Hi, it's time for another installment in the Power Supply series. And yes, it's another revision. Schematic: I Got some changes. Not surprising because when you work on these projects long enough, one thing leads to another, you start thinking things and you start refining it and you get caught in that trap of well, maybe I can reduce the cost.

Oh, maybe that idea I had at the start wasn't that great or I've changed my mind I think this is more important now and well, one thing leads to another: you a whole raft of changes. So not only do I have rev C schematic here I'll go through it in detail and all the changes to it, but I'll talk about the system engineering aspects to it as well as well as revealing I Guess the big secret to what my original intention for this lab power supply is. Let's go now. when it comes to lab power supplies like these, what do they all have in common? Well, they're all big.

They sit on your bench like this, and they have one of these, a power cord they're tied to wherever. uh, they're tied to your bench. just like a bench multimeter for example. But I do a lot of designs I'm working on working on different part of the bench I don't want to have to move my power supply somewhere else I might be.

it might be something that's uh, portable I might be working on the floor or could be working anywhere on a different bench on the other side of lab. whatever. So I had no intention of just doing yet another bench lab power supply like this. There are dime a dozen you can buy them for next to Nyx on eBay They're so cheap and so readily available.

so I thought I'd go for something that was a bit more Niche was smaller and met a different requirement. Now please excuse the crudity of the model. it's by no means finished I haven't done the front panel. it's all just sort of hanging there I haven't put and put the uh uh The Binding post on the front, but this is the case that I originally intended to house my power supply in and I looks like I'm still going to do that.

and what's the? There's two cool things about this one. It's very small look, it's only the size of my hand. It's tiny so it's very portable. You can take it to wherever you need the job.

and what's the next big thing about it? I'm glad you asked. Well Taada, My original intention was to have it battery powered lithium ion batteries I was going to have 3 18650 lithium ion batteries inside this thing. It's a rechargeable bench power supply. Is it a world first? Oh I doubt it.

but I don't know offhand of any other uh, rechargeable, just general purpose lab power supply on the market. So I thought it'd be quite unique to actually have a little battery powered power supply like this. and hence why yeah, people have always been asking from the first video why it's not 30 volts at 3 amps and 100 wats and all this sort of stuff. This is why I wanted it to be small compact battery powered for a good majority of the designs I work on these days are only drawing a wat or two, you know, tops.

I don't need a 30 volt 3 amp power supply and if I do I've already got a bunch of those sitting on my bench I Just wanted this thing. small portable battery powered recharge ible Beautiful! So the need to have this thing battery powered from a couple of lithium ion batteries in a small case is what drove most of the design decisions from the start. I Started out by thinking right I want a battery powered power supply I went around I want it small house a couple of 18650 batteries, a small LCD some uh, you know, a couple of knobs and a couple of switches and that's about it. So I went around searching for a case for that and this one's pretty ideal and I'll show you why in a minute.

but this also leads into uh, why I've changed the design in uh rev C now my third uh variation of this design I've actually changed, uh, a few things. The look and feel is going to be very similar, but ah, the stuff like the heat sink on the back and the accessibility of the connectors and stuff like that really uh, drove this uh rev C design decisions. Now as for the case itself, it's a um Hamond SL Well, it's actually a Ritech but I think Hammond actually uh, redo these now and it's an RM 205m and good thing. couple of good things about it that I like a it's pretty low cost, it's it's less than $4 uh in volume for this size and uh, the uh.

three things. Actually low cost. uh and it has standard uh mounting holes on the top and bottom side of the case like this so you can mount boards on both the top and the bottom of it. and I thought that was really good because I chose a heat sink which is kind of low profile like that and by the time you get that second one on, you've actually got some height there available to maybe put a couple of extra switches or something else along the top.

And of course my original intention was actually um to have these batteries actually uh mounted on a second board on the top here with its own battery charger. hence why in my previous designs I haven't included um, any battery charging circuitry on the board I just had this header connector over here which I was going to connect up to the top uh battery board which houses those batteries but I've uh changed my uh mind on that so we'll go into that um at a later stage so you can mount dual Pcbs on there and by the way, they're exactly the same uh footprint. So um, one of the neat things is is if this board mounts on here, there's my four mounting holes on there. Not only can I mount it on, well, let's call this the bottom of the uh case.

Yeah, it essentially is. um, but I can actually flip it over like this and mount it on the top upside down like so so that the board, the main board's actually on the top and the knobs are on the top of the case. Why is that important? Well glad you asked because if you've got it down like this, it's a very compact case. so I haven't got much room at all and I was going.

the LCD takes up all this space over here cuz it's pretty big. I wanted to be able to see the LCD from the other side of the room or you know, from a reasonable distance. So I've got my uh binding post at the top here and that's a bit. that's you know it's not that great.

These knobs are on the bottom and you've got to try and adjust the knob with your wires coming out from your binding post. Well, to solve that, you can just stick the board upside down in this case and Bingo! you've now got your binding posts on the bottom of the case like this so your wires come out and your knobs and your switches are on top so they don't get in your way of your wiring. It's pretty neat versatile case I Really like it and one of the things I really love about this case. in fact Hammond cases in general is that look at the data sheet here it is the RM 2015m and check out the awesome interactive 3D model of the case which you can download as well.

