Welcome aboard, Karin! I am a retired EE too.Īdding to what FlightRisk said, linear (including LDO "Low Drop Out") regulators draw the same input current as they output. You wouldn't normally melt one to do short-term tests if you want to play, but they do seem to fail when they are run hot. But let's say it can dissipate 2W, then I = P/E = 2/10 = 200mA before thermal shutdown. I hate to use the "I think I remember" phrase, but apologies in advance, I think the SOT version of the chip can only handle 1.5W with no heat sink with the copper on that board. That's hot It goes into shutdown at 175C. At around 80 degrees C per watt trying to follow the ambient temp / junction temp graph, 80*2 = 160C. So even at a meager 200mA, that is (15-5)*.2 = 2Watts. There are a lot of variables as you know, what else is being driven off the board, ambient temperature, heat sink and if it is it sinking or sourcing current to pins, etc. You can check the thermal characteristics on the datasheet and the board layout to see there is very little heat sinking on the board for that regulator. If you put a motor shield and a wifi board on it, you will normally have enough current at 15V to overheat the chip. You can do the math at 500mA you have to dissipate 5 Watts of power. Even with the thermal shutdown circuit which puts the regulator into this oscillating mode, You are wasting 10V that turns into heat. The only other draw back to providing CPU board power via the Motor Shield would be possible current spikes being impressed on the CPU input power. Please get a little technical about the response, as I am degree retired Electrical Engineer and have tons of experience designing and building embedded computer and communication systems. The only load that the +12 volt buss from the two pin power connector sees is the NCP1117 regulator which then feeds the rest of the +5 volt loads on the CPU board. The current being drawn by just CPU board by itself yet, so I am guessing that the caveat about exceedingġ2 volts DC is due to the heat sink capability of the CPU board. The spec sheet for the NCP1117 indicates max safe input voltage at +20 volts DC. Not exceed 12 volts DC being fed to the Mega board. Even though the Arduino docs say it is recommended to I have powered up just the Mega 2560 with downloaded codeĪnd it appears to send packets all ok, by monitoring the pins with an oscilloscope.Ī basic question for the assembled masses. I have an Arduino Mega 2560 rev.3 and the Arduino Motor Shield. I've been looking at the DCC++ system, and it intrigues me.
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