How can I investigate the current in a diode as the temperature varies?

Question

Hi,

please advise, thanks!

Answer 1

See the reference web sites below. Note that you need a sensitive voltmeter and a variable constant-current source in the region of 0.1 to 10 ma. It's also important to minimize the effect of self-heating, in which the test current times the diode voltage drop results in a certain amount of power dissipation in the diode itself, raising its temperature above the presumed test temperature. For best accuracy, if several diodes are involved, each diode should be individually calibrated since there are minor variations between diodes. You can use either a simple diode or, for better linearity, a diode-connected transistor (base connected to collector). Depending on linearity of the diode and your accuracy needs, either a two-point calibration (two test currents) is needed or a single-point calibration is adequate. I'd start with the single-point and see if you get good linearity over a decent temperature range.
Ref. 1 provides a useful introduction and suggests a 10:1 ratio of currents in two-point calibration.
Ref. 2 is an application note that describes selection of the operating point (i.e., how much test current to use) for single-point measurement. You probably know that as current is increased, the voltage drop of a diode rapidly increases from 0 and then becomes limited. The result is an I-vs-V curve with a "knee". The operating point should be somewhere near the knee and this means a pretty good constant-current source is needed.
The theory-based formula for two-point calibration (refs. 1, 3, 4) is in the form
V2 - V1 = kT/q * ln(I2 / I1)
where k is Boltzmann's constant (1.38E-23 J/degK) and q is the charge of an electron (1.6E-19 Coulombs).
Thus T = 11594 * (V2 - V1) * ln(I2 / I1)
Note that T in all formulas is in degrees K.

Answer 2

Well, you will have to change the temperature and measure it with a thermometer while you record the electrical measurements. And it is much easier to put a constant current through the diode and then measure the voltage than the other way round.

Answer 3

I as quickly as had to handle this project professionally, finding out complicated digital kit. Your approach for cooling/heating is only the initiating of the project. Your important project is the TEMPERATURE OF THE JUNCTION! the main precise length is gained interior the 1st few milliseconds of change-on. consequently you may desire to rig an infra-crimson temperature length of the diode junction, as against time, and at numerous currents/skill adjustments. as quickly as you have the backside standards, you are able to proceed with the test, as quickly as returned utilising the administration IR length tool, to ensure the junction is held on the precise temperature. that's an extremely complicated and time-ingesting technique, that would desire to take some days to end!

Answer 4

Connect the circuit to an amp meter and vary a heat source across the diode, you will observe a changing reading on the meter.