Great if your Uh CAD package PCB CAD package supports 3D models. You can import these and you can see if your boards fit and things fit on your front panel and it's just it's beautiful I Love it and you can actually um, interact with the thing and not only rotate it around like this which is brilliant but you can actually select individual parts of it like this and this is uh and you can can do all sorts of other interactive stuff and this is all with inside the PDF data sheet. Brilliant! Why can't every manufacturer do that? It really just makes you want to choose their cases just for the cool data sheet. But a third thing that makes this really cool is that this is a 50 mm High case.

It's available in a shorter version 30 mm, High 50 and also 70 and here and this is what it looks like so it's actually a bigger. The whole are exactly the same. Footprints are directly compatible like that, so you can actually put it in a bigger, beefier case like that. I love it.

and then you don't have to change your PCB design. If you need more room in the case for something for some custom mod or something like that, you can put it in this case. but um, although this case I think is a bit too big I mean it just looks a bit. you looks a bit tall and bulky and stuff like that.

So I think my goal is to get it into this smaller size case like this and try and get the LCD and The Binding posts and everything in there plus all the connectors on the back and the ethernet and power and other stuff on the back. So let's take a look at it. So this is my Revb board. Uh, as you've seen this before, I've done some uh, troubleshooting on this thing and I was thinking about it and looking at the big heat sink on the back.

there are a couple of things I was looking at a the big heat sink on the back I couldn't access um ethernet I'd have to if I wanted that ethernet uh module which I was talking about sticking it in the middle of the board here somewhere or having it, um, somewhere else in the board, maybe on the top, uh Board of the case, then really, there's nowhere to put it cuz it's fing with one of the mounting holes there. it's not nice I can move it over, but then there's no room for the DC input uh charging Jack or originally I was going to have a USB uh charging jacket. it actually uh, charge up from either a DC jack or 5V USB as well. but I think I'll just uh, stick with the standard Jack which we'll go into now.

So I thought ah, you know there's a big heat sink on the back and it costs about four bucks or something in volume. The heat sink is not cheap, so I was looking at, you know the price was creeping up I was looking at maybe trying to shave some cost off and I thought well oh gee, a couple of things led to it. Okay, one was the price of the Uh heat sink and the size and the accessibility of the connectors on the back. So if I could get rid of that heat sink then well I can save some cost and get room for the ethernet Uh module there and and other stuff on the back so that would be really nice.

save some cost, get some room. beautiful but I'd have to change it to a switch mode design which we'll go into but I decided no I'll just keep my um LT uh 3080 as we've got. and the other thing um is I was going to charge it from 38 650 lithium ion batteries and once you go to three of these or four, even the Uh charging solutions for those become more complex and more expensive and more difficult and things like that. So and really, it was taking up a fair bit of uh room inside this thing I couldn't Mount them in the other uh orientation if I wanted to.

and really with a linear power supply I was using here, you're really pissing away a lot of your capacity in your battery due to your linear uh voltage regulator. So you know if you've got 12 volts coming from your Uh batteries for example, then well and you're only putting 3.3 volts um out. Uh, which might be a typical Uh power for a project or something like that. there a lot of power wastage in your heat sink just throwing it away down the drain.

can't have that. So I decided to go to two uh, lithium Ion 18 650 batteries I can mount them in other orientations, ditch the top board on the top uh, put in the battery charging circuitry onto the main board so all I've got to do is have a connector coming off, going to the battery pack and getting rid of the heat sink by actually having a switchin pre-regulator Beautiful! And the other thing was the LCD I was originally going to have like a ribbon cable and there's my LCD connector there. I was actually going to have it. um, you know, ribbon cable coming out to the front of the board and really, you know it's then there's no way to mount this.

um on the front panel. it have to be glued in place or something ugly like that. So I decided Well I'm redesigning the board anyway. So why not? Actually because this is a PCB Mount um uh LCD it's got the RGB leads on the side plus the pins there.

it'll Mount directly on a board. I might as well go back to the original intention I had before I got the ribbon cable uh before I sort of of uh, relented and went for a ribbon cable is to have just a vertical PCB coming out of here like this and and that would actually hold the LCD in place just in front of the front panel. But to do that of course I didn't have room for it before because I had the 5vol USB on the front. but aha, if I was getting rid of this heat sink on the back then I couldn't have this.

uh, couldn't really have this 5V voltage regulator anymore. So I decided ah, buger that I'll just get rid of the 5V output completely and that gives me room just behind the switches on the front panel there to actually put a vertical Riser board to hold my LCD in place. So I think that's a a more elegant design I've dropped the 5 Vols but I think I've gained it in terms of uh, just nice um, build functionality and mounting the LCD And and if you're wondering what the deal is here with the Uh heat sink sticking out the back like this and I've actually designed my board to poke out the back like that it's done so that the back panel here would slide just behind it would have actual Uh cutouts for the two voltage regulators and that back panel there would just slide directly out there so it just isolates the heat from the inside and keeps it on the outside like that while you got the plastic rear panel that just slides into those slots over there like that. So I'm going to replace uh that because I'm getting rid of this I still need some heat sinking even though we're going to have a switching pre-regulator on this thing.

I'm just going to have the Lt380 directly on an aluminium, a flat aluminium back panel. easy.