The project I'm working on requires 24VDC to drive pneumatic solenoids. I have a 24VDC regulated power supply rated @ 1.9A which should be enough to drive all the solenoids and the BBB arduino. I am using the standard 7805 to regulate the 5v for the arduino and that dude is getting real hot. I measured the current going to the circuit beyond the 7805 hovering around 200mA when all the components that can be engaged at once are under load. I figure with the 19 volt drop @ .2A it would be dissipating 3.8 watts in heat. I'm not sure what this would work out to in degrees but with a heat sink bolted to the 7805 it gets hot enough to sizzle when I lick my finger and touch it. (no comments on the safety of that please.. lol) I checked the datasheet on the 7805 and see that it can take up to a 35v input and source up to 1A which I am well within. I was thinking about dropping the voltage with a 7812 then going to the 7805 and bolting them to the same heatsink, but am not sure if that will solve the problem (either way it's got to dissipate 3.8w right?). I was reading here: http://arduino.cc/forum/index.php/topic,61557.0.html
that I could use a different type of 7805 that is capable of sourcing 2A but don't know if that would help either. I also found this: http://www.dimensionengineering.com/DE-SW050.htm
but it's kinda expensive and I am trying to keep costs down as much as possible because I'll be building several of these units.
I really don't want to have 2 separate supplies for the project as outlet space is valuable in it's environment.
I'm hitting a brick wall at the 11th hour here and cant use a fan because it would put me too close to the current limitation of the supply and make the project box too big. If anyone has any suggestions it would be greatly appreciated. It would be real nice if I could plug mains 110 into the thing and transform the voltage with internally, but don't really have alot of experience with that yet.
That switching regulator would probably be a better solution - but I have to ask what kind of heatsink are you using? If the heatsink is getting that hot, it's probably not large enough; you might want to investigate buying or building a larger heatsink (look around for companies that sell alluminum heatsink extrustion profiles if you want to cut your own); you may also need forced cooling (ie, a fan). You also didn't say which 7805 you are using - that is, what case style? For what you are trying to do, I would go for TO-3 mounted to a larger heatsink, with a small fan providing forced cooling if the heatsink wasn't enough. You can probably get by with a TO-220 cased 7805, but the heatsink will have to be fairly beefy. You might find that the cost of the larger TO-3 7805 and/or heatsink and/or fan may end up being close in cost to that switching regulator, so price things carefully...