rocketPack

right... that'd be the first thing I learned in electronics class, except that I don't have a 3v power supply, nor the interest in buying hundreds of resistors of various values. I was looking for something more or less.... usable.

Same paramaters, 3v. I didn't mean "out of the picture" entirely, I just meant a fixed voltage, constant current. Anyway, amperage would also be the same... minimum adjustment of down to around 25 or 50mA (or less) preferred, and it has to go up to at least 750mA. Anything more is fine, I just wont be using it. The resistance will vary a little bit as it heats up, like you'd expect. The circuit is a diode laser, by the way - so it's obviously going to sink as much current as it can find without some kind of limit. Thanks for your input!

Well, I tried pricing out the ckt that Ante mentioned, but it's coming out at $38 before you count a proto board and a box + wiring (just the components themselves), which is out of my price range. I was wondering though - all I really need is a stable, regulated current supply at 3v. Does that make things any easier if you take v. adjustment out of the picture and just focus on obtaining a stable current supply? Well, I imagine it does... I did some googling and I didn't come up with much. I tried to use EWB to simulate using a voltage regulator set for constant voltage feeding into another set for constant current. It did not work well... at all. I can't remember which one I was using (perhaps something similar to LM117?) but I followed the manuf. data sheet's "typical application" and everything. Any ideas? I really appreciate all your help!

So I'm told... I'll show you what I did: I googled "LM2575", and found this result: http://www.national.com/pf/LM/LM2575.html I went there and filled out the " LM2575 WEBENCH&#174; Custom Design/Analyze/Build It/Test It" box with my exact specs, and then it said I could not achieve those specs with the LM2575, but I could with the LM5010. So I went to the LM5010 page and did the exact same specs, and it told me exactly what to buy, a schemat., etc. My settings were: Vin MIN: 8v Vin MAX: 16v Vout: 3v Iout: 0.75A The output is a 676kHz PWM signal @ 2.25W max. Do you see an issue though? It looks to me like the Iout is maintained by the feedback and the parallel resistor/cap, but I'm no expert at this stuff. If you see an issue let me know before I hook expensive stuff up and 'let the smoke out' :P Thanks! :) ----------- Edit: Upon re-reading your question, it seems you might be asking more about the adjustability - on that matter, I don't know how easily it can be adjusted, honestly. Like I said, I think it has to do with the parallel resistor/cap and the feedback circuit; do they make super low resistance, high power pots at decent prices (<$5)? If someone could explain the circuit to me a bit better (I'm only slightly able to understand it) that would be good too. I don't mind doing the leg work, but I need to know at least a little bit before I can do anything useful. I should also mention that EWB doesn't have an LM5010 or any other IC that has the same footprint (well, honestly, I didn't look very hard) so I took some other IC and renamed everything; that's why there is an extra pin...

Hey, I wish I'd seen that last night... :-X anywho, I ordered a 'sample' of a LM5010, their website drew me up a schematic and listed components and stuff so I bought them all from mouser (only about $12 + $11 for the 'sample'). Let me know what you think of this circuit, it looks very well regulated and filtered so it should be a good starting circuit (money is tight so I imagine this is about as good as I will get for this $$$). Opinions? I can still make adjustments if necessary! Link to FULL SIZE version (1086x445, 180kb): Sorry for the size, I just got a new widescreen monitor so I've got 1680x1050 pixels to play with... but I forget that not everyone has ;D

I googled the LM2575 and I found an amazing feature of national.com - I told it what I wanted from my power supply, and it picked all the components, made a schematic, and even ran an analysis for me! This is incredible! You definately gave me a 'push' in the right direction... thank you!

