I looked at that particular drawing and unless I am missing something I would not use it as drawn. They use a 14 volt wall wort to bring in about 14 VDC. The diode scheme is fine and theory of operation is fine but they incorporate a 5 Volt regulator like the LM 7805. While as drawn the circuit will output a constant 5.0 Volts the problem becomes with the Arduino board external power jack. The board is designed for external DC power with a range of 7 to 12 VDC, not an external 5 VDC. According to the Arduino documentation, the Uno uses a 5-volt linear voltage regulator in a TO223 SMD package. The regulator is easy to see right beside the external power connector. The on board regulator is supposed to be a LDO (Low Drop Out) type but the minimum external voltage should be 7 VDC allowing for the regulator drop out overhead. All of this can be bypassed by connecting 5 VDC to the 5.0 Volt Pin but this is not recommended. "The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it".

I have noticed running my Arduino Uno board on an external 12 VDC through the external power connector the LD50 regulator does get a little warm to the touch. Not at all hot, just a little warm. Anyway, I would not apply 5 VDC regulated to the external power connector as the on board regulator likely won't work. I did try it with 5 Volts on my board and the board appears to work but I can't say if all boards will work and work correctly? Beats me.

Ron

There's nothing special about the Arduino in board regulator. If your external 5V supply is solid and clean there's no reason not to inject 5V at the 5V pin.

If there's a lot of wire in between and you're worried about noise pickup on the 5V leads, then you might want local chokes and/or caps at the Arduino pin. However, if the power is clean and the leads are short, what's the difference?

All that said, in the Instructable linked previously, they're stepping 12-14V down to 5, requiring a bypass of the Arduino regulator, and either dropping a lot of power through their 5V regulator or using a SMPS, which is likely noisier. Perhaps a better all around approach would be to do their plan, but step down to 7-9V (whatever is convenient) externally, then feed the Arduino regulator with that. That way, you spread out the power dissipation, and potentially gain a little efficiency from using an SMPS externally, while still getting the clean power from the Arduino's linear regulator.

 

There's nothing special about the Arduino in board regulator. If your external 5V supply is solid and clean there's no reason not to inject 5V at the 5V pin.

If there's a lot of wire in between and you're worried about noise pickup on the 5V leads, then you might want local chokes and/or caps at the Arduino pin. However, if the power is clean and the leads are short, what's the difference?

All that said, in the Instructable linked previously, they're stepping 12-14V down to 5, requiring a bypass of the Arduino regulator, and either dropping a lot of power through their 5V regulator or using a SMPS, which is likely noisier. Perhaps a better all around approach would be to do their plan, but step down to 7-9V (whatever is convenient) externally, then feed the Arduino regulator with that. That way, you spread out the power dissipation, and potentially gain a little efficiency from using an SMPS externally, while still getting the clean power from the Arduino's linear regulator.

I agree absolutely. Where I mentioned: "All of this can be bypassed by connecting 5 VDC to the 5.0 Volt Pin but this is not recommended. "The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it". I was merely quoting what the nice people at Arduino mentioned least I have someone point out to me Arduino says no. Would I do it? Heck yeah, I would and it works.

Ron

 

View attachment 144650 Here is a photo of the IBM impulse master clock emulator showing the MP1584EN DC to DC converter I am using. Here I use 24 volts to power the clock movements and drop from 24 volts to either 7.2 volts to the VIN pin or 5 volts to the 5 volt pin of the Arduino. The nice thing about this device is that it is short circuit protected and runs cold, since it is a switching power supply. Noise has not been a problem with this configuration even though this application is switching inductive loads containing CEMF spikes. Joe

 

A word about the Raspberry pi zero W (wireless LAN) configuration shown in the previous posting of the RPi schematic with back-up power provisions. The backup power battery pack [including its DC to DC converter] will be connected to the mini-USB +5 volt power connector on the RPi zero W board. When commercial power is lost, I also loose the power to all seven of my clock secondary movements. I do not want to power the secondaries from batteries so software senses the power loss at the RPi GPIO pin 5 and notes the time, but keeps running under power from the battery. When commercial power returns, the software notices and advances the movements up to 12 hours. If power is out longer, the RPi just figures out the nearest hour in a 12 hour period and brings all secondaries back to the correct time. IBM has a mechanical attachment that can mount to the master clock's movement called an accumulator, but can only correct for 12 hours of lost time. Then it has to manually be corrected. My RPi is all automatic for as long as it's battery last. The Yellow LED is the power good LED and will illuminate with either 12volts (dimmer) or 24 volts connected. This battery backup feature works great! Photos are of two RPi Zero Ws running and a close-up of one of the driver hats. One is using 24 volts and the other is using 12 volts for a 12 volt secondary coil. I am still working on making a battery pack. Joe