audioguru

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Everything posted by audioguru

  1. No. An old condenser mic uses 48V and needs a preamp with a very high input impedance. It does nothing in your circuit. A modern electret mic (look it up in Google) is a condenser mic with 48V stored permanently in its electret material and has a Jfet inside that has a very high input impedance. The datasheets of electret mics show that the Jfet current is about 0.5mA and needs 2V to 10V, so your circuit will not work since the current in the 47K resistor reduces the voltage and current much too low. For 2.5V across a 0.5mA electret mic and a 5V supply then the resistor must be only (5V - 2.5V)/0.5mA= 5k but the 5k resistor and any other load (your volume control) loads down the output level. I use a 10k resistor and an 8V supply. Then it feeds a preamp with a 100K input impedance.
  2. The datasheet of a CD4017B shows that its output current into a 2V LED when it has a 5V supply is only 3.5mA or less (looks dim). Your circuit is mixing an old TTL 555 with an output voltage fairly low with a Cmos 4017 that needs a fairly high clock input voltage. A bad mix. I used a 74HC4017 (high current Cmos) clocked with a Cmos 555 and it makes very bright LEDs and since they are both Cmos they work together reliably.
  3. audioguru

    0-30V Stabilized Power Supply

    Why do you show an LT1038? it is obsolete and is not made anymore. It is impossible for it to dissipate 32V x 10A= 320W. Its datasheet shows that with a huge heatsink with fan or with liquid nitrogen for cooling it can dissipate only 120W. Its control circuit gives 10A only when its input to output is a few volts and cuts the max current to 2.5A when the input to output is 30V.
  4. Why do you show text that talks about an NPN transistor but you show a schematic with a PNP transistor? The Circuitspedia PNP circuit is missing the important diode parallel with the relay coil. The diode is shown on their NPN circuit.
  5. audioguru

    0-30 Vdc Stabilized Power Supply

    Surface mount ICs on adapters? Solder that was dripped on from up high and heated with a blow torch? All I can say after seeing your project is "EEK!".
  6. 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.
  7. 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.
  8. 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.
  9. 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.
  10. 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.
  11. 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.
  12. audioguru

    0-30V Stabilized Power Supply

    Good luck trying to cool 114W so that the case is not too hot.
  13. 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.
  14. 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.
  15. 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.
  16. 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??
  17. 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 #?.
  18. 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.
  19. audioguru

    0-30 Vdc Stabilized Power Supply

    I use copper wire, not rice wire. They put rice in everything they make, especially batteries.
  20. 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.
  21. audioguru

    0-30 Vdc Stabilized Power Supply

    The Chinese meter is messing up the voltage and current of the power supply project. Try the power supply project without the Chinese meter. Measure the voltage across R7 then calculate the current in it. The voltage across R7 will never be more than 1.414V when the current in it is 3.0A or less. Here are my calculations for the current calibration trimpot RV3:
  22. audioguru

    0-30 Vdc Stabilized Power Supply

    Which schematic are you using? Years ago when I replaced the low voltage TL081 opamps with higher voltage MC34071 or TLE2141 I replaced the D7 zener diode with two diodes so that the negative supply is only -1.3V. The 0V reference (zero point) for making measurements has always been the negative wire of C1, the main filter capacitor.
  23. audioguru

    0-30 Vdc Stabilized Power Supply

    Hi Tintin, Now you say you measured 27VAC from your 24V transformer when its load current is low. Then it is cheap and has a high resistance so they made its voltage 27VAC instead of if it had low resistance and an output closer to 24VAC. Or maybe the voltage of your AC electricity is higher than normal. The peak of 27VAC is 27V x 1.414= 38.2V and the full wave rectifier drops it to about 36.8VDC, not 44VDC.
  24. audioguru

    0-30 Vdc Stabilized Power Supply

    This project will not produce 30.0VDC at 3.0A with a 24V transformer. It might produce 25VDC at 2A with a lot of unregulated ripple.The transformer must be 28VAC or 30VAC at 4.2A. A 24V transformer will produce about 25VDC when it has a small load current which has a peak of 25V x 1.414= +35.4V and the bridge rectifier reduces it to about +34.0V. Maybe your transformer is cheap and has a small maximum current so it is made to produce a much higher voltage when it has a small load current (your 2.2k resistors) then its voltage drops when it is loaded with your 1k resistor. Or maybe your meter is measuring the AC ripple that is caused by the value of the total capacitance of C1 is too small.
  25. audioguru

    0-30 Vdc Stabilized Power Supply

    A solderless breadboard has intermittent contacts that cannot handle the high currents of this project. The many rows of contacts and wires all over the place have capacitance between them that frequently causes a circuit like in this project to oscillate at a high frequency. In my career I made all my prototypes soldered together on stripboard where I planned the layout to be compact and the strips were cut to length so that each strip was used for many parts of the circuit. Some of the circuits were very complex but worked perfectly and looked good enough to be sold as the final professional product.