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Topic: Project assistance: voltage regulator and SMD caps for it (Read 162 times) previous topic - next topic

xl97

I am working on a project/making a PCB that has:

1.) all components on one side, DFPlayer, Arduino Pro-Mini, regulator, resistors/caps..etc..

* the main modules will be connected using SMD male headers  (not through hole)

2.) the other side is all 5050 WS2812 (Neopixel) leds....   current count and arrangement is still be worked out..  but in the range of: 36+ leds.....  I would imagine roughly 1A or so being pulled by these (not full white and maybe a little blue, or just full white..  so maybe 25mA per led I'm roughly calculating at)


I have used these linear regulators in the past:  (same pinout as the common LM7805 regulators... but this one is rated for up to 2A)


BA50DD0T

TO220FP-5

https://www.mouser.com/ProductDetail/ROHM-Semiconductor/BA50DD0T?qs=%2Fha2pyFaduiMHlRy%252BIND8WHFNqRf2tHq029GH4vcoEk%3D

This datasheet is hard for me to read as the diagrams (to me..  I'm sure those more experience it might be easier)..

Anyways..  around page 14.. it says to use a:
*Please attach a capacitor (greater than 0.33μF) between the Vcc and GND

Then in diagram:  Fig.32  Output  Equivalent  Circuit
* it shows using a 22uF cap on the output.

Do these need to polarized?  (a tant or electrolytic type capacitor?)

In previous builds.. I used through hole electrolytic ones..  (been a while Id have to go back to be 100% sure)..

but now I want everything to be SMD  (so ti can all remain on 1 side)..

Do they make 1206 sized caps that will work?   Can I use 1206 ceramic caps in this?



Alternately..   if anyone has a schematic for for a DC-DC booster circuit  (I have found some modules on ebay, but I'd rather have an Eagle schematic this time, to add it into the design itself, instead of an external module)..  so I can just use a +3.7v li-ion pack.. instead of a +7.4v li-ion pack...

** I also have not found one that is fixed +5v output... and have over 1A of current.. (most say 400-500mA with +5 or more input)..


You guys are always good at showing me the way... and even sometimes...'shaming' me to the correct way!  LOL

I'm also open to other solutions.. but not something that makes this project more difficult....  or is another 'project' in itself...

But if there is a different/better regulator to use..... or correct (polarized?) caps to be used....   or even swapping out to Boost circuit to use +3.7v li-ion packs..

Thanks!














Paul_KD7HB

Since you are using the SMD version of the device, you have to take care of the heat dissipation through the chip's belly pad. That probably means a pattern of vias to a ground plane on the other side of the board.

Paul

xl97

HI @Paul_KD7HB

I'm actually using the through hole component (like the only one in this project) of the v-regulator...   but was trying to source/find correct SMD caps for it.

TO220FP-5 is the #


I cant tell if these need to be polarized caps?  or just ceramic ones?  If just ceramic.. then I can use any old 1206 cap?

But if polarized....??   Not sure what my options are?  Do they make polarized caps in that size?  Do I need to use a different part/footprint?

But I am open to other viable solutions that can supply enough current, and I can find correct SMD caps... (which is what I'm leery about)

Or.. if anyone has a DC Boost circuit/schematic that can share?  (usually some IC and handful of passives?)  

PerryBebbington

#3
Feb 14, 2020, 11:24 pm Last Edit: Feb 14, 2020, 11:28 pm by PerryBebbington
I can't tell if these need to be polarized caps? 
No capacitor in any circuit needs to be polarised. Capacitors are not polarised in order to fulfil some circuit requirement, they are polarised because the techniques involved in manufacturing a high value (> roughly 1μF) capacitor result in a capacitor that is polarised. In an ideal world there would be no polarised capacitors, but no one, to my knowledge, has invented a technology that produces a high value, compact non-polarised, capacitor.

The question you are asking is the wrong one, the question to ask is 'do they need to be non-polarised?'. For what you are doing polarised will be OK.

xl97

ok.. usually when I see a schematic  (not a pro.. just a hobby guy).. the cap 'symbol' usually shows a specific one that means polarized or not.   I see nothing that shows me either way on that diagram in the datasheet.

I'm not 'wanting' to do polarized....  just trying to follow the schematics usually.  I thought sometimes you needed polarized caps that NEEDED to be (required) connected to the correct GND/VCC 'rails'...

I had two -through hole- caps in the schematic (from a previous project).. I changed them to be 1206 footprints..

I then started to question:

* Do they need to be polarized?   (I guess your saying no then....correct?.... and thank you for the explanation line)
* If they needed to be.. is that even a realistic part?  (1206 electrolytic caps?)

So to re-cap:
I can use any cap I want for that v-regulator?   as long as they fit the datasheet?

