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  1. audioguru2

    0-30V Stabilized Power Supply

    Then your transformer is very cheap with low quality. I have a Chinese 9VDC wall-wart that measures 18.5VDC without a load. At its rated current its output is 9VDC but with a lot of Ac ripple and boy-oh-boy it gets HOT! A Hammond power transformer has good spec's. Rated for 30VAC its output...
  2. audioguru2

    0-30V Stabilized Power Supply

    U2 is the only opamp with an input offset voltage adjustment. You said that the adjustment doesn't work unless U2 has a -5.6V supply. Then the total supply for U2 is too high.
  3. audioguru2

    0-30V Stabilized Power Supply

    If the negative supply is higher than 1.6V then the total supply for opamp U2 is higher than its absolute maximum of 44V when there is no load or a low current load.
  4. audioguru2

    0-30V Stabilized Power Supply

    Most opamps have an input offset voltage that causes the output to be a little away from the voltage it is supposed to be. RV1 is adjusted so the output is 0V when the proect is set to 0V.
  5. audioguru2

    0-30V Stabilized Power Supply

    Maybe your opamp u3 has a high i9nput offset voltage that needs to be adjusted to near zero. Q3 is simply an on-off switch. The opamp that drives it could be defective since without negative feedback its gain for DC is supposed to be nearly 1 million times. You are correct. The positive wire of...
  6. audioguru2

    0-30V Stabilized Power Supply

    The original schematic had a useless D10 from the base of the driver transistor to the output. I deleted it from my schematic but it is still on the parts list by mistake. The 10V/1W zener diode is on my latest 3A schematic (March 11/09) but it does not have a "D" number. It is D12 on my latest...
  7. audioguru2

    Sallen key problem stability

    A second-order Sallen and Key Butterworth filter is supposed to have a gain of 1 (a follower) when one component is double the value of the other or have a gain of about 1.6 when the components have equal values. DO NOT try to have a gain more than that, add an amplifier instead. There are...
  8. audioguru2

    0-30 Vdc Stabilized Power Supply

    A diode has a forward voltage drop of 0.7V only at one temperature and at one current. Its forward voltage drops as its current heats it and its forward voltage changes if its current changes. Simply look at the datasheet of a diode to see how much its forward voltage drop changes. The output...
  9. audioguru2

    0-30 Vdc Stabilized Power Supply

    Each output transistor needs its own 0.33 ohm resistor in series with its emitter so that they share the current. Yes an output diode is needed. Only oner diode is needed. When a diode is added in series with a regulated supply then the voltage is not regulated well anymore.
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    He must be using liquid nitrogen and a huge fan to cool his single 2N3055 transistor. Some people said that the output voltage does not drop to zero volts when there was an voltage then the voltage was reduced. It is because the electrolytic output capacitor C7 has "dielectric absorption". They...
  11. audioguru2

    Current monitor/sensor

    I do not know why you are doing things completely differently to the circuits in the datasheet of the IC.
  12. audioguru2

    Please help me with planning circuit!

    It is simple to use a quad opamp as 3 or 4 comparators. A stable reference voltage can come from a biased zener diode. The inputs to the opamps come from resistor voltage dividers. Add some hysteresis to prevent blinking at the threshold voltage. I recommend a quad opamp instead of an LM339...
  13. audioguru2

    0-30V Stabilized Power Supply

    Your transformer is rated for (25.5V x 3.6A)= 91.8VA. The circuit works from rectified AC and the peak voltage is (25.5V x root of 2)= 36V. Then the transformer is overloaded if the output DC current from the project is (91.8VA/36V)= 2.55A. The rectifier bridge reduces the output 2V and ripple...
  14. audioguru2

    0-30V Stabilized Power Supply

    I never recommended using the "A" version of the opamp and I don't remember if anybody else did. The difference is so small that you will not notice the difference. Instead of ordering an expensive custom-made transformer with 2 windings, simply use 2 ordinary transformers. This copy of my...
  15. audioguru2

    Current monitor/sensor

    Use Ohm's Law and simple arithmatic to calculate how many thousands of Amps will try to flow.
  16. audioguru2

    Current monitor/sensor

    I don't know if anybody makes a Low Side current sensor. It would be easy to make one.
  17. audioguru2

    Silicon chip micromitter fm stereo transmitter.

    No. Many fairly inexpensive FM stereo transmitters are available.
  18. audioguru2

    0-30V Stabilized Power Supply

    The circuit is already updated in the forum but not in the project. It uses parts that are common in North America, Europe and Australia. Go to www.farnell.com and click on the flag of your country. They have warehouses of electronic parts all over the world.
  19. audioguru2

    Silicon chip micromitter fm stereo transmitter.

    I don't think Rohm makes the excellent FM stereo transmitter ICs anymore. The Micromitter was published a fairly long time ago. (2005?) Its audio performance spec's were excellent.
  20. audioguru2

    0-30V Stabilized Power Supply

    I can't open your RAR compressed file because it has errors. Why not post the schematic as an ordinary PNG file?
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