I'm not much of an electronics person. I'm following the diagram for the switched electrobus at http://bit-tech.net/article/52/5 I was unable to find a place that would sell that particular suggested regulator in anything besides large bulk amounts here in the states. So I was wondering if this regulator is comparable: part # LM1117T-ADJ @ http://www.national.com/pf/LM/LM1117.html (the spec sheets are there) I also was wondering if I could hook up more than one fan (two to be exact) to a single switch/circuit or if that'd be too much. Thanks.
The LM1117T-ADJ is pin-compatible with a 317T, and, apart from the 800mA limit, would be a better choice in any 317T fan control circuit. I'll use the excuse to pimp mine . Note the two caps should be increased to 10uF and 100F for a LM1117T as shown on the datasheet. The max output from 12v input would be 10.8v, about 0.5v better than a 317T, but the Micrel chips go a stage or two further, and you could get 11.8v or so. They do a few fairly similar, so look out for MIC29152BT (1.5A) or MIC29502BT (5A) pin-compatible with the 3A MIC29302BT macroman used, or the MIC29372 (750mA) or MIC2941 (1.25A) which are not pin-compatible (& don't have the shutdown feature) but are a bit cheaper. You could add the switching and indicator led to any controller, using the yellow 12v direct line from the controller input and the olive variable line from the controller output. Two or more fans would be OK providing their total current draw doesn't exceed the limits of your control chip and its heat-sink - that's the weakest link.
Thanks cpemma, your page on choosing the correct heatsink was extremely helpful I did manage to find a place that will sell the micrel regulator recommended in the article. It has a 3A current capability, I'm assuming that's enough to run two 80mm fans together just fine on one circuit, correct? I had a heatsink I'd gotten off case etc.'s site awhile ago that they recommended for their LM350 setup so hopefully it's good enough (they didn't list specs on their site, but the heatsink is pretty large...about 50mm by 25mm). I took the LED leg out of the setup as I do not need it. The only other question I have is with one of the resistors. I have a bunch of 33K resistors already, as well as a 470ohm one (which I shouldn't need since the LEDs were taken out). But what is R2 in the diagram, the one listed as 4K3? Can anybody tell me a comparable resistor to that or some sort of specs for it? I'm in the states, I'd like to be able to get it from radio shack or mouser or something.
4K3 translates to 4.3 kohms for us USAnians. Eight of your 33 kohms in parallel would be pretty close...
ahhhh. heheh, well I feel dumb figured it was something like that. oh well. thanks again guys! (told ya I was a complete electronewb!) I WILL GET THIS THING BUILT IF IT TAKES ME FOREVER! Heheh. meanwhile, I'll just keep asking stupid questions
hmm.... well 4.3k seems to be a slightly harder value to find around here. Radio shack has 3.3 and 4.7 in both 1/4 and 1/2 Watt. they also have 3.9k in 1/2W. would any of these work as a substitute?
I'd use a 4k7 in that circuit. The output is 1.24* (1 + Rt/Rb) volts Rt = resistance above the wiper, Rb = resistance below the wiper So max, Rt = 33000+10000 = 43000, Rb = 4700, Vx = 12.58v & min, Rt = 33000, Rb = 10000+4700 = 14700, Vn = 4.02v You won't get 12.58v with a 12v supply, but it will get you to the top limit. A 4k3 would (theoretically) go up to 13.75v which gives you a bit more leeway if all the pot and resistor tolerances are the "wrong way".
