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How much current do you require in Arduino/Sanguino or other embedded systems projects?

After responding to the LM2575 inductor question I started to take a closer look at the TI power DC-DC converters. It would not be difficult to replace the linear regulator + or'ing diodes on all my Arduino/Sanguino compatible boards with a TI step-down converter.

This would provide a >90% efficient conversion, input voltages from 5-15V and a 2.5A output that is regulated and adjustable. What would be sacrificed would be the ability to power off of the USB. The incremental cost would be in the $5-$8 range. Wider range inputs are also possible.

Is the 500mA you can get from the USB port all you ever need? Would this be useful in your projects or is it too little current?

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About the worst case current draw I have seen from a higher-end micro controller is about ~200 to 300 mA. This was the LPC2388 (ARM7, 32-bits) with the usb, emc, and all the more power hungry peripherals turned on running at the highest clock speed (288MHz internal PLL divided down to 72MHz). Generally, I would highly recommend going to switching regulators if cost, noise, and complexity is not an issue.

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I've been using my own custom arduino compatible. I've actually gone with a 150mA voltage regulator because I generally don't need more than 75mA or so. I have done a couple projects that required more than that - one that needs ~250mA and another that actually needed a full amp. I've got another in the works that'll need considerably more to drive a motor, but I intend to bypass the regulator and only use the regulator for the ATtiny chip on that one.

So... 90% of the time I've needed 75mA or less. If I need more, I've been able to get away with swapping out for a heavier voltage regulator like a 7805 (I picked my smaller regulator to fit in the same footprint).

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You are really asking two separate questions: 1. How much current can you drive through the Arduino and 2. How much current do you expect your project to use?

Answering 1. is easier: Max current is 50mA / pin on the 328. The Arduino has a fuse at 500mA total: http://www.arduino.cc/en/Main/ArduinoBoardDuemilanove

There really is no simple answer to 2 - this discussion leads into the importance of signal level vs drive level currents. One goal should be to keep signal currents as low as you can get away with. (This is really a separate discussion).

You can easily switch an amp with a TO-220 package transistor, and if you need more you can use relays to drive whatever current you like. However, as a general rule of thumb I like to take extra safety precautions if I am going above about 12v / 1amp.

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  • \$\begingroup\$ The fuse tells the story. Mine tend to draw about 300-320 with some I2C going on. That is roughly 3/5 of the rated current that will blow the fuse. Never have seen one blow out. \$\endgroup\$ – SDsolar May 29 '18 at 20:00
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My worst case current draw is around 320mA - Arduino, Ethernet shield, XBee, SD Card, and a few I2C devices.

I would seriously consider a switching regulator - in fact I often power Arduino mini pro + peripherals from a 5v switching regulator and bypass the on board linear regulator.

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The only time I ever need more than 500 mA is if I'm driving a bunch of LEDs. Even running an FPGA, microcontroller, and RAM only draws ~200-300 mA.

Though, if this device ever needs to be certified by the USB IF (i.e. you want to go commercial with it), you should be aware that during enumeration, a USB device is only allowed to draw 100 mA. After enumerating successfully, it can request 500 mA from the host. The host can deny this request.

Now, most USB ports will feed you your 500 mA before enumerating, so you probably won't ever experience this limitation...unless you send your device to the USB IF for testing, in which case they will most certainly fail you.

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