Zener Diode Tutorial

We always enjoy [w2aew’s] videos, and his latest on zener diodes is no exception. In it, he asserts that all Zener diodes are not created equal. Why? You’ll have to watch the video below to find out.

Zener diodes are one of those strange items that have several uses but are not as popular as they once were. There was a time when the Zener was a reasonable way to regulate a voltage inexpensively and easily. Unfortunately the regulation characteristics were not very good, and the power lost was very high. But that was sometimes a reasonable trade, compared to putting a pass transistor and the associated discrete circuitry in place to make a linear regulator. With the advent of chips like the 7800-series regulators, you can have a high-quality regulator with one extra wire and still keep your costs under $1. Even if you want to do better and go with a switching power supply, that’s easy now and not much more expensive.

So you don’t see as many Zener power supplies as you used to. But there are still cases where they are useful. For example as part of a voltage reference circuit, since they can be reasonably accurate if the load current is constant. They are also useful for clipping voltages, circuit protection, and can even be part of a random number generator that will take advantage of their inherent noise during avalanche operation.

What’s avalanche operation? Watch the end of the video and find out. This isn’t the first time we’ve talked about the lowly Zener. We’ve also talked about Zeners and Schottky diodes, too.

22 thoughts on “Zener Diode Tutorial

    1. Too late – that’s what they’re called. He can feel free to call them whatever he wants. What’s worse is, many of the diodes we call “zeners” are actually avalanche diodes, which use a completely different property of semiconductors, so people are calling things he had nothing to do with by his name.

    2. Although I write software for a living, much of it has been embedded, so I read a lot about hardware, and I have [i]never[/i] seen a Zener diode referred to as a “Z-diode”.
      Alexander Graham Bell thought people should answer the phone with “Ahoy!”, don’t hear that much either.

  1. Zeners can be much much more than “reasonably accurate if the load current is constant”. If the load current is constant then they are they are exceptionally stable (which is more difficult and more important than accurate).

    Since the 1970s the voltage reference inside the highest precision commercial voltmeters has been a zener diode. For example, the current “champion”, the HP/Agilent3548A is based on an LTZ1000.

    If you want better, then you have to use Josephson junctions!

  2. Don’t you think that somewhere inside those IC regulators and switching power supplies there is a voltage reference based on a semiconductor band gap? Zeners still exist and are everywhere, you just don’t see them because they’re embedded in a larger component.

  3. Zeners are also handy if you’ve got a case where a chip has multiple supply voltages, and they always have to be within a certain delta-V of each other (so two separate regulators that turn on independently wouldn’t work, and a second regulator sequenced off the first also won’t work). You can get regulators with startup tracking, but they’re much rarer than you’d expect, and if it’s just one chip with a small current draw that requires it, it can be a pain to find one that fits.

    Cypress’s Versatile I/O feature on their SPI flash chips (that allow a different I/O voltage than the core voltage) are a good example here, requiring Vcc-0.2V < Vio < Vcc until Vio is above 1.65V.

    1. Well you know what I meant, surely. Designs that use discrete zener diodes — I didn’t think I needed to be that explicit. Of course, zeners still exist in the IC but they are usually subsurface (probably not on cheap 7800 parts but I don’t know that for sure) and also surrounded by circuitry to ensure the reference load is constant.

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