| Electronics > Beginners |
| transistors |
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| ledtester:
On the subject of transistors, when it comes to learning how to analyze circuits involving semiconductors, for the beginner/hobbyist I highly recommend either of these books - both by Albert Malvino: Transistor Circuit Approximations Semiconductor Approximations: An Introduction To Transistors and Integrated Circuits Used copies may be found on Amazon for cheap. They are very practical books with good worked examples. The Art of Electronics is excellent but kinda skimpy on worked examples - largely, I believe, because they expect that to be provided for by teaching assistants in a recitation class. |
| fourfathom:
--- Quote from: Jwillis on August 15, 2019, 10:40:56 pm ---I tried your flasher circuit and all it did was cook the transistors. So I took the liberty of redesigning the circuit to one that I tested and indeed works and it won't cook the transistor.I added notes but feel free to make any changes you like for different effects.I was to lazy to diagnose the problem with the first circuit. --- End quote --- This circuit has a problem too, in that when the NPN turns on there is no limit on the current from 9V+, through the LED, through the PNP emitter-base junction, through the NPN collector-emitter path, to ground. Perhaps there isn't enough base current into the NPN to drive things hard enough to cause problems, but I would like to seen some current limiting, probably at the PNP base. |
| floobydust:
OMG dusted off my 1980 Engineer's Notebook by Forrest Mims III. It was a real hoot building all that stuff, never had so much fun. The lamp flasher was also our high school electronics class "strobe" light project, where we made our own pcb and cut sheet metal for the enclosure. I later turned evil and made it drive a car ignition coil... It looks like it has a few weaknesses, like needing a resistor to limit current through the potentiometer so it does not smoke, the electrolytic capacitor polarity might be arguably flipped, and I would add a second resistor to limit base current for Q2. This sch is the corrections I have in mind. |
| tooki:
--- Quote from: Zero999 on August 15, 2019, 09:41:16 pm ---Finally please do a little image processing on photographed schematics. It makes them clearer, as well as saving bandwidth. (Attachment Link) --- End quote --- Your example image is very hard to read, whereas the OP's scanned (not photographed!) original is easy to read. So no, please don't do this! |
| Zero999:
--- Quote from: tooki on August 16, 2019, 06:53:52 pm --- --- Quote from: Zero999 on August 15, 2019, 09:41:16 pm ---Finally please do a little image processing on photographed schematics. It makes them clearer, as well as saving bandwidth. (Attachment Link) --- End quote --- Your example image is very hard to read, whereas the OP's scanned (not photographed!) original is easy to read. So no, please don't do this! --- End quote --- I admit it wasn't my best attempt, but I find the lack of contrast in the original difficult to read. More importantly I forgot to add the base resistor to Q2. |
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