I'm making a quick-and-dirty project where I have three 12V LED spotlights (7W each) and I want them controlled by an older (5V) Arduino Nano. I already have all of the parts, so I'm trying to do this without buying anything new (or as little as possible).
Now, I understand that I can just power the Nano off of the same 12V supply that's powering the lights, but I have a couple LM78L05 linear regulators lying around, so I wanted to know if I could use one of these to take some of the heat off of the Nano.
Could someone suggest a suitable circuit for this?
If it helps, I have a few other "power supply" type components here too: MBR735G schottky diodes, 1N5819 schottky diodes, and a few 6N137 opto isolators. Plus various resistors and capacitors.
A bit of a random question, I know, but hopefully someone has a circuit in mind that they've used in the past.
That regulator is only good for 100ma, so I wouldn't put my money on using it for a Nano. You might get away with it, with nothing else drawing any current, but it's an iffy bet. 7805, sure! Better yet, drop in a 7808, then run it's output into the Vin pin of the Nano.
Ah, I didn't spot that the output is only good for 100mA. Still, there won't be anything else attached to the nano (just flipping the MOSFETs with 5V) so maybe it would be enough? Again, I'm trying to use existing parts here.
Would it be better to just power the nano off of the 12V rail? Or should I really get a 7808?
powering from 8V instead of 12V means the Arduino regulator must dissipate 4Vx(whatever current) less power. Very good for the regulator.
I can't tell you much about how to proceed, it'll depend on how you're controlling the spotlights.
@mancera1979 Yup. It does. And look at the power dissipation curve - if you feed it 12VDC, how much current can you regulate, presuming you don't overheat it?
Seems pointless. The Nano's (assuming you mean classic Nano 3) onboard regulator will be fine to supply only itself and a drive a few MOSFETs. Using an external regulator won't have any significant benefits, it's just a waste of components.
That said, some questions:
This 12V supply. Is it a vehicle? That is a hostile environment for electronics. The supply can reach 15V or more when the alternator is running, and there can be nasty high voltage spikes caused by the ignition system.
Do you plan to switch the spots on and off or dim them using PWM? Dimming using PWM can draw more current, and the higher the PWM frequency, the higher the current. At typical Arduino PWM frequency (<~1KHz) it won't be a problem I think, but at higher PWM frequencies, it might become significant.
Use a 7805 to power external devices (instead of relying on the Nanos 5v pin)
Power the Nano from the 12v via three 1N4004 rectifier diodes in series - this will put just under 10v into the Nano, significantly reducing the heat and providing some extra protection.
