Re: schottky tempco
- From: gearhead <nospam@xxxxxxxxxxxx>
- Date: Fri, 14 Dec 2007 12:02:50 -0800 (PST)
On Dec 12, 4:55 pm, gearhead <nos...@xxxxxxxxxxxx> wrote:
On Dec 12, 1:23 pm, gearhead <nos...@xxxxxxxxxxxx> wrote:
Apparently temperature coefficient varies with the log of the currentAfter manipulating the Shockley equation algebraically, I came up with
according to the shockley equation. If I can determine the parameters
(like the ideality factor) for a particular schottky I can get the
math worked out and fiddle with the current setting to get the
temperature characteristic of the circuit right.
an interesting result. Assuming that a diode actually obeys the
Shockley equation, then you can take some measurements of the diode at
room temperature and calculate the temperature coefficient from those
results.
Assuming you only need to deal with currents well above the saturation
current, which of course is the case in the vast majority of practical
circuits, you can characterize the diode's behavior with an equation
of the form
ln I = a Vf + b
where I is the diode current and Vf is the voltage across the diode
Let T' represent the temperature in Kelvins at which you determine the
parameters a and b.
Then the diode's temperature coefficient = (ln I - b) / (T' x a)
(b is a negative number)
I did this for a 1N4003, 1N4148, 1N5818 schottky and MBR3035PT
schottky, also a pink led.
the schottkys have a lower tempco than the standard silicon diodes.
Also, schottkys have an emission coefficient near unity.
I thought this was pretty slick. As expected, there's a wide current
range for which standard silicon diodes have a temperature coefficient
near 2.2 mV/K.
But having this formula makes life easier. Takes some of the
guesswork out.
.
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