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  1. audioguru2

    Current monitor/sensor

    Your RC networks are lousy filters:
  2. audioguru2

    0-30 Vdc Stabilized Power Supply

    The output current is not shutoff when the current exceeds the current setting. Instead the current is regulated to drop to and stay at the setting: 1) Voltage is set to 20.0V and current is set to 1.0A. No load. The output of U3 goes as high as it can, D9 is reverse-biased and does nothing...
  3. audioguru2

    0-30 Vdc Stabilized Power Supply

     I think with a low output voltage at 5A then driver transistor Q2 will get too hot. I think the three 2N3055 transistors will also get too hot. Opamp U2 also might get too hot. 
  4. audioguru2

    0-30 Vdc Stabilized Power Supply

    The Rev7 schematic is titled 3A, not 5A. How will you prevent it from melting? If you use a supply for the voltage regulating opamp of only 33V then the project will not supply an output of 30V, it might supply only 25V at full current. That is why we use 44V rated opamps.
  5. audioguru2

    Fan Failure Alarm

    Can the wind from a fan push a wing that pushes on a changeover switch? Then when the fan is slow or it stops (even if its electrical power gets cutoff) the changeover switch changes the light from green to red. The switches must use diodes and resistors and DC to make an "OR gate". The DC from...
  6. audioguru2

    0-30 Vdc Stabilized Power Supply

    Use another opamp connected like U3 but with a 10k negative feedback resistor (or any other value if you need more or less gain.
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    I hate it when people copy a schematic and change all the parts numbers around. The original schematic has U3 as the current regulator, U1 as the voltage reference and U2 as the voltage regulator. I kept them on all my updates. Rev7 was drawn by Liquibyte and has U1 as the current regulator...
  8. audioguru2

    0-30 Vdc Stabilized Power Supply

    The output of opamp U1 must go negative in order for D9 to reduce the input of opamp U2 to near 0V when the output is shorted so that the output current is regulated.
  9. audioguru2

    555 dc motor controller

    Why don't you look at the datasheet that shows both darlington transistors? They are both the same except the TIP120 has a very high breakdown voltage and the more expensive (costs one penny more) TIP122 has an extremely high breakdown voltage. But the voltage in this project is only 12V so...
  10. audioguru2

    0-30 VDC Stabilized Power Supply 0.002-3 A

    I did not look into the transient that might occur when the power is turned on or off. Q1 was originally placed to short the output of opamp U2 because the old TL081 original opamps had a problem called "Opamp Phase Inversion" when an input voltage became too close to the negative supply voltage...
  11. audioguru2

    Design analog wave generator

    A square or rectangular wave has a fundamental plus many harmonic frequencies. It is simple to change the phase of one frequency but difficult (a time delay is needed) for many frequencies. Maybe a microcontroller and somebody to program it can be used.
  12. audioguru2

    0-30 VDC Stabilized Power Supply 0.002-3 A

    Many parts are changed or added so a new pcb is needed. Here are the latest parts list and schematic for the improved version:
  13. audioguru2

    0-30 Vdc Stabilized Power Supply

    Many zener diode datasheets do not show their tempco. These ones do: 1) The 1N5230B is 4.7V and 1N5231B is 5.1V at 20mA but their current is too high for the opamp that doubles their voltage. 2) The BZX79C5V6RL is 5.6V at 5mA which is why I selected it.
  14. audioguru2

    0-30 VDC Stabilized Power Supply 0.002-3 A

    I have never seen this defective new copy of the original project before. It has all the errors of the original project and added some new errors. The parts numbering has been changed so it is difficult to say that a resistor is 1/4W but must be 1W and its value should be xxx. Many parts are...
  15. audioguru2

    0-30 VDC Stabilized Power Supply 0.002-3 A

    I do not like to look at a pcb that has nothing labelled.
  16. audioguru2

    0-30 VDC Stabilized Power Supply 0.002-3 A

    OZ6YM, Which version of this project did you make: 1) The original Greek kit with many overloaded parts and it cannot produce 30V at 3A? 2) The improved circuit in the forums? 3) The Chinese copy of the Greek kit?
  17. audioguru2

    0-30 VDC Stabilized Power Supply 0.002-3 A

    You got excellent voltage regulation.
  18. audioguru2

    how to construct a mod-60 stopwatch counter?

    Nobody uses old fashioned TTL logic ICs anymore. Can you buy them anywhere?
  19. audioguru2

    0-30 VDC Stabilized Power Supply 0.002-3 A

    The peak voltage from a 24VAC transformer is 34V. It charges the main filter capacitor to this peak voltage and heats the load, rectifiers, series pass transistors, driver transistors and current sensing resistor. Then this 300W transformer is at its max current when the DC output current is...
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