Hello! I am trying to build a low cost power supply (driver). It needs to be current limited (adjustability is good). It's going to be used to operate an optical device so regulation based on feedback from a photodiode would be superb. I've looked around at a lot of circuits but none seem to fit the bill quite right. Perhaps I can modify one, but I want to see what ideas you guys might have. The specs are: Voltage: 3v constant Current: Up to 750mA max required The input is still up in the air - but it would be highly preferred if it were somewhat 'flexible'. For example, I can use a 12v DC power supply but it's not going to be a rock solid 12v. I'm also considering 120VAC but using an already regulated and limited supply (such as a 12v one like I have) seems safer, easier, and more ideal. Here comes the hard part... It would be really nice if the unit could produced a high speed pulsed output, somewhere in the 50kHz range. Other features: - Soft start (for equipment protection) - Photodiode feedback control (like I mentioned earlier) Constant output is probably tolerable, however, and it can be done without the feedback control as well, though less ideally. I've looked at several dozen circuits and they all seem to have problems in my specific application. One thing I considered was this: http://www.mouser.com/index.cfm?handler=displayproduct&lstdispproductid=776079&e_categoryid=100&e_pcodeid=65253 My only problem really is finding a way to accurately and reliably control current; I want to avoid a simple 'put a resistor in series' approach. If anyone has links, suggestions, or reference designs I could work from I'd be very greatful. Thank you!

Hello, I'm in the process of building a new (small) aquarium and I'm always bothered by lighting problems. I had this idea... Have Red, Green, Blue, UV, and IR LEDs in groups in a large array over the tank to produce realistic lighting. The first problem is, of course, where to find the appropriate LEDs such that I don't have to use hundreds of them to produce white (since LEDs seem to have a narrow wavelength range of output, I'm guessing I'd need a good 20 different types of each R/G/B led to produce something white). Are there broad spectrum LEDs available? Or am I better off using white/uv/ir LEDs? Ok, so now the plan to control the LEDs... What I had in mind was MOSFETs (or transistors... I don't know much about MOSFETs but from what I can tell they handle large currents better than regular transistors) driven by photoresistors. My original plan was to put the photoresistors outside where they would receive full sunlight, and place each one underneath a bandpass light filter corresponding to the wavelengths of light that the photoresistor (PR from now on) controls. For example: PR with ~800nm+ filter on it attached to a source and fed into the gate of a MOSFET. A source attached to the source and drain with infrared LEDs attached to it. When the sun comes up and produces large amounts of infrared light, the PR will drop its resistance and in turn the MOSFET will sink a large current to the IR leds to reproduce the lighting conditions of outdoors. That's the basic principle, simply repeat for each spectrum of light... This has many other wonderful benefits such as: completely automated, never have to remember to turn stuff on and off; no need to worry about re-setting the clock on timers for changes in daylight or when the time changes; the ability to mimmic seasonal changes in lighting as well as weather related changes; the ability to mimmic moonlight; and overall the ability to provide the fish with the most realistic and natural lighting conditions possible to help them live a happier, more healthy life, as well as providing plants with essential light to help them grow. My real problems are: - Choosing the proper components; I'm new to MOSFETs and I only have limited experience with transistors (I'm good at setting them on fire with a 9v battey too - I have the scorched breadbord to prove it :)) - Locating LEDs that produce a sufficiently broad enough spectrum to limit their quantity to less than about 211 bagillion. - The dynamics - I know that MOSFETs (or any transistor for that matter) are not linear, and I don't mind my light deviates from the sunlight, I just want it fairly close. I guess the question here is how to calibrate and configure it so that things work properly and reliably. This is probably the most complex problem. I really need a push in the right direction. I think starting with the LED selection is best, because I can't pick a MOSFET or any other power related component until I have a clue what my power needs will be, which is obviously dictated by the LEDs. After I get the LEDs sorted out, I'd need help figuring out how to chose the proper MOSFETs, since I'm not entirely certain what all the terms on a datasheet refer to (such as Gate-Source breakdown voltage) - I have a clue what it's referring to, I just don't really know how these things affect it's performance and what I need to do to stay within those defined limits. If anyone's got something to get me started, advice, links, examples, kits, suggestions, etc., I'd be very, very greatful to hear it! Thanks a lot, -Scott P.S. My real experience in electronics is limited to about 5 classes I've taken recently at city college (over the last 3 semesters or so). I'm no engineer, but I am quite capable of learning as I go, and I am fully aware I will need to learn plenty to finish this project, but right now I'm more of a fundamentals-wise person and less of an expert.