I want to make my self an custom PCB (with EasyEda) that i will power widt an old computer power adapter. I want 5-10 outtakes with 5v and 3.3v for powering several projects as Arduino and ESP32 etc.
I'm going to use buck converters for downgrading the voltage.
My question is, do i need capacitor in this circuit?
If yes, why and what value?
I Think i'm going to use an old laptop adapter that gives 19V for main power to the board.
I would not add any capacitors .
Ok, thanks 
Depends on the regulator you use.
I would use switching regulators such as these
https://www.digikey.com/en/products/detail/murata-power-solutions-inc/OKI-78SR-3-3-1-5-W36-C/2259780
https://www.digikey.com/en/products/detail/murata-power-solutions-inc/OKI-78SR-5-1-5-W36-C/2259781
See page 19 of datasheet. Certainly wouldn't hurt to leave pads for caps.
Similar devices from Pololu.
Which you select depends on the current load you need to support.
For a moment I thought you were talking about an ATX supply - which has lots of power in 5V and 3.3V available.
For stepping down 19V to 5V (to 3.3V even more so) a buck converter is definitely the way to go. With a linear regulator you're burning off almost 75% of the input power in the form of heat, all concentrated in the regulator. Not going to work for long.
Ok thanks.
Maybe i want to implement a reverse voltage protection on the board. Four diodes will do the trick i think. ?
When designing a custom board such at this you should add as many added components as you can think of. That is unless you have a space constraint. You should also design in holes for mounting, even if you don't plan on mounting at this time.
By extra parts I mean:
Remember you can always leave parts off if you don't need them, but its a pain to add something after you receive the board.
Also remember this is a power supply, shorts and other miswiring will occur, make the copper traces as thick as you can get them. DO NOT rely on the "minimum" with of the traces specified by the board mfg. Also remember vias are not good for power. If you must use them make the hole larger than the minimum and use multiple vias in parallel.
Why polarity protection on the power supply? Overcurrent protection makes a lot more sense to me. The power supply should be designed in a way that it always produces a known polarity. Just by using buck converters you can pretty much ensure this.
You may add reverse polarity protection on the input side of the power supply board - to make sure that the 19V input is connected properly. A p-channel MOSFET makes a lot more sense than diodes (do a quick Google search for schematics), assuming you want more than about 100 mA of current.
Likewise, the projects that are powered by this power supply may benefit from reverse polarity protection. For low currents a diode (mind the 0.5-0.7V drop, that's too much for many a 3.3V project), otherwise a p-MOSFET.
Some will add capacitors and other not. What is the right thing to do?
Goood advices there, thanks
Depends on your intended load, and how much capacitance the buck converters have already.
In general, bulk capacitance is best kept close to the load it has to decouple, so not at the power supply.
wvmarle:
Depends on your intended load, and how much capacitance the buck converters have already.In general, bulk capacitance is best kept close to the load it has to decouple, so not at the power supply.
I'm going to give power to microcontrollers. Arduino, ESP8266 etc. Max teoretical current from lets say 6 ports is around 2.5 amp. Maks 4-500mA pr. port.
Most likely much less than that.
You don't plan on connecting anything to those microcontrollers?
Some sensors and other usual thing we use microcontrollers for i guess.
If that "other usual thing" includes things like small steppers and servos, make sure you scale your power supply accordingly you you're going to need separate power supplies for that.
Good point there
Maybe use an more powerful buck converter that can deliver more amps. But that mean i have to use a bigger one...
Setting really old ATX Form Factor designed power supply units the newer units, last decade or so, can be had relatively inexpensive depending on how much power you really need. They offer 12.0 VDC, 5.0 VDC and 3.3 VDC all of which are popular voltages for the home hobby enthusiast. Suffice to say in a $25 to $200 USD price range someone should find something that trips their trigger.
Here is something I don't quite get.
"I want 5-10 outtakes with 5v and 3.3v for powering several projects as Arduino and ESP32 etc".
Those are common outputs with current to match whatever model you choose. You will have regulated clean DC voltages of 3.3, 5.0 and 12.0 within a Normal 5% tolerance. Most will also accept an input voltage of 90 to 250 VAC 50/60 Hz. So I don't get the references to use of a buck or boost converter?
There are likely a few hundred design suggestions out there Online and assorted breakout boards to simplify your design. Again, pretty much up to you. Any breakout can be easily expanded. Things like pilot lamps are also easy additions. More features? Add a DC Voltmeter and Ammeter for each voltage since they can be had inexpensive. The 5 volt SB (Stand By) offers up a few more options.
You start with a clean sheet of white paper and a pencil with a large eraser. List the features you want/need and then a rough sketch of where things get placed.
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____The old Intel Desktop Platform Form Factors Design Guide covers what a well made power supply will or should do.
Ron
Where does the ATX comes from?
Read the very last line of my first post.
I,m going to use an 19V laptop power adapter as main power to the board. Therefore i need buck converteres. I do not want my microcontrollers let out the smoke yet
I Think i'm going to use an old laptop adapter that gives 19V for main power to the board.
OK, my bad in not picking up on that. Depending on the current loads years ago it would have been shunt regulators mostly giving you high heat to remove and lower currents. Today we have all sorts of Buck Converters improving quality seems like every day along with efficiency.
Somewhere on the 19 VDC supply you should dee a rating. I have an old 19.5 volt 6.5 Amp 130 Watt rating, so you know what you have to work with. Obviously, even on a good day you can't get out more than you put in.
I would just consider using a few of these buck converters. A nice feature is the wide input range and adjustable output range. Each module is rated for 3 amps. Simple with no extra excessive components needed, close to plug and play.
Ron
Ron_Blain:
OK, my bad in not picking up on that. Depending on the current loads years ago it would have been shunt regulators mostly giving you high heat to remove and lower currents. Today we have all sorts of Buck Converters improving quality seems like every day along with efficiency.
Somewhere on the 19 VDC supply you should dee a rating. I have an old 19.5 volt 6.5 Amp 130 Watt rating, so you know what you have to work with. Obviously, even on a good day you can't get out more than you put in.
I would just consider using a few of these buck converters. A nice feature is the wide input range and adjustable output range. Each module is rated for 3 amps. Simple with no extra excessive components needed, close to plug and play.
Ron
When that said... Yesterday i got some awsome silicone cables from AliExpress. I have never own cables like that before. This is really an eye opener for me. Soft and bendable cables with high quality. Not cheap, but mutch cheaper than if i bought it here in Norway.
I thinking something like this:
