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This is a 7805 voltage regulator, apparently a very common item produced by the millions. Again, I leave out values of things like capacitors. This complicated looked circuit (for me) took a while, as I didn’t grasp the fact of the common ground.
Theory:
Any voltage from 7.5 to 30 Volts fed into the 7805 will emerge as a steady 5 volts, with the excess being radiated away as heat. The capacitors are to smooth out any fluctuations in the input and output currents, or voltages. The input is a big capacitor, the output is a small capacitor. I don’t know why.
Practice:
The 7805 has three pins, the middle one being a common ground. To me, this meant the voltage came out of the regulator “upside down”, that is, the positive lead is the opposite side of the ground from the input lead. Look at it for a second, you’ll see what I mean. I don’t know the symbol for a voltage regulator, but it sort of looks like what I drew, with the little hole for mounting a cooling fin for larger voltages.
Conclusion:
This circuit worked out perfectly. The input voltage was 12.3V and the output was 5.0V although the specs said this could vary between 4.75 and 5.25. It was bang on. I even tested it with the current direction diodes from experiment 001. I’ve left it installed on my tiny breadboard as it only takes up three rows of pins.
Update 2012-04-27
I finally built my own version of this handy circuit. Looking back, I realize the absolute need to combine theory and practice in short, coordinated settings. Building small projects like this is more than important when getting started. Here is a photo of the circuit shown above, but with an LED added to show when it is operating. The board rests on a small piece of dry sponge to make it handier when I'm working with bare wires.
Now when I say short learning sessions, I've found it best to go out and build something almost as soon as you learn the theory. This tiny circuit taught me more than any of the $60 text books I studied at first. I grasped the concepts, but until I built this circuit, it was a struggle to get anything to work. I'll write out the things I believe were most important. First, here is a photo (I still don't have a macro camera).
A) notice the tight grouping of the components. This is a weird departure from the layout used on your breadboard. When you flip the circuit over, you must learn to think "backwards" to keep organized, especially with parts that are polarized.
B) you can't see the reverse side, but how strange that there is no convenient way to make the connections. You can solder connecting wires, which is a messy process more trouble than it is worth. I bent the component leads together wherever possible, and used blobs of solder where possible. There is a trick to doing this right and you can't learn it from a lecture. Just do it.
C) those blue connectors were an afterthought. I was not sure how I would use this circuit, but these screw terminal type connectors let me use solid wire, stranded wire and standard breadboard connector pin wires. But I would not use them again, since you always have to hunt for a small slot screwdriver. Again, learn it by doing it.
D) this circuit was one of around a dozen separate "parts" I constructed and now use as modules for other experiments. This is wiser than building anything complicated on a larger board, and building this first 7805 power supply taught me that. The most expensive component was that yellowish capacitor, which seems to make absolutely no difference in the performance.
E) you gain an appreciation of what things cost. Some well-funded individuals may disagree, but if you are on a budget, you learn to work better when building things like this circuit. Sometimes you learn that a ready-built item already exists and costs less, but you continue anyway for the learning. I've yet to see a major author that spells out this extremely important factor--the average guy will always run out of money before he runs out of project.
Keep at it, one year later I can solder just about anything successfully on the first try. And this little gizmo is where I started.
It's kind of grainy, but here is a photograph of the club using some of the little circuit boards I made like the one above. Shown here is a 555 timer circuit and a transistor switch being to used to test the operation of a store-bought car stereo board. Note both are built on pre-fab circuit boards like the kind you buy at the Shack. See also the 12V motorcycle battery in use. It cost $35. But you'll quickly tire of dry cells when you want to get some serious work done.
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