Can I clean a USB 5V power source using a buck-boost converter? - Page 1
Forum section: electronics / beginners

author: Marmotta
author_rank: Contributor
timestamp: March 02, 2024, 11:34:57 pm
content: I have a couple of projects that require a 5V input which I'd be supplying via USB-C. As I intend on selling my project in small batches without power supplies, I thought it would be best to add some power circuitry to clean the 5V signal as I don't know what quality power supplies will be used in each case. I was thinking of using a TI TPS63070 buck-boost converter, but was wondering if it would be possible to have both the input and output voltages of a buck-booster converter be the same value? Would it be preferable to use a cheaper boost converter and an LDO?Alternatively, am I going about this the wrong way and is there a preferable method to achieve what I want to do?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 03, 2024, 04:54:38 am
content: What are you doing with it?USB, within tolerance, isn't particularly objectionable; a modest bypass cap, with ESR, and maybe a TVS, is most all I would bother with.I would be more concerned about other aspects of your circuit if it's inviting extra noise -- like poor CMRR or ground-loop of an audio circuit for example (use op-amps with reasonable PSRR, bias to mid-rail to maximize dynamic range, use differential input and output arrangements to break ground loops). If it's a digital circuit, an LDO to 3.3V covers a lot of cases. Up to you whether that's practical/feasible.You might also simply warn users that non-compliant power sources may damage your device.Tim

author: Marmotta
author_rank: Contributor
timestamp: March 03, 2024, 11:03:28 am
content: Thanks for the reply! In both cases I'm using USB to power retro gaming consoles. They can run on 5V and between 1-2A, but originally would come with a 9-12V AC adapter and then use an LM7805 and caps inside the console to obtain the 5V.I don't think my circuitry would invite any additional noise, as it's going to be a pretty minimal board and if it was just something I was working on for my own use, I probably wouldn't have bothered with any protection circuitry.Do you reckon something like this circuit I've quickly drawn up would work fine in this use case?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 03, 2024, 11:41:31 am
content: Well, if you're thinking S/NES, you need a boost regulator anyway; potentially isolation as well, if the supply is common-ground -- as might be the case if one plugs it into a PC or hub, though those don't usually have 2A+ available as an adaptor does. You may want to recommend use with adapters only, and specific units at that (for EMC purposes).That is, unless you're also hacking the console to remove the input FWB (when applicable), and resolve any high-voltage loads; IIRC the NES uses +10V for the video circuits (not sure about SNES but probably too?), so merely cleaned-up 5V won't do. Noise might affect audio quality, video banding, etc., so some filtering may be desirable here, and don't ignore common-mode filtering, preferably test EMC.Adapters should generally be isolated and non-grounded so that's fine, but put that on the list of things to check/verify about selected parts.Note that, even with nominally-coaxial cables coming off the thing (RCA cables, RF if used), especially cheap RCA cables use loosely shielded wires, spiral wound rather than woven ground for example, which have essentially no RF immunity, and, while it would be nice if AV equipment were well enough shielded, or filtered, or designed, to reject RFI, but often they're not, and pick up very-nearby FM radio, or cellphone noise, or... So, keeping CM noise / RFI low from the power supply is pretty important.Tim

author: Marmotta
author_rank: Contributor
timestamp: March 03, 2024, 06:59:56 pm
content: Close with the NES, but it's a Famicom. Everything is going to be internal and from what I can tell the 9-10V voltage that it generally expects goes through a choke and capacitor, then straight to the power switch at the front of the board and back to the LM7805, so as far as I can tell everything on the board runs off 5V.I've removed the existing circuitry, printed a 3D bracket and mocked up how the USB-C port would be installed with ideally minimal circuitry as mentioned.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 03, 2024, 08:58:24 pm
content: Ah... modified indeed. Then, filtering probably isn't a bad idea, and I wouldn't worry about post-regulating it as everything should be fine on 4.5-5.5V (TTL / NMOS? logic, and CD4000 CMOS). An adapter shouldn't be particularly noisy at low frequencies, with a consistent load attached, but you might want to try a few if the first one you try is noisy.Adding a converter stage is almost certainly overkill, but would have the advantage of more accurate 5V output, and can clean up more/poorer adapters (running in burst mode, having subharmonic oscillation, or poor compensation; or poor PSRR, including single-stage APFC types if that's even a thing). You'll probably need a bit more board area to do that plus requisite filtering.Tim

author: langwadt
author_rank: Super Contributor
timestamp: March 03, 2024, 09:06:43 pm
content: https://www.ebay.co.uk/itm/375046754293set for 9V and done?