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Everything posted by ffrige

  1. Thanks a lot guys. I now put two diodes in parallel, just to make sure that nothing bad happens again...
  2. So... I finally managed to finish my variable power supply, but unfortunately it didn't last long. I used it to drive a DC motor and, as you guys suggested, I simply reversed the output wires to change direction. After just a few switchings the LM317 croaked. I imagine some inductive spikes from the motor were too strong for the poor regulator. (although I thought it had an internal protection...) What can I do to prevent this from happening again? The thing is that the output from the LM317 does not go to 0V ever. Which means that even reducing to minimum the voltage applied to the motor, this will always go nuts with a sudden input reversion. Do I need to disconnect the motor from the regulator before switching the polarity?
  3. MP, thanks for the answer and sorry if I was confusing. I guess I didn't want to use two different regulators since I don't need positive and negative voltage at the same time. But I need a switch to be able to flip the output somehow. If I can't do that with the ac voltage using only one regulator, can I maybe do that directly on the output? What kind of relay would I need to do this automatically? Thanks, ffrige
  4. Hi everyone! I saw there are several different projects for power supplies and I'm not sure what the real differences between them are. In particular, what is the difference between using a high current regulator (say lm317 or lm350) and using a low current one (lm723) with external transistors to boost the output current? Which design is cheaper? Also, what's the easiest way of getting +/- output voltage with the same current requirements? Do I need to double the trafo voltage or can I just flip the input to the regulator with a switch? Thanks in advance! ffrige
  5. Hi. I ran into the problem of subtracting two impedances. I thought I could solve it simply by putting the first in series with the negation of the second (using a negative impedance converter), but something is not working. Is it really possible, for example, to put a resistance in series with its negative equivalent and then read zero across the two with a simple ohmmeter? Or is the circuit more complicated? Thanks!
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