How to get regulated 5V from an unregulated power supply? - Page 1
Forum section: electronics / beginners

author: fisz
author_rank: Contributor
timestamp: July 05, 2016, 11:52:14 am
content: I need some assistance in designing a proper powering solution for my project. The project is an Arduino-like board, with a lot of WS2812B's.My power requirements are about 4A of current at 5V, where 500mA is for the electronics (processor and other misc. equipment), and 3.5A for the LEDs. The problem is, that the 500mA needs to be "high quality", i.e. regulated power. For the rest, I only need 5V-ish unregulated power.I have considered the following:1. Power everything from a decent plug-pack that can supply at least 4A@5V of regulated power. But these are expensive, and I only need 500mA of that. So, I figured there must be a better solution.2. Power everything from an unregulated 9V or 12V plug-pack, and then go through a step down converter that can supply 4A@5V. But again, these are expensive, and I only need to regulate 500mA. And I get a lot of power loss when I convert mains twice, once to 9V and then to 5V.3. Power everything from an unregulated 5V plug-pack (more affordable), and then "regulate" only a 500mA. But to have regulated 5V from an unregulated 5V, I need to step up the voltage well above 5V, and then step it down to my requirements. I find this idea "overcomplicated" (lots of extra parts), I assume there must be a better engineering solution to that problem (I've heard about SEPIC converters, but those are well above my skills at this point).4. Design two separate power circuits -- one for the electronics and one for the LEDs, and power them with two separate plug-packs. I would like to avoid having two cords and two power supplies.What is the best option for me?

author: Aodhan145
author_rank: Frequent Contributor
timestamp: July 05, 2016, 11:55:26 am
content: http://www.ebay.co.uk/itm/DC-5V-12V-24V-48V-Switch-Power-Supply-Adapter-Transformer-For-Led-Strip-Bulb-/182127268024?var=&hash=item2a67a190b8:m:mM9BFU5AAnM34z3iizvCIMgProbably isn't safe or well regulated but is is cheap.

author: Kilrah
author_rank: Unknown
timestamp: July 05, 2016, 12:17:02 pm
content: The best solution may be to design the power-hungry LED part to run on 9V or so (e.g. by putting LEDs in series), use a single 9V supply and regulate it down to 5V for the part of the circuitry that needs it.But you didn't give enough details about your application to say if that's a valid approach.

author: madires
author_rank: Super Contributor
timestamp: July 05, 2016, 01:07:29 pm
content: Expensive? Really?-http://www.ebay.com/itm/DC-DC-4-38V-to-3-3V-5V-9-12V-24V-5A-Buck-Step-Down-Converter-Module-Car-Voltage-/191812014140?hash=item2ca8e3103c:g:t~MAAOSwUfNXSqh1-http://www.ebay.com/itm/MP2305-DC-DC-Buck-sent-down-Converter-Module-7-20V-12V-19v-to-5V-2A-CAR-/171973556009?hash=item280a6c3729:g:hAIAAOSw5ZBWJUj2Use the 5A converter for the LEDs and the 2A converter plus a LC filter for the controller board. Power both with an old laptop PSU or whatever you got. Those DC/DC converter boards are cheaper than buying just the buck converter chip from a known reseller/distributor.

author: gblades
author_rank: Contributor
timestamp: July 05, 2016, 01:18:11 pm
content: As Aodhan145 said that sort of power supply is probably your best bet. The other alternative is if you can get hold of an old PC power supply from somewhere. New they are more expensive but you can often pick up an old dead PC where the power supply still works.@Kilrah the WS2812 is a 3 color LED with the controlling chip on board so requires a fixed 5V supply.@madires thats fine but you still need a mains power supply to get down to the 4-38V input the converter requires.

author: Paul Price
author_rank: Super Contributor
timestamp: July 05, 2016, 01:43:17 pm
content: Just use the simple circuit below and one power supply.

author: Kilrah
author_rank: Unknown
timestamp: July 05, 2016, 02:13:54 pm
content: Quote from: gblades on July 05, 2016, 01:18:11 pmAh yeah, missed the bit about the WS2812...Quote from: Paul Price on July 05, 2016, 01:43:17 pmThis option which is what I suggested isn't viable for the reason above then, the LEDs need 5V too, not 9.

