External 5V Regulator

Hey all,
I was wondering what kind of circuit to make to hook a 5v switching regulator up with the Arduino (Arduino Mega). I don't want to desolder or remove the 7805 regulator on there already, but I want to power the circuit with my regulator, and not kill the Arduino. Any suggestions? Unless something bad will happen, I'll probably just wire up the regulator in parallel. Thanks in advance

So, would anything bad happen if I had a battery/wall-wart attached to the 2.1mm barrel jack, and used an external regulator connected to +5v, GND, and sourced from Vin? Thanks for the quick reply.

and used an external regulator connected to +5v, GND, and sourced from Vin?

You would be in effect putting two regulators in parallel. This is something you should not do especially if one of the regulators is a switching regulator. This is because regulators monitor the output in order to know how hard to turn on. If you supply this voltage by another means then the regulator will not turn on very much. This is a problem especially with switching regulators as they would become unstable and perhaps burn out. I am not saying they will but I am saying don't to it.

I was trying to see if I could use another regulator in parallel to increase the possible current output of the 5v pin. I suppose it'd be best to just cut the regulator off the Arduino to avoid parallel regulators, and just use the switching one? Thanks.

I was trying to see if I could use another regulator in parallel to increase the possible current output of the 5v pin. I suppose it'd be best to just cut the regulator off the Arduino to avoid parallel regulators, and just use the switching one? Thanks.

There should be no reason to have to cut out the internal 5vdc regulator. Just wire the external power source/regulator to directly power your external components that require +5vdc, just have to make sure the external regulator and Arduino have a common ground wire between them.

So you’re saying that I should have a separate 5v supply for the external components? Would I2C still work properly, as it requires usually a common 5v and GND in addition to SCLK and SDA? If so, this seems like a solution.

Is this an issue with power through the USB port as well?

I ask because I have a 5V switching supply powering both the Arduino (through the +5 pin) and some external components. I don’t use the Arduino Vin, but of course sometimes the USB port is plugged in.

Does this that on my 5V line I am effectively paralleling my switcher and power derived from the USB port? Is this a problem?

Part of the reason I do this is to minimize the number of wall-warts I need. If it is bad to have both USB power and power from the switcher on the 5V line, is it ok to feed both the switcher and the Arduino Vin from the same 12V wall-wart?

OK, "Arduino" = Arduino Mega in this case.

then they have on-board automatic switching so that the USB power overrides the power input barrel jack.

it's actually the other way around. :wink:

Lefty

Richard,

(a) I was not asking about overriding the power input to the barrel jack; my post asked explicitly about power supplied on the 5V line when USB is connected.

(b) The product page simply states "The power source is selected automatically." This is not especially informative about whether USB power (or power from the on-board regulator) is shut off when 5V is supplied on the 5V pin.

Alright, thanks everyone for your help =).

(b) The product page simply states "The power source is selected automatically." This is not especially informative about whether USB power (or power from the on-board regulator) is shut off when 5V is supplied on the 5V pin.

There is no provision on the standard Arduino boards to shutoff on-board voltage source(s) if one applies an external regulated +5vdc to the +5vdc connector pin. It is not good engineering practice to have two voltage sources wired together for several reasons, however many have done so and have not reported problems with it.

I have a 5V switching supply powering both the Arduino (through the +5 pin) and some external components.

If the "engineers of the future" can't figure out which way the electrons are flowing from that, God help us all.

Aeturnalus, heres what you can do.......

Build a switching circuit that outputs 5v supply. Since a switching circuit uses pwm method for generating an output, use a 12v,1.2 AMP-HOUR dc
battery to power it up.

At the output terminal of this circuit, connect a female USB connector. Connect this USB socket to the USB input socket of the BOARD.

Since the USB input plug of the BOARD is provided so that it may draw a 5v output from the computer supply if no other power supply is given to the BOARD, the 7805 wouldnt be connected to it and so, no problem of connecting regulators in parallel :wink:

Since the USB input plug of the BOARD is provided so that it may draw a 5v output from the computer supply if no other power supply is given to the BOARD, the 7805 wouldnt be connected to it and so, no problem of connecting regulators in parallel

That is how I do it when wanting to use an external +5vdc regulated power supply. That also allows the board to still utilize the built-in thermofuse protection.

Lefty

lefty, whats the IC that you use for the external switching circiut?

lefty, whats the IC that you use for the external switching circiut?

I've never had to build a switching power supply. Just so much more cost effective for me to find small switching regulated +5vdc 1 amp cell phone chargers at thrift stores. Usually for 1-2 dollars.

Lefty

The USB plug trick sounds nice, is the fuse on the Arduino/Mega set to open on temperature or on current? If I remember correctly, it's a 500mA polyfuse... and I'm running ~3A through the regulator (servos and suchlike). In regards to the cheap +5v DC switching regulators for cell phones, while I do use those on occasion, this application is for a robot... and thus must be powered off a battery.

and I'm running ~3A through the regulator (servos and suchlike).

There is no way that you can route 3 amps of voltage through any connector on a Arduino board and then on to external circuitry like servos and such. When using the USB as the power source you are limited to 500ma by the polyfuse, when using the external power connector (with a 7.5-12volt supply, not +5vdc) you are limited by the 1 amp polarity protection diode rating. One might wire a regulated +5vdc power source directly to the Arduino +5vdc connector, what would be the point as that is the only connector pin avalible would then be utilized as input power and not avalible anywhere else to route to external loads like servos, etc?

So I guess I need further info on what specific problem you are trying to solve?

Lefty

I'm trying to solve the problem where I do not have enough current to easily run the servos and sensors I need. As it is now, I've got the 5v regulator on the Arduino powering the Arduino itself, and the switching 5v regulator attached to the Vin and GND pins, with its +5v output going to power rails on my circuit. If I could use the +5v to power both the Arduino and the external circuitry, while still having power going through Vin from the battery (motor shield), it would be best. I was hoping the USB idea would be able to do that.