From: Chuck Simmons
Organization: You jest.
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Subject: Re: 1.6V zener diodes?
References: <email@example.com> <firstname.lastname@example.org> <email@example.com>
Date: Mon, 14 Oct 2002 18:19:51 GMT
NNTP-Posting-Date: Mon, 14 Oct 2002 11:19:51 PDT
Roger Johansson wrote:
> firstname.lastname@example.org (Wouter van Ooijen (www.voti.nl)) wrote:
> >>A led is a better zener than a real zener, and is available in
> >>voltages close to 1.6V. The exact voltage depends on the current.
> >So a LED is better than a zener (main function: almost the same
> >volatge over some range of current),
> Yes, the voltage is less dependent upon the current than in a zener.
> Or you could say that a led has a sharper knee.
> (But the knee is actually an illusion built upon the choice of scales
> in a diagram, the response is purely logaritmic.)
I don't think this is quite right. As I understand it, below about 5
volts, zener diodes operate according to the zener effect which is
quantum tunneling in the depletion region. The kind of statistics
involved in tunneling are not likely to give a characteristic similar to
diode forward characteristics. Above about 5 volts, the mechanism
changes to avalanche across the depletion region. Avalanche is very
abrupt and does not fit a logarithmic curve. In transistors, avalanche
can produce a negative voltage-current slope. Moreover, the forward
voltage drop of a silicon diode has a 2.2 millivolt/degree C temperature
coefficient. Reverse breakdown does not behave that way. Also noteworthy
is that I rather think the forward drop of an LED has an even higher
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons email@example.com