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  1. audioguru2

    0-30 Vdc Stabilized Power Supply

    Sorry, I got mixed up about which opamp belongs to which opamp of the duals since all the other circuits used single opamps so they stay cooler. Your circuit has a -3V negative supply and your opamps worked. But the datasheet for the old TL082 shows an input common-mode limit of 4V max, not 3V...
  2. audioguru2

    0-30 Vdc Stabilized Power Supply

    Your V3 design is very nice. I noticed that on your V2 design the output of opamp IC1A cannot go low (because it is missing a negative supply) to regulate the current and things might burn up. The old TL082 opamp has the "Opamp Phase Inversion" problem: If an input voltage is too close to the...
  3. audioguru2

    0-30V Stabilized Power Supply

    Ohm's Law says that  the current in 71 ohms when it has 30V across it is (30V/71 ohms=) 0.4225A. For a current of 3A then the 71 ohms needs (3A x 71 ohms=) 213V across it. If you want 30V and 3A then the load must be (30V/3A=) 10 ohms. Ohm's Law uses simple arithmatic.
  4. audioguru2

    0 30V power supply

    Yes because it is an old transistor that is difficult to cool and it is overloaded in the original circuit. Use a BD139 REAL power transistor instead with a medium size REAL heatsink. The voltage at the output pin 6 of U1 is supposed to be 11.2V if you use a 5mA zener diode. The maximum output...
  5. audioguru2

    0-30 Vdc Stabilized Power Supply

    Use a transformer rated for 2.8A AC output. Change R7 to 0.68 ohms/5W. 2.8A x 28V= 78.4VA. The power in each 2N3055 when the output voltage is low or shorted and the current is 2A, is 38W.
  6. audioguru2

    0 30V power supply

    The negative feedback for U1 uses a 5.6V zener diode. R5 and R6 have equal values so the voltage gain of U1 is 2 which makes the zener current (also the current in R4) 5.6mA and makes the voltage at the output 2 x 5.6V= 11.2V. Yours has a voltage too low probably because you used a different...
  7. audioguru2

    0-30V Stabilized Power Supply

    Yes that is my latest schematic and parts list. I designed the fixes and would have posted it as a project but I have never made it because I do not need it. Somebody who has made it and tested it should post it as a project.
  8. audioguru2

    0-30V Stabilized Power Supply

    An ammeter has resistance so when it is connected in series with a load then it reduces the voltage to the load a little. Then the current in the load is reduced a little. Connect an accurate low value power resistor to the output then measure the voltage across it and use Ohm's Law to caculate...
  9. audioguru2

    Should MOSFETs be open all the way?

    I answered on the other website. The circuit does not make sense.
  10. audioguru2

    0 30V power supply

    Did you make the original 0V to 30V/3A power supply that has errors or did you make the corrected version discussed in the forums that works fine? The regulated 11.2V reference voltage is made from U1 and D8 that is fed to the voltage control pot P1. P1 feeds U2, Q2, and Q4 that form a power...
  11. audioguru2

    My Sound Level Indicator project

    I designed and made only one circuit over 7 years ago. It still works fine. My computer and digital camera were brand new and I was still learning how to use them. Here is the parts layout photo with red "Xs" where each stripboard track was cut and this photo has better contrast.
  12. audioguru2

    0-30V Stabilized Power Supply

    Maybe from 1.0A to 5.0A. Adjust it for 3.0A maximum when the current pot is at maximum and there is a heavy load or a shorted output. When the output voltage is low or shorted and the output current is 3.0A then the driver and output transistors get extremely hot. R7 (0.47 ohms) senses the...
  13. audioguru2

    0-30V Stabilized Power Supply

    The project can regulate the voltage if the current pot is set to a higher current than the current that is used, or it can regulate the current (by reducing the voltage). It cannot regulate voltage and current at the same time. Its MAXIMUM output current is supposed to be only 3.0A, and when...
  14. audioguru2

    0-30V Stabilized Power Supply

    The trimpot in the negative feedback of the output stage is adjusted for 30.0V when the voltage pot is turned up to maximum. The trimpot near U3 is adjusted for 3.0A when the load is drawing 3.0A and the current pot is turned up to maximum. Adjust the offset voltage trimpot for an output of 0.0V...
  15. audioguru2

    555 calculation in astable mode

    Didn't you look at the datasheet? It shows how to simply calculate the charge resistors, the discharge resistor and the capacitor.
  16. audioguru2

    0-30V Stabilized Power Supply

    A solderless breadboard frequently causes modern opamps to oscillate at a high frequency. Use a pcb instead. The peak voltage of the 28VAC or 30VAC transformer is 1.414 times higher which is 39.6VDC or 42.4VDC then the bridge rectifier reduces the positive supply to 37.6VDC to 40.4VDC. The...
  17. audioguru2

    0-30V Stabilized Power Supply

    You NEVER add a resistor in series with the power supply pin of an opamp. If you reduce the supply voltage of the opamps then the maximum output voltage of the project is also reduced. Then you do not need a high supply voltage.
  18. audioguru2

    0-30V Stabilized Power Supply

    Sorry, I made a mistake. I thought your tiny transformer was rated for 1.2W but instead it is rated at 1.2A. Then its maximum power is 18V x 1.2A= 21.6VA. Its peak voltage is 18V x 1.414= 25.5V so it is overloaded when your output current is more than 21.6VA/25.5V= 0.85A. The original circuit...
  19. audioguru2

    0-30V Stabilized Power Supply

    It looks like you made the defective old kit but used a tiny little transformer so the maximum output is 18.6V at only 48mA.
  20. audioguru2

    0-30V Stabilized Power Supply

    I answered this question on Feb 19: "Most people's problems with this project are ICs or transistors with their pins connected backwards. Double check the pins with the pictures in the datasheets." The pots set the output to 0V and 30.0V, a few mA to 3.0A.
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