 The Great Search brought to you by Digikey and Adafruit every single little week. Lady user powered engineer to help you. Yes, you find things that you want at digikey.com. Lady, what is a great search of the week this week? This week we're looking at Zener diodes. So let's go to the computer and I'll show my moment of Zener. So Zener diodes are great for a bazillion things. One of the projects that I've been working on is this protocol interface that is supposed to be five volt compliant and one of the ways I'm doing that is using this Zener clamp to make sure that the inputs coming into these GPIO pins never really get above 3.3, 3.6 volts. And I've realized, you know, people will realize how amazingly wonderful Zener diodes are. They're great. They're wonderful. I mean, they're a dessert topping and a floor wax. Some fun tips can be found in this document. It's just called the three-volt tips and tricks. And the particular technique that I mentioned, there's actually a couple in here. So one is using a Zener as a very low-cost regulator or power supplier, like whenever you need a voltage reference, plus minus 10 volts. It's not precision, but sometimes it's okay. Sometimes you're just like, look, I just need about three volt input to buy us something. You just need a resistor and current going into the Zener diode. And this will kind of sit at whatever, you know, this is rated as the 3.6 volt Zener. This will be around 3.6 volts. So that's a Zener power supply. And there's a couple notes about it. A Zener clamp, that's the voltage protection circuit that I mentioned before. The voltage going into here, as long as this resistor makes the bias into D1 about five milliamps or so, or less. Yeah, we're like five milliamps. I mean, it's not, you depend on the wattage. This V out won't exceed the reverse voltage of the Zener diode. There's also a great tutorial by Evil Mad Scientist. It's over 10 years old, but Zener diode never go out of style. So check it out. Interaction to Zener diodes by EMSL, wonderful scientist over in California. And I tackle all the different tips and tricks that they use Zener's for. Again, like simple voltage regulators, level shifters, making, you know, stacking them up to make multiple reference outputs from a higher voltage supply. Because they'll have that positive, they act like a normal diode when forward biased with like a 0.7 volt drop. But on the reverse bias, they can have an adjustable drop. And so when you purchase the Zener diode, you'll have to specify what the reverse voltage breakdown voltage you want is. And we'll show that more tips and tricks. Here's a fun one, you know, they use this to drop a 36 volts input into a five volt regulator. They just need to like lose 10, 12 volts, a 12 volt Zener will do it, as long as it's rated for the amount of current. And then the voltage drop across it. So that's something to watch for. Zener diodes, let's go to Digi-Key and check what they've got. First off, you might be wondering, am I at the Digi-Key site? Because the logo looks different. They just did a logo refresh. They're going with a brighter red color, which I like. And they're losing the dash in the Digi-Key. I think they did a post on social media also about their rebranding. I like it's a little bit more modern. I personally think that the D, like the D in the center of the D, like reminds you of the catalog sitting on my shelf for, you know, decades. Maybe that's what the D stands for. So they've got Zener diodes, do they ever? Hundreds of thousands of them almost. So there's Zener kits and there's Zener diode arrays, but we'll just look for the single Zener diodes looking for, you know, active ones in stock, not marketplace. So it gives us down to, you know, 9,000. So the reverse voltage, so there's a couple of standard voltages. There's a few, you know, families that are popular. I tend to use the MM series. It's made by, you know, they're made by multiple different manufacturers, and they come in kind of set voltages, like every 0.3 volts. So it's like 1.8, 2.1, 2.4, 2.7, 3.0, 3.3, 3.6, etc, etc. They go very, very high. But for what I often am using the Unisport, which is again, clamping a signal down from, say, 5 volts down to 3.3 volts, I let you use a 3.6 volt Zener. Now, you might be wondering, why aren't you using a 3.3 volt? Because oftentimes, I'm not biasing with a full 5 milliamps, and most of them are rated, that voltage that they're rated at, the nominal voltage, you only get when you're putting a significant amount of current through. But if I'm caking this up to some other digital signal, I'm not usually getting a full 5 milliamps. In fact, this 1k resistor is limiting me to your 1.5 volts across, 1.5 milliamps through the 1k resistor. So this is going to be, you know, 1.5 milliamps. I've measured it, it never quite gets to 3.6. It's usually like 3.2, 3.3. So let's look at, again, but you can get any voltage you could possibly want, including 3.3. So let's look at 3.6 volt Zener, and then I'm going to do surface mount, because personally, I'm going to be using surface mount, but they have through hole, you know, it's one thing you can definitely get through hole forever, Arzina diodes. And basically, you can get, you know, any package you like. And the thing you're going to want to watch for is, oh wait, did I click 3.3? Sorry, I meant 3.6. So let me, let me delete the nominal voltage, and then go back, and I'm going to select nominal 3.6. That's what we meant. Apply, and then don't forget, you always have to have, you know, Zener diodes, they only work when there is a resistor. You always have to have a resistor to limit the current and the voltage that's going to appear at the, so that this reverse voltage has, there's some, the Zener diode has like a 3.6 volt reverse voltage. If you try to put full five volts directly on it, it doesn't like regulate it, it'll try to pass all that voltage through, it'll draw a lot of current and it'll blow up. So you need to have much like an LED needs a choke resistor, you do need to calculate your choke resistor. How do you calculate it? It depends on the milliwattage of the diode. So you have to figure out with that voltage drop across the reverse biased Zener 3.3, 3.6 and how much current is going through it, you can't go above the milliwattage. So it's a trade-off, right? If you're, if you're trying to drop a huge amount of voltage with a lot of current, you're going to have to go big. So these tiny sod 323s, you know, good for this little 1.5 to 5 milliamps little, little signal level shifters. If you're trying to use it in a power supply, like we showed with the Evilman scientist example of using it to drop voltage into a regulator, you're going to need something much, much bigger. You'll need like a one watt or a two watt Zener and they make them in those wattage, but you might have to go through hole to get that physical size. Or you could always, you know, use multiple ones. This one looks like, you know, it's chunky. It's a DO 219AB 800 milliwatts. You can get them in, you know, you can look up here for the PowerMax. You can get them up to like a watt or one and a half. But again, we're doing it for signal. We don't really care. And I do like the sod 323. I want it to be nice and compact. So I'm going to pick that for the size. The rest, the 123s are a little bit bigger. I don't, I want to kind of minimize space. And, you know, there's, there's, there's a lot, but this one's a really, you know, two, two and a half cents on semi. So I know that they're going to be able to always have them in stock. I'm not going to zoom in. Come and tape in real. And then, you know, look at the datasheet for specification. I will say that they're jelly bean parts. The MM3Z series, you know, they're available from multiple vendors. They'll just have that different 3v6 where the XXX is in the, in the datasheet. You'll get different voltages from 2.4 to 775 volts. But it's still not a bad idea to look, especially if there's an impedance and what current it's expected. Again, 5 milliamps is pretty common. That's a good idea to look. And the variation, you will get variations for the 3v6, like I said, can go as low as 3.4 to 3.8 at 5 milliamps. But I don't usually drive them at that current, usually drive them at a lower one. It looks like once you get to the higher voltages, they're expected to be driven at 2 milliamps instead. So Xeter diodes, they're amazing. Really, they do everything. I love to throw them into my designs for all sorts of like random voltage reference protection circuitry. And they're really cheap, two cents. So check out some of those links. We'll have them in the description so you can read the Evil Mad Scientist Guide, as well as the microchipped Google tips and tricks PDF. For these wonderful Xeter diodes.