Search results

  1. audioguru2

    Problem with output voltage of simple PWM DC motor speed controller

    PWM are pulses that many DMMs cannot measure properly. An analog voltmeter will correctly show the average voltage. The speed control circuit is simple and has no RPM feedback so the speed of the motor will change a little when its load changes.
  2. audioguru2

    0-30 Vdc Stabilized Power Supply

    A 5.6V zener diode (a low current 5mA one should be used) was selected because a 5.6V to 6.8V zener diode has a stable voltage when the temperature changes. A lower voltage zener diode has a voltage decrease as the temperature rises and a higher voltage one has a voltage increase when the...
  3. audioguru2

    0-30 Vdc Stabilized Power Supply

    Redwire recommends using a voltage regulator IC instead of this pile of parts that use a zener plus an opamp. We are using modern TLE2141 opamps that also have a max supply of 44V and inputs that work all the way down to the negative supply so we do not need a negative supply for opamp U2 (but...
  4. audioguru2

    0-30 Vdc Stabilized Power Supply

    That is another problem with the original circuit. I agree that Q1 should short the base of Q2 to ground (not the output of U2) when the power is turned off. The TL081 opamp has the problem called "Opamp Phase Inversion" where the output suddenly goes high when an input voltage gets too close...
  5. audioguru2

    0-30V stabilized power supply: construction problem.

    Please post the answers to these DC voltage measurements: 1) What is the voltage at the output of U1? It should always be about +11.2V. 2) When the voltage pot P1 is turned from zero to maximum what is the voltage at the input pin3 of U2? It should change from 0V to about +11.2V. 3) When the...
  6. audioguru2

    MOSFET replacement

    The original 20N60S5 has a much lower max on-resistance than the W20NM60 so if the current is high then the W20NM60 will get too hot because it will waste more voltage.
  7. audioguru2

    0-30V stabilized power supply: construction problem.

    I think your driver or output transistor is shorted or has its pins connected wrong. U2 will get hot quickly when it tries to hold its output voltage down but is connected to a short to the positive 32V. R15 will also get very hot.
  8. audioguru2

    0-30V stabilized power supply: construction problem.

    Did you build the original circuit without changing anything? You need to troubleshoot the circuit to see what is wrong. 1) We need to know how close the output voltage is to the unregulated voltage across C1 because the output voltage from opamp U2 cannot go higher than about 1V less than the...
  9. audioguru2

    0-30V stabilized power supply: construction problem.

    Are you learning how to copy a circuit and learning how to solder its parts together? If you learned the details of electronics and designed the project yourself then it would probably work perfectly and be very reliable. Since you simply copied it then show its problems and how you will fix...
  10. audioguru2

    0-30V stabilized power supply: construction problem.

    1) The 24V transformer produces a peak voltage of 33.9V at its rated power. The main filter capacitor charges to the peak voltage minus 2V. When the project has an output current of 3A then the transformer must produce 33.9V x 3A= 101.7VA. But it is rated at only 24V x 3A= 72VA so it is...
  11. audioguru2

    amplifier types

    Biasing has nothing to do with input resistance or output resistance. Biasing allows a transistor to be a linear amplifier. If it is biased wrong then it rectifies the signal with horrible distortion because it is very non-linear. A common emitter transistor has a much higher input resistance...
  12. audioguru2

    amplifier types

    No. A single transistor is not an audio power amplifier. Simple arithmetic shows why. The output voltage from a microphone is about 0.01V. 2W into an 8 ohm speaker is 4V RMS. Then a voltage gain of 4V/0.01V= 400 is needed. The output current from a microphone is about 3.7uA. 2W into an 8 ohm...
  13. audioguru2

    0-30V stabilized power supply: construction problem.

    The original project is missing calibration trimpots. If a 5% zener diode and 5% resistors are used then the maximum voltage can be plus or minus 25%. If the zener diode and resistors are very accurate: 1) Change R11 to 47k, then the maximum voltage output will be +24.5V. 2) Change R18 to 150k...
  14. audioguru2

    amplifier types

    No. A voltage amplifier does not "need" a high input resistance: 1) A common-base transistor amplifies voltage but has a low input resistance. A common-emitter transistor also amplifies voltage but has a fairly high input resistance. 2) An inverting opamp amplifies voltage and can have a very...
  15. audioguru2

    amplifier types

    You can use an opamp that is a very good voltage amplifier. But it has low output current. You can use an emitter-follower transistor that is a good current amplifier. But it has no voltage gain. Power is voltage times current. A power amplifier can have good voltage gain and good current...
  16. audioguru2

    0-30V stabilized power supply: construction problem.

    The transformer should be 20VAC at 42VA. The gains of the voltage and current amplifiers must be reduced. Then it will produce 0-20V at up to 1.5A very well.
  17. audioguru2

    0-30V stabilized power supply: construction problem.

    I did not save a pcb design but there are some pcb designs for the new version of this project in the forums.
  18. audioguru2

    0-30V stabilized power supply: construction problem.

    If you made the original project then many of its parts are overloaded. Some of the overloaded parts will fail so the project is not reliable. The original project will not produce 30VDC at 3A, it might produce 30VDC at 100mA and 25VDC at 3A. The forum describes a modified circuit that has...
  19. audioguru2

    Variable Power Supply With LM7812

    This new project is here: http://www.electronics-lab.com/projects/power/026/index.html It has some serious errors: 1) It says and shows LM7812 but it links to the datasheet of an L7812 that is different. 2) It does not say its adjustment range of output voltage. 3) The datasheets of the L7812...
  20. audioguru2

    0-30V Stabilized Power Supply

    My fourth comment is about the clarity of your schematic. The large one is much too large for my pc screen and clearly shows only a small part of it. The small one is a perfect size but its fuzzy faint lines and text are difficult to see. My schematic is also shown here.
Top