I’ve Never Been So Excited About Regulations! DIY DC-to-DC Voltage Converter Made By Certainly No Expert…

It was only a few short years ago that I texted a friend of mine in a panic because I had chipped the corner of a ceramic capacitor (probably a 103 or something like that). I had spread its little wire legs too far apart while trying to put a through hole CW transceiver kit together, and a small bit of ceramic cracked off. I sent a picture and asked if I could still use the capacitor. I had no extras, because, well, at that point in time I didn’t even really know what a capacitor was, let alone have a stash of them. I got a noncommittal “probably” back, and that was enough for me to keep trudging through the project. It never worked and I doubt the cap was to blame.

Fast forward to me whipping up a circuit this month in NI Multisim, albeit nothing particularly complicated, and running a simulation to check what currents and voltages I should expect so that I can appropriately size a resettable fuse. This is going to be a voltage regulator, or perhaps more appropriately called a DC-to-DC converter. I had introduced a breadboard version in my last blog here.

This is not a goalless mental exercise however. I specifically want to be able to use a 12V 3Ah Bioenno battery as a power supply for these breadboard projects that I am doing. This is so I can work on low power circuits without necessarily being tied to the power mains. A lot like my style as a portable ham radio operator; I guess I also like to tinker on the fly. I had simply been using a similar circuit hooked together on a breadboard. This caught the eye of another friend who expressed concern that if I shorted something, I would be facing 12 amps of unfettered current. Now, in reality, the voltage regulator (the 7800 series) limits current to about 1.5 amps according to its specs, but my set up was a bit janky, and I got to admit, this got me thinking about the risks.

I decided that this would be a great project for my first printed circuit board, and I set out to learn the basics of EasyEDA, an online PCB electronic design automation software. I redrew my schematic, this time carefully selected specific components for the final design.

Once the schematic was done, I headed over to the circuit board layout page and positioned my components. With a help of some online videos and a bit of intuition, I was finally able to pass all the internal design rule checks of the system. The actual voltage regulator circuit would be in the top half of the board, while a spot for two extra fuses and 3 extra voltage regulators would be in the bottom. This would allow the voltage to be switchable (for instance by using the 5-volt 7805, 9-volt 7809, or 15-volt 7815), and the maximum current draw to be selectable by changing the resettable PTC fuses (I ordered 100mA and 250mA hold current versions).

Once the PCB was laid out, I opened up the 3D simulator.

It sure is pretty, isn’t it? I don’t know why the capacitors were left out though…

For $14 in shipping, and a nearly zero cost for five circuit boards, I clicked “order” and JLCPCB had them shipped to me within four business days. To be honest, I cannot believe how swiftly these were produced and transported. I had also placed an order with Digikey for the few items I did not have; they took a tad bit longer to arrive.

Once I had everything, I went ahead and soldered on the bits…

Voilà!

Now lets face it. Given that this is my first ever designed and produced PCB, I had no idea what I was doing, and certainly made some mistakes. I numbered these in the header photo, so lets go through them.

1. I wrote some of my labels, such as “extra fuses” and the terminal plusses and minuses in copper instead of on the silkscreen.
2. The copper letters are not only difficult to read, JLCPCB wrote what I presume is their serial number over some of them.
3. I ended up going with female header pins for the fuses, both the ones in the circuit as well as the “extras” sockets. This is because I wanted to be able to switch the fuses out in order to change the maximum voltage of the circuit. I ordered both single header pin sockets as well as a 3-by-1s, as I was not really sure what would work. Due to the hopes of increasing mechanical stability, I chose the 3-by-1s, cut off the center “leg” since there was no through hole for it, and soldered the center socket so that it would not be mistakenly used. In the extra sockets, I had placed the components too close together on the design. A do-over would be to make sure I was actually placing the sockets on the board design and not the fuses.
4. Of all of my mistakes, this one is probably the biggest. It did not occur to me until after I ordered the PCB that I could change the width of the copper traces. I would definitely increase them in version 2.0.
5. I wanted mounting holes, but didn’t know how to do it. So I just added the tiny little extra through-holes to each corner. Ooops.
6. This is another one I learned about after the fact, although it probably has no effect on this particular PCB. I did not leave in a copper ground plane. I had no idea that I even could…but now I do.
7. And, finally seven is a lot like three. After designing the board, I decided I wanted to use a row of three female sockets instead of directly attaching the voltage regulator to the board. This is again, so I could switch various sized regulators in and out of the circuit. The thick-pinned TO-220 packaging of the voltage regulators make a too-large circle for the more delegate pins of the sockets, and thus resulted in crooked positioning in the final soldered product. So, I would redesign the board using the actual socket as the component instead of the voltage regulator.
8. And 8 is not marked, but the LED component layout is not the right shape either. It works, but it is snug.

Ok, but after all that does this darn DC-to-DC voltage converter even work?!

I attached a few wire leads to the “To circuit –>” side, black negative and red positive of course. As I did for the “To battery –>” side. Except, on the battery side, I outfitted the wire leads with Power Pole connectors, so that they would fit nicely with the Bioenno battery which comes pre-fitted with these ham radio operator favorites.

I then built a little breadboard circuit with a patriotic display of in parallel LEDS with current-limiting 1000 ohm resistors.

Ta-Dah! Like Independence Day! Or a little long-legged component disco party.

And the little LED in my PCB circuit lights up as well!

But what about the voltage? 5 volts almost on the nose. Success!

So this is my little DC-DC voltage converter PCB project. In the next iteration, aside from fixing all of the mistakes I already discussed about the PCB design, I will probably add an on-off switch, add a rheostat to limit the current, and perhaps put in a rotary dial in to select voltage regulators. Maybe even a switch to choose fuse sizes.

And even though I am already redesigning it, this has been a great experience. It does get me thinking about enclosures and 3d printing, but for the time being I plan on continuing to focus on the circuits. Or at least I’m telling myself that’s what I am going to do…

Always yours,

KM1NDY