hundred. . . When mounted on perfboard, the junctions run
>> cooler than epoxy-potted diode-blocks because cooling air has better
>> access.
>>
>> ::Price is right, for sure; although the JTX1N5554 NOS surplus mil-spec
>> devices, which are more modern design and have about 1/10th the reverse
>> leakage current of 1N5408's (due to junction design, which is epitaxial
>> vs. double diffused), are also around $.17/ea or so. I buy them for that
>> price from Apex. They're factory-sealed in serialized containers,
>> although as with any "old stock," one is never totally sure of
>> availability!
>>
>> Re the cooling issue, though: As you know, axial lead rectifiers are
>> cooled via conduction, via their leads. Cooling the diode "bodies" does
>> essentially nothing, the thermal resistance from junction to air is
>> extremely high. The thermal resistance from junction to lead, however, is
>> very low. The leads must be cooled. Flowing air across the leads isn't
>> an effective way to cool diodes because the leads have such little surface
>> area (.040" diameter, typically), and if the leads are "short," this
>> situation is even worse -- now, there's essentially _no_ surface area.
>>
>> So, the modules are actually very well cooled because they are die
>> cast in a thermoset (thermally conductive) epoxy compound ...
So what is the avg current rating of the same 1n5408/3A diodes when they
are potted by K2AW? I have used potted diodes and - with the requisite
heatsink - they were larger than the low-tech perfboard version.
cheers, Steve.
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
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