12v to 5v voltage regulator questions

[mattie47]

Hi all,

I'm hoping someone might be able to give me some suggestions for something I'm trying to design in easyeda and get through lcsc and jlcpcb.

For reference, my background isn't electrical engineering, and I've spent many many hours researching the power aspects of my project and understanding things like linear regulators verses switching, requirements, and constraints of different options. Being a test engineer, I'm trying to consider all factors which could impact things before making a decision.

In short, I'm trying to build a pcb with an arduino (specifically this one - https://robotdyn.com/mcu-pro-mega-2560-atmega2560-16au-usb-ch340c-with-pinheaders-2-lines-pinheaders-pitch-0-1.html) and numerous modules/peripherals attached to it. I'm avoiding powering any 5v modules from the Arduino and instead power those components from the 5v regulator. This is because the arduino itself operates at 200mA (according to the datasheet) and the manufacturer recommends only 7-9v on VIN otherwise its onboard AMS1117s can get too hot. Because I *do* want to provide 12v to the VIN of it, I'm avoiding having any other components connected requiring the Arduino's onboard regulator.


Essentially my requirements are a voltage regulator (and 5v rail design) that:
- Can go from 12v to 5v
- Safely provide 500mA output
- Simple
- Can get parts through lcsc.com. Ideally "basic" parts for JLCPCB. 
- Has circuit protection e.g. Schottky diodes protecting reverse current, over current protection etc.

So - What have I considered?

Linear Regulators

Initially I looked at the 7805 linear regulator since this is super popular, common, and only requires a couple caps to implement.

My concern however is the fact it's linear and converts excess voltage to heat. Given potential output requirements, I'm concerned this would generate far too much heat, and I don't want to add a heatsink - (input voltage - output voltage) * current. Overall it just seems inefficient.

So this lead me into looking at various switching regulators, followed by LDOs...

Switching Regulators

For those changing out a part such as the 7805 for a SR, I see the general recommendation is something like the OKI-78SR-5/1.5-W36-C. While this is fine if you're getting parts from mouser or element14, I'm trying to get everything from lcsc which doesn't appear to have something like this. Even if they did, I'm creating something "new" and would have only gone for this because it's a drop in replacement for the simple 7800 series LR.

I then started looking at some other components such as the LM2596.

Even better, someone has already designed a schematic and PCB using it which I might be able to use as a reference https://easyeda.com/wagiminator/y-lm2596-5vbuckconverter-smd

However this got me thinking - Given I'm just powering a 5v rail with numerous components, is this overkill considering devices like LDOs? Or should I just call it a day and use this schematic + datasheet as a reference?

Secondly, some of the connected peripherals are potentiometers used as dials for controlling the Arduino, and I know SRs generate noise which could impact things on the analogue GPIOs.

LDO Regulators

Low-dropout regulators seem to be a really logical conclusion here, but I don't really know what to pick from LCSC or a reference schematic for what I may need.

As per the wikipedia page for them (https://en.wikipedia.org/wiki/Low-dropout_regulator), they:

include the absence of switching noise (as no switching takes place), smaller device size (as neither large inductors nor transformers are needed), and greater design simplicity (usually consists of a reference, an amplifier, and a pass element). The disadvantage is that, unlike switching regulators, linear DC regulators must dissipate power, and thus heat, across the regulation device in order to regulate the output voltage

So yes, we're back to heat dissipation, however these seem to be a better option than the LR7805. I assume there's a "safe" 500mA option for 12v to 5v, but I don't really know where to begin with looking.

So what do you all think I should do?

If you think LDO, I'd love lcsc part recommendations and schematic :-)

Thanks a lot!

Matt

[msat]

Hey mattie47

So, LDOs are linear regulators, with the main difference being that they can output a voltage closer to the input voltage compared to non-LDOs. Since you're talking about stepping down to 5V from 12, then there's no real good reason to use one.

For efficiency/heat reasons, a switch mode bucking converter is probably ideal. You can buy drop-in modules from a lot of sources, probably including lcsc. What is the source of your electricity? If it's batteries, then anything other than a DC-DC converter is going to waste over 50% of your power.

