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  1. BobK

    Guitar Pedal Project!

    Scratching my head over why a guitar effect pedal would take 300ma. Bob
  2. BobK

    Choice of topology for LED Driver?

    Why not use a chip designed to do exactly what you want? This one meets all of your specs and can drive your 12 LEDS as a single string with constant current. http://datasheets.maxim-ic.com/en/ds/MAX16833-MAX16833E.pdf Bob
  3. BobK

    Op-amp behaviour confusing for an amatuer

    You clearly did not understand my post. I did not say that no op amp circuits require dual supplies, I said that no op amps require dual supplies. With only 2 power connections, how can the op amp tell the different between a dual 5V supply and a single 10V supply? The reason dual supplies...
  4. BobK

    need help on small solar panel project.

    Well, you could use your solar panel + a DC-DC converter to charge a 12V battery, then run the fan off the battery. It would take about 20 hours of charging to run the fan for 1 hour though. Bob
  5. BobK

    Charging NiMH battery

    Read the charging section in this article: http://en.wikipedia.org/wiki/Nickel%E2%80%93metal_hydride_battery Your best bet is to trickle charge at < .1C which would be about 20ma. Use a 5V supply and then calculate a resistor to limit the current to 20ma, i.e. (5V -3.6V) / 0.020 = 70Ohms...
  6. BobK

    Can a step-down transformer be used as a step-up transformer?

    An option would be to get an old microwave oven transformer. They put out about 2KV from mains input. You could drive it from a variac to get 1KV, or if you could find one designed for 240V you could run it off 120V. http://wiki.4hv.org/index.php/Microwave_oven_transformer Bob
  7. BobK

    Can a step-down transformer be used as a step-up transformer?

    The inductance is not enough to limit the current and it burns up. Bob
  8. BobK

    Lamp Circuit - Need Help

    For safety I would use an opto-isolated triac to build this. That way the low voltage electronics are not connected to mains. Bob
  9. BobK

    Can a step-down transformer be used as a step-up transformer?

    I hope you noticed this line from the datasheet. • Frequency range from 40 to 80 KHz Don't go putting 60Hz AC on it! Bob
  10. BobK

    Op-amp behaviour confusing for an amatuer

    I have yet to see an op amp that requires dual supplies. Since they typcially have only V+ and V- power connections, how would they know whether you are using dual supplies or not? The only consideration is what range of votages you need at the output. If you need 0V, you will need dual...
  11. BobK

    Oh what to do with a Tetrode tube????

    Umm, a tube with 4 pins is not a tetrode. It needs two pins for the filament, so it is probably a diode. Bob
  12. BobK

    Oh what to do with a Tetrode tube????

    A tube marked with "short" sounds pretty ominous to me. Bob
  13. BobK

    Heat Issues with LM732 Power Supply

    This is a linear regulator. Any linear regulator is simply wasting the excess power as heat. The power wasted is (Vin - Vout) * Iout. If you want a regulator that does not waste power, look into switch mode regulators. Bob
  14. BobK

    More efficient SMPS IC?

    Not to mention that diodes are no more efficient at dropping a voltage than a resistor is. You can produce a low voltage supply from mains voltages by using a capacitor to drop the voltage, which is more efficient since the capacitor dissapates no power. Bob
  15. BobK

    Can a step-down transformer be used as a step-up transformer?

    Hexreader, With 1/10'th the turns, the secondary should draw about 10 times the current that the primary would when connected to line voltage. However, it also should be able to handle 10 times the current. No? Edit: No i am wrong, the inductance is proportional to the square of the...
  16. BobK

    Obtaining 250V, 500mA

    Well, a fixed input voltage makes it a lot easier. I would look up inverter circuits in the power range you are interested in. You will find them that operate off either 12V or 24 volt DC. Tweak the circuit (probably just change the transformer) to get the voltage you want out. Then just use...
  17. BobK

    New to Electronics

    Oh, sorry, I was only looking at the later question. Bob
  18. BobK

    Obtaining 250V, 500mA

    A power supply of your specs would not be easy. At 2V input you are talking about 62.5 Amps if the efficiency was 100%, more like 75 Amps in the real world. You cannot scale this up from a supply designed to give 5ma, the design criteria are completely different. Try to find something...
  19. BobK

    New to Electronics

    I think you answered the wrong thread, Steve. Bob
  20. BobK

    Basic theory of DC > DC (Boost)

    Inductors are probably the most difficult of the basic electronic components to understand. Inductors resist a change in current. And to do this, they change the voltage across themselves! So when, as Steve said, you remove the source of a current in an inductor, it will raise it's voltage to...
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