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  1. audioguru2

    0-30V Stabilized Power Supply

    There have been many pcb designs for the various versions. The original pcb used parts that were too small so they overheated. Some of the newer larger parts do not fit on it. The latest schematic (REV 3) has calibration trimpots added.
  2. audioguru2

    0-30V Stabilized Power Supply

    If the output capacitor C7 is electrolytic then it has "dielectric absorption" which causes the output voltage to rise with no load if the project is powered or not. A film capacitor will not do that. An output load resistor can discharge a film C7 when the power is turned off. When the...
  3. audioguru2

    0-30V Stabilized Power Supply

    The original circuit had a few serious problems. It used TL081 opamps that need a 5.6V negative supply for their inputs to work properly and its absolute maximum allowed total supply was only 36V. The project used a 24V transformer which produced an unregulated +32V which is not high enough for...
  4. audioguru2

    0-30V Stabilized Power Supply

    C7 is an electrolytic capacitor on the output. electrolytic capacitors have dielectric absorption where they store a voltage for a while. Try using a film capacitor instead then adjust the input offset voltage trimpot on u2 for an output of 0v when the voltage pot is at zero. If the BD139 or...
  5. audioguru2

    4 rechargeable AA batteries to standard USB power line

    For many years, AA Ni-MH rechargeable battery cells had a capacity of 2500mAh, but they self-discharged in 1 month. In the past 6 years new AA Ni-MH cells have a capacity of 2000mAh to 2300mAh and hold their charge for 1 to 3 years (Sanyo Eneloop). Sony claimed a very high capacity of  3800mAh...
  6. audioguru2

    0-30V Stabilized Power Supply

    The output of U3 and Q3 should never turn the LED on dimly. Maybe if the current-setting pot is at minimum, there is no load and U3 has a fairly high input offset voltage then the LED will be turned on. R17 sets the amount of minimum current regulation so it can be increased to 47, 56 or 68 ohms...
  7. audioguru2

    0-30V Stabilized Power Supply

    U3 and Q3 are a switch that is on or off, never half-way. Maybe you used an opamp for U3 that is different from a TLE2141 or MC34071? I marked the current regulator circuit with notes that explain how it works:
  8. audioguru2

    0-30V Stabilized Power Supply

    You forgot to add a heatsink to the BD139 driver transistor. When the output is shorted then it will dissipate 1.5W if the output transistors have typical current gain or 5.5W if they have minimum current gain. Without a heatsink it is at its max allowed temperature with a dissipation of 1.2W...
  9. audioguru2

    0-30V Stabilized Power Supply

    U1 is simply an 11.2V reference voltage so it has nothing to do with current in the output. U3 is used as a comparator to sense the voltage across R7 which represents the output current and compares it with the voltage set by the current-settingh pot. If the sensed current is too high then the...
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    A 24VAC transformer voltage is too low. I guess some people have liquid nitrogen.
  11. audioguru2

    0-30 Vdc Stabilized Power Supply

    The original project is an old piece of garbage with many errors. It does not produce 30VDC at 3A and is not reliable. That is why I fixed it. We talk about the latest fixed version on this and on another thread here. Look through this or the other thread to find the latest parts list (Rev 3)...
  12. audioguru2

    0-30V Stabilized Power Supply

    Without a load a 28V transformer will be 29VAC and a 30V transformer will be 31VAC. The peak voltage of 31VAC is 43.8V and the bridge rectifier drops the unregulated DC to 42.4VDC. The absolute max allowed voltage for the latest recommended opamps is 44V. Your 57VDC is 14.6V higher than...
  13. audioguru2

    0-30 Vdc Stabilized Power Supply

    If the output voltage is set low, the load is shorted or draws 10A and the current-setting pot is set to 10A then the output transistors (six of them) will dissipate a total of 390W. How will you cool them? The driver transistor cannot drive six output transistors so it must be made stronger...
  14. audioguru2

    0-30 Vdc Stabilized Power Supply

    The MC34071 or TLE2141 opamps operate near their maximum allowed supply voltage (44V) with a transformer that is 30VAC. A 48V transmormer voltage is much too high so the opamps are probably blown up. The transistors also might be blown up. Resistors and capacitors too? Why did you try the...
  15. audioguru2

    0-30V Stabilized Power Supply

    It is my parts list and schematic. With a 3A load then U3 should begin to reduce the output voltage and light the LED if the current tries to get higher. I marked up the schematic to show the current regulator at 3A:
  16. audioguru2

    0-30V Stabilized Power Supply

    I can't read his schematic because it is fuzzy and has no contrast. If he draws the parts closer together then the schematic can have larger parts which will look clearer. Then he should increase the contrast. I guess that RV3 is a variable resistance trimpot in series with the current pot...
  17. audioguru2

    0-30 Vdc Stabilized Power Supply

  18. audioguru2

    0-30V Stabilized Power Supply

    It is simple to attach a schematic to your post: 1) During your reply, click on Additional Options. 2) Click on browse and locate the schematic's file on your hard drive. 3) Click on the file then click Open and it will be placed in the Attach box. 4) Post your reply then your schematic will be...
  19. audioguru2

    Blank screen when I try to reply

    Thanks, Mixos. I hope you have a recent backup copy.
  20. audioguru2

    Blank screen when I try to reply

    No, i did not send Mixos an e-mail or private message because I thought he should be reading "FEEDBACK/COMMENTS".
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