200mA for an Arduino? Maybe at everything  going full-tilt, including pins sourcing max current.

12 to 5V is quite a voltage drop. Another common thing to do is to use an intermediary regulator as well, so for example, 12V in-> 9v linear regulator -> 5v linear regulator. That way, power dissipation is spread across multiple regulators. Similarly, you can put dedicated regulators on each of your modules, so you're not just using one to power everything.

[bob91343]

This seems like overthinking.  It's a simple thing.  You need 5V, put in a regulator.  There are regulators rated for more current than the usual 7805.  The best idea is to put in anything that works and critique it later.  If you need low noise, either use a linear unit or put in some filtering.

You need to weigh factors such as cost, board space, heat management, assembly time, etc.  It's not worth it for something as basic as a power supply regulator.

[JustMeHere]

Since you're new, just find a linear 5v regulator that max input is over 15v.   LDO probably isn't the right place to start.  They tend to be low power too.

Look around SparkFun and AdaFruit for ideas.

[mattie47]

Hey msat,

Thanks for your response.

>So, LDOs are linear regulators, with the main difference being that they can output a voltage closer to the input voltage compared to non-LDOs. Since you're talking about stepping down to 5V from 12, then there's no real good reason to use one.

Primary motivation for LDO was small footprint, and what looked pretty simple to put in a circuit for a beginner. I guess my reasoning was because I've used things like https://www.aliexpress.com/item/4001005985230.html before.


>What is the source of your electricity?

Standard 12v wall-wart dc power supply.

>200mA for an Arduino? Maybe at everything  going full-tilt, including pins sourcing max current.

Yeah I imagine you're right. I'm still waiting for the actual specific model Arduinos in the mail so haven't been able to test myself, however the 5v will be powering two relays defaulting "on" which I believe will be about 70mW each along with a few other peripherals. 

>12 to 5V is quite a voltage drop. Another common thing to do is to use an intermediary regulator as well, so for example, 12V in-> 9v linear regulator -> 5v linear regulator. That way, power dissipation is spread across multiple regulators. Similarly, you can put dedicated regulators on each of your modules, so you're not just using one to power everything.

This did cross my mind, which would mean I could power the arduino via something like LM7809, and then connect an LM7805 to that. Just not sure if that's what I should do, or persist with something like the LM2596-5.0.

I guess for some more context, I'm planning on using JST 2.0 PH connectors for a number of things like buttons, LCD screen (which will be attached to the box this goes in), so the idea was to have a common 5v rail these all connect to, with the relevant sensor pins then going to the Arduino.

Thanks,
Matt

[sleemanj]

12 to 5 is 7v, at 500ma that's 3.5W for a linear reg to dump, a fairly substantial amount of heat.  I would rule out any linear reg (ldo or otherwise) unless you will use a heatsink (or revise your current requirements).

Monolithic Power make some common buck mode chips used in china.  Eg MP1584EN

[Kjelt]

At TI.com you can create and simulate your own smps circuit but I doubt if lscs has those parts.
Which leaves you with some chinese smps ic which often only has chinese datasheets and to have trust in your final solution you have to build and test your solution which can take months.

You said you just started so I won't advise that route.

To be producing fast and reliable I would make the pcb with a standard TO-220 7805 footprint and leave room for future replacement board.
Leave it open at manufacturing and put in yourself the OKI-78SR-5 or somewhat cheaper alternative CUI Inc. VXO7805-1000.
That way you can already finish and ship products with a reliable and tested regulator while if you still want to develop your own.

For those changing out a part such as the 7805 for a SR, I see the general recommendation is something like the OKI-78SR-5/1.5-W36-C. While this is fine if you're getting parts from mouser or element14, I'm trying to get everything from lcsc which doesn't appear to have something like this. Even if they did, I'm creating something "new" and would have only gone for this because it's a drop in replacement for the simple 7800 series LR.

