Power supply for projects powered off USB - Page 1
Forum section: electronics / beginners

author: sean_o
author_rank: Newbie
timestamp: September 27, 2020, 05:00:15 pm
content: I want to design myself a little power supply board to power various projects I am working on. Initially I was just going to do a buck design from a 9v battery down to 3v3. But then I was thinking I might as well give myself a number of different voltages, because it will be a good leaning experience.So now, I want to the input voltage to come from a USB connection. I will still have the 3v3 supply, but now I am thinking I will add in a 5v and a 12v supply too. My plan is to use the MC34063 regulator. However, I am not sure about the 5v supply, and that is my question here. I am thinking I would like each voltage to be able to supply 100mA.Since USB is at 5v, I don't think I need to run that through any sort of regulator, but I am not sure how I can get the right current I want. Also, would I need to do anything with the voltage from the USB, or in theory could it just be fed right through to the output? I don't know why, but it doesn't ...feel, like I should just feed that right to the output.As a final thought, since I would be working with a UBS connection to my computer, is there any protection I should build in? I don't want to do something stupid and fry my laptop.Please forgive any stupid questions here, as I said, I have never designed theses things before, and am looking at this as a learning exercise (as well as something practical I can build), so any advice is welcome.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 27, 2020, 06:13:36 pm
content: I would not recommend this.I'd think your Laptop would be too valuable to be abusing in such ways with dodgy circuits. There is a real chance of damaging the USB ports of your laptop when tinkering about in such ways.For a beginner it would be far simpler to use some extra batteries, and add a buck converter to that.9V batteries are pretty small, you may consider a few Li-Ion 18650's in a box with some decent protection circuitry. If you're worried about fire hazards, put the whole thing in a metal box. Some kind of cookie jar for example.If you really want to go the laptop way, then consider adding an extra (preferably powered) USB hub. Then when something goes wrong there is a good chance you blow the HUB, and the HUB short circuits the USB port, protecting your Laptop from further damage. Don't use the cheapest hub you can find, these generally lack all protection.

author: sean_o
author_rank: Newbie
timestamp: September 27, 2020, 08:31:52 pm
content: Quote from: Doctorandus_P on September 27, 2020, 06:13:36 pmYes, this is would I would be very much concerned about.QuoteI think you may be right. That was my initial plan, but then I thought it would be interesting to do it from a USB.Out of interest, is there protection circuitry one would use when working with USB to prevent bricking something on your laptop?Thanks for the advice too, it's appreciated.

author: radiolistener
author_rank: Super Contributor
timestamp: September 27, 2020, 08:41:10 pm
content: KORAD 3005D will be enough for your project and also for your future projects

author: MosherIV
author_rank: Super Contributor
timestamp: September 28, 2020, 08:01:56 am
content: What about using/getting a powered usb hub, that way you can still do what you planned but not risk your laptop.Also have a look at usb C. It can actually supply different voltages. However, it requires usb protocol negociation to get those voltages.

author: sean_o
author_rank: Newbie
timestamp: September 28, 2020, 08:53:43 am
content: Yes, this was mentioned by Doctorandus_P.It might be something I will look at, but maybe it makes a bit more sense at the minute to get my design right working off batteries, than as some extra work I can add the USB element it.I will definitely use a hub though.

author: rstofer
author_rank: Super Contributor
timestamp: September 28, 2020, 08:23:49 pm
content: These PowerBRICKS are pretty cool for breadboarding:https://store.digilentinc.com/powerbricks-breadboardable-dual-output-usb-power-supplies/Note that they make both a positive and negative voltage.I also have several of these and they provide 3.3V and 5V directly to the rails of a breadboard:https://components101.com/modules/5v-mb102-breadboard-power-supply-moduleI would still feed any of them from a powered hub. In fact, all of my projects go through a hub, the PCs are far too expensive.

author: Rick Law
author_rank: Super Contributor
timestamp: September 30, 2020, 05:19:39 am
content: I personally would not put a laptop's usb as power source. It adds too much complication and risk.The MC34063 you plan to use can buck or boost. You are much better off bucking than boosting. Bucking is more efficient than boosting so your board will run a lot cooler and you can get more power out of it as well.If you get a 14V power brick, you can buck it down to 3.3v, 5v, or 12v.And then there is always the trick of boost+buck. You run two boards, the first MC34063 boost it to 14V, the second one bucks it down to 3.3, 5, or 12. Now you can use any power brick from 3v to the max MC34063 can take.Personally, if I need output in only those three values, I would go for a linear regulator. It is not like you need something unusual like 6.43V. Linear regulator at the values you seek (3.3v, 5v, 12v) are aplenty. Much easier to get nice clean power out of the linear regulators than a buck or boost (at least for someone with limited experience like myself...)