From: Roger Johansson
Subject: Re: 1.6V zener diodes?
Date: Mon, 14 Oct 2002 18:48:55 +0200
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email@example.com (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.)
>yet you warn that for a LED the
>volatge depends on the curtrent?
Well, I rather say that you can regulate the voltage through the
current, if you need a voltage reference at a voltage which is a bit
lower than at normal led currents.
But then you need an amplifier as a buffer to get a low impedance
output, if you need that.
>Strictly speaking you are right
>(like: the output voltage of a 7805 depends on the input voltage), but
>it is still a bit strange.
The voltage is more constant with changing currents in a led than in a
but of course you can choose a current which gives you more exactly
the voltage you need, maybe a thousand times less than normally for a
led, for example.
The voltage to current relationship is a logaritmic curve all the way
from very low currents, in zeners, leds, and other bipolar
semiconductor PN junctions.