Bad practice to use more than one voltage regulator on a PCB?

Hey gang-

Just a hobby guy when it comes to PCB creation…

In the past… I have created board that have a +5v regulator… that also feeds into a +3.3 regulator…etc…

My current project has both an SMD +5v regulator… and a +3.3v SMD regulator that is fed from the +5v regulator.

These are SMD regulators… and do not provide/allow a lot of current…

Is it bad practice to add -another- +5v regulator (fed from the V+ input directly… not connected to any other regulator on-board)??? Or should I just try to swap out my current SMD +5v regulator for a more robust one that allows more current? (LM7805 or something?)

Not asking HOW to do this in EAGLE… just talking best practice? or what is acceptable over the other?

Thanks!

You can go series or parallel depending on which way makes sense in your application.

In series, the first regulator has to handle all of the current (so it gets hotter than parallel) and in parallel the low-voltage regulator has to drop all of the voltage so it get's hotter than series.

The Arduino Uno has the 5V & 3.3V regulators in series.

"By default" or at low current, I'd generally go with parallel.

We've got a board at work that's powered from 5V but there are 3.3V circuits, and the CPU runs at 1.8V. The 5V isn't regulated and the 3.3 & 1.8V regulators are in parallel, both running from 5V.

A long time ago, I remember seeing an audio preamp circuit with series regulators to improve the "noise filtering" capability of the regulators.

It's a bad idea to put two regulators in parallel, that is, have the regulators' Vin connected to each other and 5V outputs connected to each other because the regulators may not share the current evenly.

One can have two regulators if 5V output networks are isolated. This is commonly done to isolate two sub-circuits, for instance one might have a separate regulator for analog circuitry and digital circuitry to mitigate getting digital switching noise on the analog power.

For a purely digital circuit one would typically use a single higher rated component.

Other options are getting two of these and use them as daughter cards, one for 5v, one for 3.3v.

These are an option too:

https://www.ebay.ca/itm/DC-DC-1-8V-5V-to-3-3V-Step-Down-Step-Up-Converter-Wifi-Bluetooth-ESP8266-CC1101/202548332357?var=502605564632

Thanks for the reply guys!

I dont think use a buck is in option in this case.. as I'm designing the PCB and it all 'has to be on-board' (so to speak)..

Further details in case it changes anyones stance/feedback..

My current custom (all-in-one) board is basically an Arduino and Adafruit 'Waveshield' all merged into one.

I have done this before with other custom boards I have made.. and it works great.

It currently has a +5v regulator (SMD).. dont recall part# or current limits..but if I recall.. roughly 150mA or something?
it also has a +3.3v regulator.. (fed from the +5v regulator)..

For the uSD card/buffer...etc..etc...

However... on this project, I am also adding in some 5050 packaged LEDS...

My choices were/are:

Neopixels or add in an MAX7219 chip..

Pros & Cons *(as I see them)

- Neopixel approach:

  • +5v
  • no extra IC's required
  • lots of CPU required (plus waveshield stuff)
  • Neopixel set-up not tested with Waveshield requirements (might be idea killer)

- MAX72219 approach:

  • easy control over many leds
  • +5v requirement
  • current needs are low due to multiplexing of MAX7219 chip
  • No RGB like Neopixels
  • extra IC integration on PCB
  • extra routing of 'matrix' led wiring (might be idea killer)

In my mind.. the current regulators.. are -not enough- to power anything more than what I have going on.. so if I add Neopixels or the MAX7219 chip.... I was thinking adding -another- +5v regulator.. to power the MAX7219 chip (or the Neopixels)..
-OR-
Use a bigger regulator (like a LM7805 or equivalent) that supplies 1A or 2A
I'm at the point where I need to add in the '5050's' of my choice.. and any extra needed components (regulator, limiting resistor, decoupling caps..etc)

Thanks guys!

xl97:
I don't think use a buck is in option in this case.. as I'm designing the PCB and it all 'has to be on-board' (so to speak)..

That is simply a nonsensical suggestion.

If a "buck" regulator is what you need for the purpose, then that is exactly what you need to place on your PCB. larryd has illustrated a number of those readily available in modular form, designed specifically to be mounted as "daughterboards" on your own PCB.