*Please attach a capacitor (greater than 0.33μF) between the Vcc and GND
* it shows using a 22uF cap on the output.



so,......any ceramic 1206 cap will work?

Wawa

I have used these linear regulators in the past...

...but this one is rated for up to 2A
We all did, last century.

Dissipation (heat) will be the limiting factor, not the 2A rating.
2C LiPo to 5volt@1Amp could be ~3watt. That requires a heatsink.

This one does it without, and the caps are build-in, and you can use it upright like an LM7805.

Bigger version.
Leo..

xl97

I understand what you are saying.. unfortunately for this project using an external module just wont work.. unless its whole footprint is same size as an LM7805 (which at that point I'd give it a shot I guess?)

update: looks like both would fit? @ .7"   (that would be terribly hard to mount using SMD male headers though unfortunately, because it only has one row of holes/vias)



So if there was a schematic with parts numbers or something.. I'd definitely attempt to incorporate it into the pcb itself.

That being said..

* If I would go the adding in another 'circuit' to step-down the voltage route.....   would it be better to use a 'step-up/boost' circuit?  So I can then use just one +3.7 li-ion/li-po battery source?

* I have not found a boot module/schematic that can provide more than 1A of current..


Wawa

I have used modules like that horizontally on pin headers. See image in post#10 here.

Buck is easier on the battery (half the current), and generally more efficient.
Use the voltage regulator select page on the Pololu site.
>=1A boost here.

Don't forget the heatsink on a linear regulator.
That could make it five times the size of these switching regulators.
Leo..






xl97

Looking at your pic in post #10 (other thread)..

I cant really see your headers?  Are they merged/part of the screw terminals as well?

Are they sitting FLUSH on the PCB?  (ie: flat?)

I have to use SMD male headers here.. so the modules would be slightly lifted due to the black plastic stuff that holds/aligns the pins.

update:  I was looking at the wrong module in your pic.  I was stuck looking at all those other boards (multiples).. and glazed right over the module in the middle..

So it just 'free floats' a bit on the other side? (opposite side of where the headers are?)


Looking at the second link.

I dont see where it says >1A output?

Specs tabs doesnt even have a MAX CURRENT OUTPUT entry..

and on the other tabs I see this:  "typical efficiency of 80-90% when doubling voltage and with 100-500 mA output"

Wawa

Yes, the module is connected to the board with a common straight 4-pin header (came with it).
Distance is the plastic spacers of the pin-headers. The other side of the board is just 'floating'.

Look at the first graph (left) on that boost converter link.
3.3volt in, 5volt out, just over 1Amp.
Could draw ~1.8Amp from the LiPo battery to deliver that 1Amp.
Leo..

PerryBebbington

#10
Feb 15, 2020, 11:16 am Last Edit: Feb 15, 2020, 11:17 am by PerryBebbington
ok.. usually when I see a schematic  (not a pro.. just a hobby guy).. the cap 'symbol' usually shows a specific one that means polarized or not.   I see nothing that shows me either way on that diagram in the datasheet.

I'm not 'wanting' to do polarized....  just trying to follow the schematics usually.  I thought sometimes you needed polarized caps that NEEDED to be (required) connected to the correct GND/VCC 'rails'...

I had two -through hole- caps in the schematic (from a previous project).. I changed them to be 1206 footprints..

I then started to question:

* Do they need to be polarized?   (I guess your saying no then....correct?.... and thank you for the explanation line)
* If they needed to be.. is that even a realistic part?  (1206 electrolytic caps?)
You're getting it backwards. If you design a circuit with, for example, a 1000μF capacitor then that capacitor is going to be polarised. You can't buy a 1000μF non-polarised capacitor. You could make one from lots of low value non-polarised capacitors but it would be enormous and cost a fortune. You'd have to have a very particular reason for doing so. So, your design requires 1000μF, which of necessity is going to be polarised so you show that on the schematic so it's clear which way round it has to be installed. It is NOT shown as polarised as a way of saying 'this must be a polarised capacitor', it is shown as polarised as a way of saying 'as this will be a polarised capacitor this is the correct way round to connect it'.

In general, across a power supply capacitors larger than specified are fine.

xl97

@Wawa

What are your thoughts on this step-up/step-down module:

https://www.pololu.com/product/2836/specs

I suppose it allows for a wider ranger of battery sources?

+3.7v li-ion/li-po  up to +7.4v li-ion packs...etc..etc  (16v really..  but those were more so my -options- if you will)

And one can choose what they would like to use and get better/worse run-times

Wawa

Never used that one.
Buck/boost used to be less efficient, but that one doesn't seem to suffer from that problem (see graph).
Leo..

xl97

Guess its worth a shot?  lol  :)

I didnt seem to find anything similar on ebay (clones) that were cheap..

Well none that seemed to output over 600mA  :(

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