[Amps] Diode Bias Strings

[2]

>>  //Geesh, I find I have to correct myself! (What else is new?)  The Vf
>> tempco of a standard Si rectifier   isn't negative, it's positive.  

**  At this QTH, the hotter the junction gets, the lower the Vf.  Try 
some espresso. 


>> The hotter it gets, the higher the Vf.  I still haven't had coffee...gotta 
go
>> for some, I think!
>> 
>> -WB2WIK/6
>> 
>> > 
>> > //That Vf/If curve, e.g., 734mV/100mA and 813mV/1.2A, may be true for
>> the
>> > 1N5408 tested, but isn't necessarily representative of all 3A
>> rectifiers.
>> > In fact, Vf is normally only specified as a "max" at full current, and
>> > nowhere else, and can run all over the place.  I've seen lots of 3A
>> > rectifiers having <<500mV @ 100mA, and >>0.8V @ 1.2A.  The "Vf max" of
>> > most mil-spec 3A rectifiers, of which the 1N5408 is not (but the very
>> > similar 1N5554 is), is 1.0V @ 3A, and of course it has a negative
>> tempco,
>> > meaning the hotter it gets, the lower the Vf will be.  If each rectifier
>> > had a 250mV delta Vf, and ten were used in series, this is a 2.5V delta
>> > Vf.  Could be quite a lot, in some cases.
>> > 
>> > -WB2WIK/6
>> > 
>> > 
>> > 
>> > 
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-  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K, 
www.vcnet.com/measures.  
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