It is not worth your time to attempt to replicate the sophisticated design of switchmode regulator PCBs, or indeed, to source the individual parts. And it would be foolish to use a poorer form of regulator which will take up more PCB space to allow for the heatsinking and reduce reliability due to increased operating temperature of the whole design.

These are simply functional modules. An ATmega328 is a functional module. You build something by putting functional modules together. It is mostly a waste of time and effort replicating the various parts of an Arduino when a Pro Mini can be used, mounted as a functional module.

I saw nothing that can be used as 'daughter board' above..

unless you meant through holes and the board stick straight up? (not really something I'm interested in doing then)

no links I saw had the 'half holes' (cant recall the official name) that can be soldered as SMD on -top- of the existing PCB design...

The specs (output) seem good though for what I'm looking for (enough current I believe)..

Castellated :slight_smile:

“ unless you meant through holes and the board stick straight up?”

There are right angled headers :wink:

And SMD headers:

BTW, you can mount things horizontally. :wink:

“Castellated”… yes! (DOH!)

thanks! @larryd

So,… let me ask some more ‘questions’ if I may. :slight_smile:

Talking about the last option you posted…

it looks as if there are only ‘3’ components to it? Thats it?

Could I just incorporate those 3 components into my board?.. replacing the SMD +5v regulator I am currently using?

If supplied with more than +3v (according to the listing specs)…

“Input Voltage:>3V;output voltage 5V;current 380-480mA”

This should be enough current for my needs…

this could then power the current +3.3v regulator… and I wouldnt need to worry about a ‘2nd’ +5v regulator to power the MAX chip (or neopixels if I go that route, which is looking doubtful)

Or am I missing/overlooking something? Or not heeding to advice from above in some form?

I believe the chip is a LM3671 (may be wrong thou), Google data sheet.

Read: 8.2.1.2

You should be able to do your own.

Why not buy them made up for 1$

larryd:
You should be able to do your own.

If you insist - as always - on "doing it the hard way".

larryd:
Why not buy them made up for 1$

With the nonsense removed: 5PCS Mini 2-in-1 Buck Boost Converter DC-DC 1.8-5V to 3.3V Step Up/Down Module | eBay

60 cents apiece.

"Point-of-load" regulation is absolutely the standard way to do things, complex boards can have dozens of regulators scattered about, no exageration. Then each part of the system gets the voltage, current and accuracy / low noise supply it wants without interfering with any other part of the system.

At low voltage you both lose voltage and board area if you distribute supplies post-regulation all over the board.

The pre-regulator supply traces can be much thinner as you don't care about the few 10's/100's of mV of drop across them, and you don't mind them picking up noise from other parts of the board either as the regulators will deal with that.

Its very common to see ADCs and DACs with two supplies, one clean for analog (high performance linear regulator), one dirty for digital (often switch-mode shared with the microcontroller/whatever)

When deriving 3.3V from 5V its important to use a low drop-out (LDO) regulator - a common one is the AP1117-33.

Thanks guys...

@larryd thanks for the link.

My current space is at a premium unfortunately.. and if I could just add in these 4 SMD components and replace my current +5v regulator.. it would be a good match/solution for me.

I understand the argument about 're-inventing' the wheel.. especially for more intricate/detailed boards..

I have added on Nano/Pro-MIni, DFPlayers, and other boards as-is (aka: as daughter boards).. so I'm not opposed to it in general.

Just in this situation, where space is limited.. and its ONLY 4 components.... I'm not really see a valid argument to NOT just add in the components?

Looking at the datasheet..

is that:

The LM3671 chip
4.7uF cap (IN)
10uF cap (out)
and.....?

  • what is that L1:2.2uH part?

  • any concerns with going this route and playing audio?

My current board: (my all-in-one compared to an Uno and its Waveshield)

that just has 2 LDO regulators (+5/+3.3v) works fine... audio is fine..etc..

I'm tryign to extend this design to add in MAX7219 (or Neopixels)... so I wanted to address having enough power.. but not clear if this will have any negative effect on audio? (I read things about noise..and power supplies, regarding audio...so I figured I'd bring it up?)

