Can I get 5V 2.5A from a 12V 1.5A power brick? - Page 1
Forum section: electronics / beginners

author: technix
author_rank: Super Contributor
timestamp: August 15, 2018, 06:04:49 pm
content: The power brick is rated for 12V 1.5A, or 18W. The 5V 2.5A (12.5W) is intended for a NeoPixel LED strip, in its a worst case scenario (maximum brightness on all LEDs.)Can I get 5V 2.5A from that power brick using a single-phase 3A-rated buck converter (e.g.TPS563201and an appropriately-sized inductor,) or can I use a two-phase converter with two 2A output phases (e.g.MP2122with its two output phases in parallel,) or do I need a bigger power brick?

author: metrologist
author_rank: Super Contributor
timestamp: August 15, 2018, 08:15:40 pm
content: You would look at the conversion efficiency and power capability of the buck converter.You need 70% conversion efficiency with 2.5A continuous duty, minimum.

author: technix
author_rank: Super Contributor
timestamp: August 15, 2018, 08:47:49 pm
content: Quote from: metrologist on August 15, 2018, 08:15:40 pmBoth chips are no less than 80% efficient at all loads. With that in mind, will a single-phase buck converter work, or do I need a two-phase one?

author: metrologist
author_rank: Super Contributor
timestamp: August 15, 2018, 09:02:31 pm
content: Either type should work as long as it can handle the load.One of your chips is rated 2A, so not enough. Also:Continuous Power Dissipation (TA = +25°C) (2) ................................................................. 1.25WIf you are running 12.5W out at 90% efficiency, that is about 14W in and 1.4W dissipated.That chip will not last.Here is some info about multiple phase converters:http://www.ti.com/lit/an/slyt449/slyt449.pdfhttps://www.electronicdesign.com/power/supply-meets-demand-use-multiphase-converters-solve-tough-power-design-challenges

author: james_s
author_rank: Super Contributor
timestamp: August 15, 2018, 09:15:04 pm
content: I would expect this to be fine. It should tolerate being run full brightness continuously even, but in practice you will likely have plenty of margin.

author: technix
author_rank: Super Contributor
timestamp: August 15, 2018, 09:27:29 pm
content: Quote from: metrologist on August 15, 2018, 09:02:31 pmThe 2A chip is rated 2A each phase. Should I be using that chip it would be two phases in parallel for a possible 4A maximum current.

author: metrologist
author_rank: Super Contributor
timestamp: August 15, 2018, 09:28:33 pm
content: Quote from: james_s on August 15, 2018, 09:15:04 pmWell, I didn't really look at everything, but he wants to power from a 12V brick? Will that still work?Wide 2.7V-to-6V Operating Input RangeIf one channel is 2A and he wants 2.5A, can he use those channels in parallel?

author: ogden
author_rank: Super Contributor
timestamp: August 15, 2018, 09:45:58 pm
content: Multiphase converter would be overkill for 5V 2.5A. Just properly size yoursynchronousconverter IC. Obviously as already noted, sot23 is way too smallTPS54427seems to be matching your requirements. Do not forget to check board layout & docs of evaluation module, SLVU579.

author: james_s
author_rank: Super Contributor
timestamp: August 16, 2018, 01:21:09 am
content: I bought a bag of those KIS3R33 modules some years back that I use for this sort of thing. I don't know what they came from but there seemed to be huge quantities of them surplus in China, pulls from something or other. There are loads of other buck regulator modules out there that will do the same thing if you don't feel like designing something yourself.

author: Zero999
author_rank: Super Contributor
timestamp: August 16, 2018, 01:44:42 pm
content: Why not simply use a 5V 2.5A brick? That's got to be the easiest solution.Is there a requirement for 12V? If so, what current? Then the question is whether it's better to use a 5V brick and boost to 12V.If only 5V 2.5A is required, then use a 5V brick. Converting 12V to 5V, when it's not necessary is bad design.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 16, 2018, 02:49:45 pm
content: Quote from: Hero999 on August 16, 2018, 01:44:42 pmUnless you have any significant cable length. Local conversion at the load end both reduces losses and gives you tolerance of voltage drop.

