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.
It's the TO-220 package and the heat sink is wimpy, I scavenged it off a old satellite TV board. I found this: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=102-1715-ND which isn't too pricey and it is a drop in for the 7805 TO-220 so I wont have to modify the board layout (done that way too much in the past week, hand rerouting is getting tedious) and I really need to get these board gerbers sent out to get them back in time to be able to solder up hundreds of components. (70+ per board * 5 boards, ugg). Sure do wish I could use some type of 7805 TO-220 though, would save $9 per board.
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