Power ARDUINO (via Vin) and own PCB with switching power supply

Hi,...I just tried to power the ARDUINO (UNO) with a (cheap) switching power supply directly via Vin! Attached to the ARDUINO there is a breakout board with a TLC59116 (LED-driver; which is also powered directly from the power supply. There is no regulator on the board!) to which 16 LEDs are connected! I wrote a little program that switches all LEDs on and off periodically and everything works fine! I tried the direct connection of the power supply, because I am just layouting a PCB with an Atmega328P a L293d (motor-driver that will drive one tiny 200mA motor and a few LEDs) and two TLC59116 (with at all 32 LEDs connected that will be driven with 15mA each with 97kHz PWM) connected to it and i am thinking of powering this without any power regulator on the board! The max. current of the board will be about 1A! The switching power supply I used for the test has a capability of 2,2A! As the board I am layouting will not be very cheap (only SMD components on it) I would like to know how risky it is not to use power regulators on the PCB (I will not try the layout on a breadboard!)!? The reason that makes me think of getting rid of (linear) power regulators is that I would need TWO (e.g.) LM340 (SMD) regulators (with capacitors) and therefore "much" space. Also for space reasons I don't want to use heat sinks or power regulators that are not SMD! Thanks for the answers in advance!

You didn't mention once the voltage of your 2.2amp switching regulator, what is it?

Lefty

...it's 5V!

Joegi: ...it's 5V!

In that case:

Hi,...I just tried to power the ARDUINO (UNO) with a (cheap) switching power supply directly via Vin!

That won't work, as the Vin pin just goes to the input of the on-board linear +5vdc regulator which requires a voltage between +6-12vdc to the input of that regulator. You can however wire an external regulated +5vdc voltage source to the arduino +5v shield pin and that will power the Uno board property. Don't forget to wire the negative terminal of the external source to a arduino ground pin.

Lefty

...oh, you are right, but it worked with 5V (I measured the voltage of the power supply and it is 5.17V) going to Vin!!!

...now I connected the power supply to the "5V shield pin" and it worked fine (,too)! So whatever the reason was that it worked with "Vin", back to my question if it is a good idea to power the above mentioned hardware directly (without additional power regulators on the PCB) to a switching power supply or not!

Joegi: ...now I connected the power supply to the "5V shield pin" and it worked fine (,too)! So whatever the reason was that it worked with "Vin", back to my question if it is a good idea to power the above mentioned hardware directly (without additional power regulators on the PCB) to a switching power supply or not!

Many people do, it's really your call. The only issue I can see is if you then plug in the usb to load new sketches then you will have the USB's +5vdc from the PC wired directly to your external regulated +5vdc supply. That is not considered a good engineering practice, but many do it and have not reported any problems.

Good luck

retrolefty: he only issue I can see is if you then plug in the usb to load new sketches then you will have the USB's +5vdc from the PC wired directly to your external regulated +5vdc supply. That is not considered a good engineering practice, but many do it and have not reported any problems.

The Atmega328P on the PCB won't have a USB connection, but "Rx", "Tx", "Reset" and "GND" on a header! I already made a (my first own) PCB with (as main components) an Atmega328P and a L293d (motor-driver) and such a header on it and do the programming with an Arduino Duemilanove (without Atmega) that is connected to the PC. I reprogrammed that (PCB-)Atmega often and encountered no problems!

Joegi:

retrolefty: he only issue I can see is if you then plug in the usb to load new sketches then you will have the USB's +5vdc from the PC wired directly to your external regulated +5vdc supply. That is not considered a good engineering practice, but many do it and have not reported any problems.

The Atmega328P on the PCB won't have a USB connection, but "Rx", "Tx", "Reset" and "GND" on a header! I already made a (my first own) PCB with (as main components) an Atmega328P and a L293d (motor-driver) and such a header on it and do the programming with an Arduino Duemilanove (without Atmega) that is connected to the PC. I reprogrammed that (PCB-)Atmega often and encountered no problems!

Then I see no reason why you shouldn't use your external regulated +5vdc voltage to power you project, 328p and all.

Lefty

...would you recommend to use an E-CAP on the PCB (PCB without own regulators)?

Joegi: ...would you recommend to use an E-CAP on the PCB (PCB without own regulators)?

Always recommended to have at least one maybe 100ufd filter cap for the whole board and at least one .1ufd ceramic cap mounted close to the power pin and ground at every IC chip. The 328p chip could use two .1 caps, one at Avcc and Vcc pins and one at Aref pin.

Lefty

...thanks!

The output of a switching power supply is usually well regulated and buffered (capacitor) already. This means it’s generally a perfect replacement for the linear regulator on the board itself. Thus, you should be able to tie the power supply to +5V and to GND, and power anything that way. No additional components needed.

If I want more robust power in my circuit, then I would add, in order of preference:

  • a polyfuse/PTC resettable fuse in series (use a low resistance one!)
  • a TVS protection diode in parallel
  • a polarity protection diode in series (use one with low forward voltage drop!)
  • a 1uH inductor/choke in series
  • a 100uF capacitor in parallel
    Also see sketch of Super Robust ™ Input :slight_smile:

Assuming you get components that can take the current of your Arduino plus your additional components, you only need one of each.