[Ian.M]

Yeah I imagine you're right. I'm still waiting for the actual specific model Arduinos in the mail so haven't been able to test myself, however the 5v will be powering two relays defaulting "on" which I believe will be about 70mW each along with a few other peripherals. 

Use 12V relays.  You need driver transistors anyway, so there's no reason not to, and it removes a significant load from the 5V rail.

If you are using LDOs anywhere, beware of the supply lead inductance ringing with the input capacitance if the DC jack is connected after the PSU has been switched on.   If the input capacitors are ceramic there is very little damping and the input voltage can transiently be doubled, which with a 12V supply will be well above the max. input rating of most LDOs, and is likely to blow them.  N.B. there is a LDO on your Arduino.
For a sim of the effect, see: https://www.eevblog.com/forum/projects/protecting-lm317-from-voltage-spikes/msg1316465/#msg1316465

[David Hess]

12 to 5 is 7v, at 500ma that's 3.5W for a linear reg to dump, a fairly substantial amount of heat.  I would rule out any linear reg (ldo or otherwise) unless you will use a heatsink (or revise your current requirements).

TO-220 packaged parts are limited to about 2 watts without a heatsink so a linear regulator will not be suitable for this application.

[Renate]

The next time you get in a friend's car, just pocket their USB charger plugged into the cigarette lighter.
Smash it with a hammer and take out the little board.

I use a few of these Velleman VMA 404 buck converters
I like that they have a trimpot and you can goose the output a little to make 5.000 V at the end user.

I do agree that if you're driving relays, drive them with the raw 12 V.
A 16 MHz ATmega328P by itself takes 10 mA.

[Manul]

XP Power has some cute little 3 pin bricks like TR10S05. They are also closed case and not expensive. I use linear regulators only for analog circuits if noise is important. In most other cases they are just a waste of energy, especialy for high voltage drops like in your case.

[tonyh88]

+1 for using DC-DC converter modules since you want something easy that just works. A bit more expensive but I assume this is a one off project.

Parametric search is your friend here. LCSC offers a bunch of these DC-DC converter modules under the 'Power modules' section . Just select output voltage and current requirements. Most of these DC-DC converter accept a wide supply voltage range (for  example 9-36V). Efficiency ( read power dissipation here) will vary depending on the input voltage and load current but that is not something to be too concerned about on a simple low current design like that if you use a high efficiency converter

Here is the lcsc link: https://lcsc.com/products/Power-Modules_634.html

[tonyh88]

Please note that some of those LCSC brands are not well known at least not where I am so I might not use these in a high reliability project.

XP-Power,Murata,Recom,TDK are allexamples of brands that are a bit more well known.

Doesn't mean the unheard off ones are not good

same kind of parametric search but on Digi-Key : https://www.digikey.ca/en/products/filter/dc-dc-converters/922?s=N4IgjCBcpgrATLKoDGUBmBDANgZwKYA0IA9lANojwAsAnGAOwQC6xADgC5QgDKHATgEsAdgHMQAX2Lx4YCNBBpIWPEVIUqIViE7cAksI75R%2BfpIkSgA

[Zero999]

You could roll your own from discrete components. Pretty noisy and not great regulation, but can be very efficient. See Roman Black's website for some ideas.
https://romanblack.com/smps/smps.htm

[bobbydazzler]

How about a buck converter as well as a 7805?  Use the buck converter to get 7v and the 7805 do the rest, this way the 5v rail would be super clean and the 7805 would only need to dissipate 1w of heat and possibly wouldn't even need a heatsink.

[Ian.M]

Unfortunately the PSRR of most linear regulators drops off quickly at high frequencies and basically sucks at and above the switching frequency of most switching regulators,  e.g. see fig 5 of the T.I. LM7805 datasheet, so you'll have a hard time getting sufficient ripple attenuation and justifying the wasted power, v.s using a high quality multi-stage passive Pi LC filter.   It *CAN* be a justifiable choice for low current supplies from the output of a cheap unregulated DC-DC converter module, but that's more for voltage stability than noise rejection.