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Measured zener voltages

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TimFox:
Zeners around 6 V have the best tempco.  6.8 V reference Zeners are a 6.2 V Zener and a forward-biased PN junction in series, so that their tempcos cancel at a specified current.  There are similar devices with two or three PN junctions to get higher reference voltages.

paulossant:

--- Quote from: srb1954 on July 10, 2020, 12:46:34 pm ---Testing with 100mA Zener current is going to cause significant self-heating in the diodes, particularly if they are small packages. This will affect the shape of the curve due to the temperature coefficient of the Zener voltage - positive for voltages above 6V and negative for voltages below 5V, approximately zero between 5V and 6V.

If you really need to test the Zener voltage at high currents e.g. for clamping circuits you need to use a pulsed current technique to determine the true voltage vs current curve.

--- End quote ---
I have taken the temperature effects into consideration. To more precise, I tested the zener diodes with mine diy constant current load.
I saw the temperature dependence affecting the readings, so for currents bigger than 25mA i have done that exact pulse measurements (by turning on and off for about 3-4 seconds, allowing me to take note of the values)

my diy constant load was not good for currents below 300uA, therefore the lack of measurements bellow that value, but I can test it with other setup.

srb1954:
Applying test currents 3-4 seconds is still too long to avoid temperature effects. You really need to be looking at millisecond length test pulses to avoid excessive junction heating.

It is not the overall case temperature that matters but that of the small semiconductor junction in the centre of the diode. These have a very small thermal capacity and don't take long (<100ms) to heat up.

TimFox:
I noticed how strong was the self-heating effect in 1 W Zeners when I tested 62 V diodes (axial lead) on a Grayhill test clip fixture (plugged directly into a DVM, fed from a current source), and saw how the voltage changed when I pinched the diode between thumb and forefinger.

paulossant:

--- Quote from: srb1954 on July 10, 2020, 02:19:42 pm ---Applying test currents 3-4 seconds is still too long to avoid temperature effects. You really need to be looking at millisecond length test pulses to avoid excessive junction heating.

It is not the overall case temperature that matters but that of the small semiconductor junction in the centre of the diode. These have a very small thermal capacity and don't take long (<100ms) to heat up.

--- End quote ---

Testing both ways should give an interesting comparison. I will arrange a setup, maybe a micro with a one time shot pulse (25ms), acting on a transistor to turn on a voltage source momentarily, and just get a resistor and the zener, with a scope on the zener. Would that be a good way to test?

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