Search results

  1. audioguru2

    0-30 Vdc Stabilized Power Supply

    U2 gets very hot if the pins on the driver transistor are connected backwards because then the transistor operates like a simple series diode. Maybe you built the defective original version that used the old 2N2219 driver transistor that fails when it gets too hot and it is difficult to keep...
  2. audioguru2

    0-30V Stabilized Power Supply

    I am glad to help you but I am not a SIR, instead I am just an ordinary cool dude. I think a SIR was knighted by the Queen of England.
  3. audioguru2

    0-30V Stabilized Power Supply

    The pot is supposed to be a linear pot. You are probably using a pot with a logarithmic audio taper (used as a volume control). A pot with an audio taper has an output level of about 1/10th or 1/20th when it is half-way.
  4. audioguru2

    0-30 Vdc Stabilized Power Supply

    The original project has many errors and does not work properly and is not reliable. That is why this thread and another thread recommends modifications. R7 senses the output current. It is 0.47 ohms and with 3A it produces 1.41V across it which is fed to the inverting input pin 2 of opamp U3...
  5. audioguru2

    0-30V Stabilized Power Supply

    Yes because each output transistor has half the total current then their current gain is higher so the BD139 driver uses less current and is cooler. Even the opamp that drives the BD139 will use less output current and will be cooler.
  6. audioguru2

    0-30V Stabilized Power Supply

    One fan can blow cool air into the heatsink and the second fan can blow hot air out. We don't know if the fans can cool the output transistor well enough. That is why the improved version of this project has TWO output transistors to share the heat.
  7. audioguru2

    0-30V Stabilized Power Supply

    With a +32VDC supply and a 3A load, the voltage across R7 reduces the output voltage 1.41V. The maximum output of the TL081 opamp U2 is +29.1V but it could be as low as +27.6V. The maximum output of the 2N2219 driver transistor Q2 is +28.1V but it could be as low as +26.3V. The maximum output of...
  8. audioguru2

    0-30V Stabilized Power Supply

    When the original circuit has a 24VAC/3A transformer then the transformer can supply 24V x 3A= 72VA. But 24V rectified produces 24V x 1.414V (-2V for the rectifier bridge) which is +32V. But the circuit needs at least 40VDC instead of only 32V so the voltage from the original transformer is also...
  9. audioguru2

    0-30V Stabilized Power Supply

    The original version has many errors that cause it to be unreliable and not meet its specs.
  10. audioguru2

    0-30V Stabilized Power Supply

    I selected MC34071 or TLE2141 opamps because their inputs work at their negative supply voltage (0V here) and their outputs go down close to their negative supply voltage, and they are available almost everywhere. The first opamp you guessed about will not work. I didn't bother looking at the...
  11. audioguru2

    12v to 230 volts dc with voltage doubler circuit its possible?

    You forgot to attach the schematic. I show it with transistors that do not do much and with the 555 without added transistors.
  12. audioguru2

    0-30V Stabilized Power Supply

    Some of the circuit uses a -1.3V negative supply. It is made from a few parts. The entire circuit can have an output of 0V to -30V if you connect its + and - outputs in reverse so that the +30V output is used as ground and the 0V output is used as 0V to -30V. Many people have built two of this...
  13. audioguru2

    0-30V Stabilized Power Supply

    No. The trimpot is adjusted only one time for calibration. Adjust the trimpot for an output of exactly 30.0V with the coarse and fine pots set to maximum. The 1k fine pot is connected in series with the coarse 10k voltage setting pot P1.
  14. audioguru2

    0-30 Vdc Stabilized Power Supply

    The 6th page shows the username Picmaster who did it.
  15. audioguru2

    0-30 Vdc Stabilized Power Supply

    A few people designed pcbs for this project but I did not save them.
  16. audioguru2

    0-30V Stabilized Power Supply

    You made the 5A version of the latest circuit. The transformer must be 28V at least 200VA and the heatsink for the output transistors must be huge and maybe have a cooling fan. Most ordinary inexpensive multi-meters can accurately measure the load current.
  17. audioguru2

    FM TELEPHONE BUG

    The output power of that simple lousy circuit is almost nothing.
  18. audioguru2

    newbie questions

    I can't find a datasheet for the motor so I don't know its maximum current. The current will probably be too high for a potentiometer )it will burn up) and also too high for an ordinary little 9V battery (it might last for only a few minutes). An electric motor needs a high current to begin...
  19. audioguru2

    0-30V Stabilized Power Supply

    I think a large knob should be used for adjusting the voltage so you can see where it is and adjust it fine or coarse. If you add a fine adjustment pot in series with the coarse adjusting pot then one pot will frequently be at its end.
  20. audioguru2

    0-30V Stabilized Power Supply

    Your 28V AC transformer might produce 30VAC when it has low load current. 30V AC produces 42.4V peak. The rectifier bridge reduces it to 41.0VDC. Your 45V is a little too high but is OK for opamp U3 if the 10V zener diode that feeds it is not connected backwards. The cathode of the zener diode...
Top