I'll order some of these LM3671 chips soon to play with. (maybe they also have a breadboard friendly one as well)

thanks

“what is that L1:2.2uH part?“

Inductor.

https://www.ebay.ca/sch/i.html?_odkw=w.w+uh+inductor&_osacat=0&_from=R40&_trksid=or m570.l1313&_nkw=2.2+uh+inductor&_sacat=0

One example, not sure about the current rating though:

larryd:
One example, not sure about the current rating though:
VISHAY 1206 Size 2.2uH Chip Inductor, ILSB-1206ER2R2K. Qty.100 | eBay

Link corrected.

Data Sheet:
[link removed by eBay]

They don't want you to know! :astonished:

50 mA apparently.
[/quote]

  • website is down.. LOL

Perhaps 2 possible candidates?

https://www.mouser.com/Passive-Components/Inductors-Chokes-Coils/Fixed-Inductors/_/N-wpcz?P=1z0wrhfZ1yzvlku&Keyword=Inductor+2.2uH&FS=True

1.) 2.2uH 20% 1MHz 900mA
Mfr. Part #
LQM31PN2R2M00L
Mouser Part #
81-LQM31PN2R2M00
https://www.mouser.com/datasheet/2/281/JELF243B-0013-1634236.pdf

2.) 2.2uH 110mOhms +/-20%Tol 1.2A HiCur
Mfr. Part #
CKP32162R2M-T
Mouser Part #
963-CKP32162R2M-T
https://www.mouser.com/datasheet/2/396/mlci03_e-1523425.pdf

I believe both are available in 1206 footprint.. which I can work with (most other components are 0603)

Thoughts?

Update:

Actually.. I just realized I have been looking at the wrong schematic this whole time?
Been looking at and talking about the +3.3v version?.. (right).. but in my head I have been thinking the +5v version.. because that is what I would need. that page has some many images! LOL

https://www.ebay.ca/itm/DC-DC-1-8V-5V-to-3-3V-Step-Down-Step-Up-Converter-Wifi-Bluetooth-ESP8266-CC1101/202548332357?var=502605564632

There looks to be 2 x +5v versions listed then?

One with a 'coil' type part (still inductor?) and the other +5v one has an IC and only 2 passives...

The LM3671 chip looks to be only for up to +3.3v

And the +5v version IC's in that ebay listing dont look anything like my failed attempt to find a +5v version at mouser!

https://www.mouser.com/ProductDetail/Texas-Instruments/TPS55065QPWPRQ1?qs=%2Fha2pyFadujGljhpsVn6vlivTlNcVzSPsZHBwoi990SDAjCo7z0BdNoDVQbLwNh3mfelLaWmXws%3D

LOL..

@xl97

Your links are screwed up. :frowning:

BTW
Make your own Castellated board by sanding off a Buck Converter's edge i.e. if it has a flat back.
Add Kapton tape on "Backside" :o

Another option: TPS5430

ODD?.. lol… I used the thread tools to post the links…

They are accurate, just need to copy and paste I guess?

Anyways… form the ebay link/auction…

I see these two as the +5v versions?

Questions for you pros: :slight_smile:

  • Why are there ‘2’ versions of a +5v board?
    ** (see attachment)

Looks like one board has:

‘coil’ (inductor?)
and a part that has:
“SS14” on it?

The other board:
2 x passive components
&
an IC that has:
218A

1549/50

on it?

I’d rather just get these tiny and few parts… and follow suit? Anyone help on the parts they used? (or why one board/approach would be than the other?)

@larryd
I like the sander trick! I could use my mill too… but the sander would be so much faster!
I’m gonna remember this the next time I’m going to ‘daughter-board’ one my pro-minis laying around (much better than using through hole headers all the time)

5v_versions.jpg

The visible coil version would be able to support more current.

16F0284C-7883-4923-B838-6C6062B20618.png


Sanding the edges off works well.

16F0284C-7883-4923-B838-6C6062B20618.png

Wow..

I didnt realize there were any components on the bottom!

Thanks for showing me.

500mA or so would be fine...

I'd actually prefer the other way.. but I'll give either way I try I guess? (first time/attempt for both)