audioguru

Members
  • Content count

    11,961
  • Joined

  • Last visited

  • Days Won

    1

audioguru last won the day on March 5

audioguru had the most liked content!

About audioguru

  • Rank
    Advanced Member

Profile Information

  • Gender
    Male

Recent Profile Visitors

The recent visitors block is disabled and is not being shown to other users.

  1. audioguru

    0-30 Vdc Stabilized Power Supply

    No and No. U1 has a gain of 2 times and a 5.6V Zener diode. Therefore its output is 11.2V, not 33V. A 5.6V Zener diode does not change its voltage when its temperature changes but an 11.2V Zener diode increases its voltage if it gets warmer. The BD139 and the output transistors are emitter-followers. Their emitter voltage follows their base voltage but at high current, their base voltage is 1V to 1.5V higher than their emitter voltage. Then when the output voltage is 30V the output of U2 must be 32V to 32.5V.
  2. audioguru

    0-30 Vdc Stabilized Power Supply

    My Rev 6 July, 2014 schematic shows that opamp U1 makes the 11.2V reference, U2 is for the voltage control and drives the output driver transistor with 0V to about +32V and U3 is for the current control and has an output from -1.0V to about +27V. If the output has a low voltage (or is shorted) and a high current then the NPN output transistor in U2 will get hot. A tiny little surface mount package cannot dissipate much heat.
  3. audioguru

    0-30 Vdc Stabilized Power Supply

    I did not calculate it but I think a tiny surface mounted opamp for position U2 will get too hot if the hFE of the driver and/or output transistors is low.
  4. audioguru

    Changing just the AC Frequency

    If you make a circuit that uses high frequency pulse-width-modulation for making the 60Hz sinewave then its could be 90% efficient and produce "only" 120W of heat when its output is 1200W. Then it would need a pretty big heatsink with cooling fins.
  5. audioguru

    Changing just the AC Frequency

    Use the 120VAC 50Hz to drive a 110V 60Hz motor driving an alternator. Use magic to adjust the frequency Make an audio amplifier powered from 120VAC 50Hz with 120VAC 10A (1200W!) output and feed it a 60Hz sinewave.
  6. audioguru

    0-30V Stabilized Power Supply

    Maybe you use the power supply to test a 3A forward biased diode. Then the output transistor gets very hot.
  7. audioguru

    0-30V Stabilized Power Supply

    Good luck trying to cool 114W so that the case is not too hot.
  8. audioguru

    0-30V Stabilized Power Supply

    I wrongly typed 114A instead of 114W. A single 2N3055 will be at its maximum allowed chip temperature of 200 degrees C when it dissipates 115W and its case is cooled to no more than 25 degrees C with liquid nitrogen or something. A heatsink also gets hot even when it is huge and has a fan blowing on it. I never operate a transistor anywhere near its maximum temperature, voltage or current. Then it is reliable.
  9. audioguru

    0-30V Stabilized Power Supply

    Your idea to use only one 2N3055 output transistor will have it burning hot (38V x 3A= 114A!) if the current is set to 3A and the output is shorted or has a very low voltage. Two output transistors share the heat. Their emitter resistors match them pretty well. Two output transistors at b1.5A each will have a higher hFE than only one transistor at 3A then the driver transistor does not need to supply a higher current and it also stays cooler.
  10. audioguru

    0-30 Vdc Stabilized Power Supply

    The peak of 30.5VAC is 30.5V x 1.414= 43.13V. The bridge rectifier has diode voltage drops of 1.4V when there is no load so the positive supply will be 43.13V - 1.4V= 41.73V. If your mains electricity voltage rises then the opamps might be destroyed. I do not know why your voltage measurements are wrong. A 28VAC transformer is about 29VAC with no load. Then its peak is 41.0V and the bridge rectifier reduces it to 39.6V with no load which is fine for the 44V opamps.
  11. audioguru

    0-30V 3A - I need some answers

    15A output current is much too high for this circuit designed for a maximum of 3A using two output transistors to share the heat. Your schematic shows only one 2N3055 output transistor so its maximum output current will be only 1.5A. There are three MC34071 ICs. Which one do you have a problem? You said, "I did not get the circuit". It is not English, what do you mean to say??
  12. audioguru

    0-30 Vdc Stabilized Power Supply

    When you turn down P2 to zero then the project's output current should be no more than a few mA. The circuit reduces the output voltage with U3 and D9 to reduce the current. When the current is limited to a few mA then the anode of D9 is 0V and its cathode which is driven from the output of U3 must be about -0.65V. That is why U3 is an opamp that has its input and output able to go close to its negative supply and why it has a negative supply. When you turn up P2 then the current does not go up, the voltage and the load resistance set the current. The maximum current goes up. The circuit is designed for a maximum current of 3A so you should set the current calibration trimpot RV3 so that with P2 at maximum and with the output of the project shorted then the current is 3.0A. If RV3 is set to its maximum of 100k then the maximum output current will be 1.33A as I showed in post #?.
  13. audioguru

    0-30 Vdc Stabilized Power Supply

    165mV/500mA= 0.33 ohms that is wrong. 215mV/1A= 0.215 ohms that is also wrong. 1.304V/3A= 0.435 ohms which is close to your measurement of R7. Then trimpot RV3 is set for a max current of 3A or less. When the output current is higher than the setting of P2 then the output of U3 goes low which turns on the LED and reduces the voltage at the output amplifier. Then the shorted output should have a current of 3.0A maximum. The opamp used for U3 and the negative supply voltage must be allow the output of U3 to go low enough so that the input to the output amplifier is shorted to 0V when the output of the project is shorted. Then R7 is the load.
  14. audioguru

    0-30 Vdc Stabilized Power Supply

    I use copper wire, not rice wire. They put rice in everything they make, especially batteries.
  15. audioguru

    0-30 Vdc Stabilized Power Supply

    5V on 10 ohms produces a current of 500mA (0.5A). Then the voltage across R7 is 0.235V. On your schematic, C is the ground for the current regulator. The output ground is its input signal and the 11.2V is its reference voltage.