The photon cannot be supplied 12v directly so I wanted to get a L7805CV 5V 1.5A voltage regulator and then connect that to Vin and Gnd to power the photon. Also I was planning on using neopixels so could I put them in parallel to get 3 amps?
Yes you could use that regulator to run the Photon.
I wouldn’t use those to run 3A of LEDs. It’s a linear regulator which basically means it burns the excess voltage as heat. 12V-5V=7V @ 3A = 21 Watts. That would take a big heat sink.
A better idea to use a DC/DC buck converter, it will be more expensive but much more efficient. Here’s one:
Oh I wasn’t aware that those voltage regulators are just voltage dividers so they waste the rest of the power as heat. Isn’t that super inefficient?
So you would recommend a buck converter instead?
Something like this? amazon link
Will you be using a 12v battery to power your project or a wall plug (AC)?
I was using a Traco TSR12450 which does not provide the amps you’re looking for but I bet you could search their product lineup and find one that gives you what you want. They were simply brilliant for my application. I did use some filter capacitors on the output. They don’t get hot, take up very little space on the PCB and make EE work very simple for the rookies like myself.
Here’s a model number that will give you 3A: TSR 3-1250
Yep! That’s the downside to linear regulators. The upside is they’re cheap, and if you’re just converting voltage for something small (like the Photon by itself) then the waste isn’t a big deal[*].
[*] unless you’re running on battery, then you almost always want to be as efficient as possible.
Thanks I just bought this one: https://amzn.com/B00BYTEHQO
I’m using a sla battery so I don’t want to waste power.
The unit you bought says it has a max current of 1.5 amps.
Here is a tiny and efficient 5A to 5v output regulator that would also work and give you a little more power to add more neopixels if you desire in the future.