 Every single weekly data user power is engineered to help you find what you're looking for or things that you don't even know You're looking for yet on digikey.com What is the great search of the week this week? Okay, so this week I'm going to be interfacing to this Apple to disk drive, which is in a beautiful clear enclosure And the Apple to disk drive has a slightly different control mechanism for how you Control the drive and read and write from it and it has this analog board and the analog board Has As you won't go my computer so I can choose an addicts. This is the schematic for the analog board the disk interface and You'll see it has a negative 12 volt power supply. So it has Plus 12 there's VCC, which is five volts and negative 12 and that's a little unusual I mean at the time it wasn't unusual because Transformer-based power supply is really easy to split the tap and then you can generate a negative voltage But with digital electronics, we don't tend to have negative power supply rails really as much So the good news is that you know most disk drives that I'm used to working with so here's the five volt supply You know your five volt supply and the ten volt supply are used for logic And there's a stepper motor probably that's the 12 volt and then there's a spinning motor probably the 12 volt or five volts So 12 volt and five volt supplies are high current they're gonna be like an amp or two because you're gonna drive a motor with them and a lot of these logic chips the Negative 12 volt supply However Let me find it Is used for a bias hold on I have like 500 images and they're all blurry Okay, so this is where the negative 12 volt supply is it's right here and it's used as part of this analog circuitry which Filters the pulses or like biases the read head I'm actually not 100% sure I have to look up at the MC 3470 dies, but this is the only place that the negative 12 volt appears So, you know it the potentiometer are 28 and you know, I looked on this Boards look at our 28 and our 28 tonight. He looks like you know, you tweak and adjust it to set The it looks like the the jitter and just the jitter for the analog board So here this is that the tech instructions for this board and they say, okay, you know, look at this Trigger pulse, I guess this is maybe the bias for the trigger Where we're like, you know, it it There's some timer and then it like reads the timer and it uses the pulses to like generate the pulse train or synchronize with The pulse train that comes out of the disc get So there's a potential you have to adjust so you do need to give it that negative 12 volts Especially, you know, you'll get weird results. If not, maybe you'll not get some some good reading results You might get errors on right. So you do want to have a negative voltage and you want to have that voltage at least be Consistent so we have to generate a negative 12 volts and again digital electronics Plop, you know, it's we've done boost converters and we've done linear Regulator so you can like kind of move up and you can move down and you need buck converters But now I want to inverter and I'm extremely lazy about this inverter because it's not a power supply It's like a bias supply. I don't need an amp of negative 12 volts If I did I would actually probably get a custom power supply to do that or put in a big You know, but boost converter buck converter that doesn't version If I only need, you know, a couple milliamps. It's a 10 k potentiometer I'm going to look for a charge pump inverter and charge pump inverters the reason I'm a fan of them is because if you remember your max 232 You know, this is a kind of a famous part not not used as much anymore, but was Famous for if you had an RS 232 interface, which all electronics used to You'd use this and it would convert your 5 volt logic or there's a version for 3 volt logic And it would do this neat thing where it was like hey since it's not a power supply that you need negative 10 and plus 10 But you just need it for biasing for signaling not for powering It would there's a built-in charge cap You would put some you know one micro farad caps on the outside It would convert the 5 volt to 10 volt and then do an inverter to get you 10 volt to negative volt So one I could probably get away with using a max 232, but I kind of want to Not cheat and use it and chip that isn't designed for it and second I might actually need negative 12. I want it to maybe be perfectly balanced. So So this is actually kind of interesting because I wasn't actually sure How to find this because you know, it's it's a it's a weird part But I think I searched for It's under regulators, so it's it's considered a DC DC switching regulator and It's actually called raciometric Which makes sense because you're not regulating it. You're just flipping it over So let's look for active Raciometric or inverted because you can also get inductor based Converters we want only one output And we want to make sure it can give you Negative hold on positive or negative. Well, let's say positive and negative and Voltage input max wait and mess something up. Let me start over This guy this was very confusing. So I want right so I want Negative I'm gonna have to go back from the part that I found and then and then go backwards. So positive or negative One output voltage input max Okay, so For voltage input max because I want to generate 12 volts. I need it to be able to take at least 12 volts So I'm going to select All of these And let's see what I get And then I don't care about it just we're fixed because I can I can tweak that And Yeah, I got a bunch of these parts and then I did surface mount only because it turns out those are a lot of two whole parts and A lot of things were out of stock so the first thing I found was there is This very popular part that's been used for a very long time called the icisl or icl 766x and there were quite a few of these and these are ancient These these have been made since the beginning of time So you can use this part most likely and there's cut that comes in at like a lot of different Manufactures is kind of a jelly bean part. So if you search for Let me open up a new page you look for icl 766 to get all the All the alternatives under the switching regulators Yeah, you'll see so this was made by like analog maxim by harris by renaissance. So lots of lots of different Lots of different options Came in dip and also smt. So this is one version. There's also this 7662 So there was this whole family However, I wanted another alternative because this was a little bit of an older chip and and there were a couple available Um, but it's sort of I was like a little I was a little Anxious about it. So the other one I found actually was the TC 1044 and this actually there's also the tc 105 for one second For Hold on let me look at my history. This was Sorry the LT 1054 Okay, so the LT 1054 was a different charge pump inverter this was available from ti and analog and The good news is this one was a little bit less expensive, but it came in a um 16 so I see so it's much much larger, but it's a much more modern chip And the pricing was pretty good. It's basically like a dollar fifty or so um, and it can do Either doubling or or negative. So it's kind of got this like weird voltage output negative v in or or two v in But the good news is that it could take up to 15 volts input. So this was actually what I ended up um picking for I thought I think I'm going to use I'm going to get some of the samples of the icl 7 6 6 0 But one thing that's interesting about that part is It's so old that it actually started getting more expensive than the modern part like usually you think like oh an old part like You know, uh Tl, you know tl 07 4 or something so you know some op amp if it's like a couple decades old It'll be really inexpensive. It's made so much the one thing I've noticed is like during the silicon shortage sometimes There's this like weird like It's it's like a there's like a dip where it's like very new parts are very expensive because you can't get them And very very old parts are very expensive too because they're like not really made anymore And so the people who need them are like desperate to not like, you know You have some like mill spec design and you're not going to change this component You absolutely need to use this component for the rest of you know human history Um, so you're desperate to get it So there's like this nice middle ground where you're actually going to get better pricing on parts that are like About five to ten years old. So um, even though this is a more modern part It actually ended up being less expensive than um, the icl which was like for some reason like Five dollars, you know for this this like multi decade old component. So the the icl Probably works really really well, but I think i'm probably going to go with the LT 1054 and I also learned a little bit about um product history and pricing I think along the way, but what's actually kind of fascinating is there's there's a lot of boost converter like the charge pump inverters For five volts, but once you get to 12 volts, it's actually kind of a little it's a little rare But this one should absolutely do the job quite nicely and uh, I'll pick it up And it's a bit chunky at 16 so I see but sizing is not as important Um, there's also a max in part that I saw that goes up to uh Plus or minus 40 volts and a TDFN much more expensive But if you need to generate like a negative 60 volt bias, um the max in part will do the job as well And that is the great church