Electronics > Projects, Designs, and Technical Stuff
Measured zener voltages
TimFox:
How much resolution on the Zener voltage do you need, and what can you get on your digital oscilloscope? 1% resolution should be easily achievable on an 8-bit scope.
srb1954:
Yes, but it will be difficult to get accurate measurements due to the limited resolution and quantisation noise of the average scope (I am assuming you are using a digital scope and it is not one of the super-expensive high-resolution models).
You could get more accurate measurements with a scope that has a differential comparator input. You use this to offset the nominal Zener voltage from the measurement so you can view and measure small deviations from that offset voltage. AFAIK such capability is not available in modern scopes and you have to revert to an old-fashioned analog scope e.g. Tektronix 7000 series with a 7A13 differential comparator plug-in.
The most accurate way to measure the Zener voltage under pulse conditions would be to use a a high-speed digitiser such as found in high-end bench multimeters or data acquisition systems. This could be triggered to take a fast measurement or series of rapid measurements a short time (allowing for the Zener voltage to settle) after the current is applied to the Zener.
Alternatively, you could build your own test system using a fast ADC, 14-bit or better, paired with the micro of your choice.
exe:
I wonder how much it makes sense to measure zener clamping voltage with pulsing current. This is not a normal operating condition, what's the use of it? I understand why bjts are measured this way: to match them better. But zener... (except currents that would normally destroy them in seconds).
srb1954:
Zeners are frequently used as clamping devices to limit transient voltages and protect sensitive circuitry. Compared to other clamping devices e.g. MOVs they have the advantage of responding very quickly and clamping transients to tightly controlled levels. Since in this application the Zener is usually clamping short transient signals it is highly desirable to be able to measure the Zener performance under pulse conditions without the complicating effects of thermally induced drift.
It is probably fair to say that the main usage of discrete Zeners these days is for clamping circuits. Previous applications of Zeners as voltage regulators and reference voltages have largely been superseded by better performing and more efficient monolithic voltage regulators and band-gap reference circuits respectively.
magic:
Actually, there are dedicated ESD protection devices too, with low leakage, sharp knee, guaranteed clamping voltages at a few amps of current and whatnot.
Not even sure if they are (modified?) zeners/avalanche diodes or perhaps some small ICs :scared:
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