author: Zero999
author_rank: Super Contributor
timestamp: August 16, 2018, 03:12:02 pm
content: Quote from: mikeselectricstuff on August 16, 2018, 02:49:45 pmThat's true, but wouldn't it make sense to use an even higher voltage in that case?I suppose 12V might be more optimal, because a simple buck converter can convert 12V to 5V more efficiently, than 24V to 5V.

author: james_s
author_rank: Super Contributor
timestamp: August 16, 2018, 05:13:17 pm
content: It would also make sense if you happen to have some nice 12V power supplies already, or if something else you also want to power requires 12V.

author: Zero999
author_rank: Super Contributor
timestamp: August 16, 2018, 07:55:14 pm
content: Quote from: james_s on August 16, 2018, 05:13:17 pmThat's what I was thinking, but would disagree with it being a good reason for this. It will probably not cost much to buy the correct power supply and save the 12V ones for another project. In the past I've made some poor design choices because I resorted to using what's available, rather than being more patient and ordering the correct part. Fair enough, the part is expensive or takes too long to get, then it makes sense, otherwise it's generally better to wait and spend a little.QuoteThat makes more sense, but if the 12V device is small, compared to the 5V device, it begins to make more sense to use a 5V PSU and a boost converter. Of course this is assuming the cable length is short, otherwise it's better to transmit the power at a higher voltage, though a long cable, as previously mentioned.

author: technix
author_rank: Super Contributor
timestamp: August 17, 2018, 05:00:15 am
content: Quote from: Hero999 on August 16, 2018, 01:44:42 pmQuote from: james_s on August 16, 2018, 05:13:17 pmI just happen to have a bunch of 12V 1.5A and 12V 2A power bricks in spare.Here in Shanghai those are handed out as part of standard telecommunication hardware from China Telecom, but those field service engineers just never bothered to collect them when returning devices for upgrades or repairs, allowing them to accumulate here.Quote from: james_s on August 16, 2018, 05:13:17 pmThere is nothing that requires 12V in this LED strip.Quote from: mikeselectricstuff on August 16, 2018, 02:49:45 pmIs 1.5 meters to 2 meters a significant cable length? The copper might be thin though, being Chinese-made el cheapos.

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 17, 2018, 05:04:59 am
content: You could measure the wire resistance and calculate the expected drop.

author: digsys
author_rank: Unknown
timestamp: August 17, 2018, 06:07:48 am
content: Unless you want to go to the trouble ofrollingyour own, something like the TI PTN78060W is perfect. 3A, high efficiency.Actually designing them in right now :-) into a few projects. Just add a couple caps and a Vset resistor.

author: Zero999
author_rank: Super Contributor
timestamp: August 17, 2018, 07:46:39 am
content: You'll probably find building a 12V to 5V converter will cost as much or more, than the correct power supply in the first place. You might be able to save a tiny amount by purchasing a 12V to 5V ready made module, but that's just penny pinching.

author: technix
author_rank: Super Contributor
timestamp: August 17, 2018, 07:50:12 am
content: Quote from: digsys on August 17, 2018, 06:07:48 amCurrently it is choosing between a single-phase SGM6130 based design or go with a M1VRv2-2DX2 software-defined multi-phase converter design.

author: technix
author_rank: Super Contributor
timestamp: August 17, 2018, 07:56:54 am
content: Quote from: Hero999 on August 17, 2018, 07:46:39 amI need to build a MCU board for the NeoPixel strip anyway, so this power module is simply piggybacking. No significant cost occurred with or without that power module.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 17, 2018, 11:27:48 am
content: Quote from: Hero999 on August 16, 2018, 03:12:02 pmYes - 24V would be my default choice, and there are plenty of converters that would do it. However for intermediate cable lengths, it may be that local regulation is the primary concern rather than efficiency, and 12V may be easier to get - e.g. plug-in and desktop type PSUs are less common at 24v, though 19v laptop supplies are another common option.Once you go over 24v, thinks like circuit protection and PSU availability become more of an issue, so you'd only go that way if you had a particular need for it.