author: MosherIV
author_rank: Super Contributor
timestamp: July 05, 2016, 04:34:13 pm
content: HiCost seems to be an issue, so this solution requires a cheap unregulated psu 7-9V capable of 4ANow use this voltage regulator circuit:http://www.electronicspoint.com/attachments/7805-passq-jpg.4809/The circuit uses the 7805 to generate a reference 5V, the transistor is in emitter follower configuration and will output the voltage on its base. You can use any 7805 because the transistor passes all the current. The transistor MUST be heat sinked since it is now acting as the voltage regulator.The 2n3055 is a well known power transistor, capable of upto 15A depending on the version you get.The circuit does not show the stablising capacitors needed around the 7805, they are a must!

author: mariush
author_rank: Super Contributor
timestamp: July 05, 2016, 05:11:24 pm
content: So you're looking at around 20 watts, which means your power supply would have to be capable of about 25w (to account for efficiency losses when converting from higher voltage to lower voltages)7.5v , 9v wall adapters would be expensive at the currents that would be needed (3A or more), it would be cheaper to go with laptop adapter style power supplies. You may be able to get 12v adapters (which were commonly used to power some LCD monitors) or 16.5-19v laptop adapters which can output safely 40w+ and they're cheap.You could use a simple switching regulator IC capable of 4A+ to output something like 5.2-5.3v which will be tolerated by those led strips (the voltage will drop anyway as you go along the strip) and then use a very efficient LDO to output 5v out of those 5.2-5.3v for your microcontroller (there are ldos that only need 50mV or more above the output to work perfectly fine).Here's some examples of cheap and good dc regulator ics, just from a brief look on Digikey :AOZ1294PI :http://www.digikey.com/product-detail/en/alpha-omega-semiconductor-inc/AOZ1284PI/785-1689-1-ND/4900905TPS54531 :http://www.digikey.com/product-detail/en/texas-instruments/TPS54531DDAR/296-40801-1-ND/5178678Sanken NR111D (DIP package) :http://www.digikey.com/product-detail/en/sanken/NR111D/NR111D-ND/4289389Sanken SI-8050HFE (to-220, 5.5a max) :http://www.digikey.com/product-detail/en/sanken/SI-8050HFE/SI-8050HFE-ND/4175639Sanken SI-8008HD (TO-263-5) :http://www.digikey.com/product-detail/en/sanken/SI-8008HD-TL/SI-8008HD-TLCT-ND/4175674These are all capable of 18v or more, if you're willing to go below 18v maximum input voltage there's quite a few more good chips

author: madires
author_rank: Super Contributor
timestamp: July 05, 2016, 05:18:05 pm
content: There are better high current circuits in the 78xx datasheet. Based on the required power dissipation most PSU circuits with a 2N3055 won't go beyond 5A usually. For the suggested 9V input the 2N3055 would have to dissipate (9V-5V)*4A = 16W. Maybe a 1.5K/W heatsink?

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 06, 2016, 10:12:26 am
content: Quote from: Aodhan145 on July 05, 2016, 11:55:26 am+1. if you need more compact you can put 2 of these (following link) into your project. 10pcs will get you as costly as 3pcs of the above...http://www.ebay.com.my/itm/10PCS-Super-mini-3A-DC-DC-Converter-Step-Down-Power-Supply-Module-3V-5V-16V-/201414945974?hash=item2ee5442cb6:g:kJQAAOxyXVBSL~xabut on the con side, reallyyyy con. when this thing (and i guess any smps based module) fails, it tends to spit anything on the input to the output, damaging your logic circuits. the safer way is adding post linear regulator like the 7805 above. when pre-regulated smps failed, all heat will be taken by 7805, but when 7805 (and i guess any linear based regulator chips) fails it will tend to disconnect (open) the output from the input.

author: fisz
author_rank: Contributor
timestamp: July 07, 2016, 09:21:00 am
content: Thanks to all of your ideas. It seems that I put too much weight on the "cost" argument. What I really meant in my first option is that using a 4A power supply is unnecessary (its like having a trailer truck to transport something when you really need just a forklift -- you pay to much).And, since I do this project just for learning (and fun, obviously), I'd rather not choose the easiest solutions