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  1. audioguru2

    0-30V Stabilized Power Supply

    The current regulator opamp is not oscillating. Its output is saturated as high as it can go which is about +28V because it is not regulating the current so of course it shows the 120Hz ripple from the unregulated +39V, which is reduced to +29V by the 10V zener diode. The moment the current...
  2. audioguru2

    0-30V Stabilized Power Supply

    We cannot teach the basics of opamps in one post but here goes: 1) Everyone who modifies this circuit uses a different parts numbering system so I will describe the three opamps as the voltage reference circuit, the voltage amplifier and the current regulator. 1) The voltage reference opamp...
  3. audioguru2

    0-30V Stabilized Power Supply

    It slows down changes in the voltage regulation. Add a load then the voltage suddenly drops and when this capacitor charges then the voltage slowly comes up to normal. Disconnect a load and the voltage suddenly increases and when this capacitor charges then the voltage slowly comes down to...
  4. audioguru2

    0-30V Stabilized Power Supply

    C6 in the latest SIM circuit prevents the current regulator from quickly cutting back or quickly allowing more current. Then if the output is suddenly shorted the current in the circuit will skyrocket until the slowly ramping opamp can catch up which is very bad. Maybe the current sensing...
  5. audioguru2

    tda7297 pulsing output

    Since you bought it from Amazon then maybe the IC is a fake or maybe the circuit is designed wrong. Please provide a link to it. The output pulses? When it is playing loudly? Does the heatsink get hot? What impedance are the speakers? What is the maximum continuous current from the 18V power...
  6. audioguru2

    0-30V Stabilized Power Supply

    The very old LT1001A opamp is very slow like a lousy old 741 opamp. The TLE2141 is MUCH faster. You have C6 as only 33pF but it should be 330pF. Why does the circuit have C11? It is causing the current spike and maybe is causing the oscillation.
  7. audioguru2

    0-30V 0-3A Latest Data Discussion

    A 28V transformer might produce 29V when the project has no load. Then its 41.0V peak voltage is reduced to 39.6V by the rectifier bridge. It will be fine if the mains voltage is very stable.
  8. audioguru2

    0-30V 0-3A Latest Data Discussion

    Good point. Eliminate Q3, turn the polarity of the LED around so its cathode is at the collector of the new lower NPN transistor and its current-limiting resistor is between the anode of the LED and the +27.6V. Another good point but there is no problem. If the output is shorted then we want the...
  9. audioguru2

    0-30V Stabilized Power Supply

    Then you must replace the 10V zener diode with a resistor. I do not think U1 needs its power supply voltage regulated because a TLE2141 opamp has a minimum Supply-Voltage Rejection Ratio of better than 90dB so 2V of ripple causes an output of less than 62.5uV (typically less than 2uV) which is...
  10. audioguru2

    0-30V 0-3A Latest Data Discussion

    When the load current is higher than the current regulator setting and the voltage is set high, the "on" voltage spike is caused by the time it takes for the negative supply to reach a low enough voltage (-1V?) for the current regulating opamp to pull down the voltage feeding the voltage output...
  11. audioguru2

    0-30V Stabilized Power Supply

    In Canada we also have three wires, live, neutral and earth ground. I have seen electrical outlets wired wrong by drunk electricians or by homeowners who do not know how to do it correctly so the "earth" terminal is actually "live". Then if a person touched the metal chassis and an earth ground...
  12. audioguru2

    0-30V Stabilized Power Supply

    RV1 nulls the input offset voltage of the voltage setting opamp U2 so that the output is exactly 0V when the voltage pot is set to zero. Without RV1 then the input offset voltage of the opamp (if there is any) will cause a small positive or negative voltage output instead of 0V. But some people...
  13. audioguru2

    0-30V Stabilized Power Supply

    Did I calculate it wrong? 28VAC has a peak voltage of 39.6V and the rectifier bridge drops 2V to 37.6V and the capacitor ripple drops it to maybe 35.6V. if the current sensing resistor is 0.47 ohms then it drops 1.4V to 34.2V. Then the 0.33 ohm emitter resistor drop 0.5V to 33.7V so the output...
  14. audioguru2

    0-30V 0-3A Latest Data Discussion

    The MC34071 is no longer available in a through-hole package (it is only surface-mount now) so the TLE2141 opamp from Texas Instruments is used. I think a 24V transformer produces peak rectified voltages of 32V at 3A and ripple reduces the minimum voltage to about 30V. That is why the circuit...
  15. audioguru2

    cyberpower 375SL service manual?

    I agree that the battery might be bad. If it is lead-acid or Lithium then its life might be finished. Replace it.
  16. audioguru2

    Can I use a common ground

    Its datasheet says the relay is a Chinese "Songle" relay. What is that?? They cannot spell "single"? Its coil current is 120mA at 3V. I betcha the sensor cannot provide an output current as high as 120mA at 3V. Then the relay needs a transistor to drive it and the sensor drives the transistor...
  17. audioguru2

    Can I use a common ground

    You did not provide the coil voltage and its current of the relay and did not provide the output current of the sensor when its voltage is only 3V. The coil produces a voltage spike of hundreds of volts when the relay turns off. Usually a reverse-biased diode is connected parallel to the coil...
  18. audioguru2

    Power supply short circuit protection.

    The corrected latest version reliably regulates the maximum current to be 3.0A. Then an additional protection circuit is not needed. Buy name-brand parts from an honest electronic parts distributor, not cheap fake junk from ebay and the project will work fine.
  19. audioguru2

    0-30V Stabilized Power Supply

    I did not look at everything on Picmaster's schematic to see if it has any more problems. Liquibyte made a new thread showing the latest version of the 3A supply here: http://www.electronics-lab.com/forum/index.php?topic=39481.0
  20. audioguru2

    Power supply short circuit protection.

    Why was this garbage circuit posted as a project here? It is without an explanation of how to connect it and how it works. Maybe its author built the power supply but its current regulation did not work. Instead of asking for help to fix it in the forum then he posted this garbage circuit instead?
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