Yep, the standard tempco of an ordinary rectifier is negative! Geesh.
However, there are exceptions, such as zeners, which have a positive tempco,
and 6.2V LVAs which have zero tempco, etc.
I'm really sleepy, and the espresso didn't help (yet)! $3.00 for a
Cappucino at Starbucks, you'd think it would have some kick.
WB2WIK/6
"If everything seems under control, you're just not going fast enough." -
Mario Andretti
> -----Original Message-----
> From: 2 [SMTP:2@vc.net]
> Sent: Friday, July 19, 2002 11:07 AM
> To: Steve Katz; Marv Gonsior ; AMPS
> Subject: RE: [Amps] Diode Bias Strings
>
>
> >> //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.
> end
>
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