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Everything posted by audioguru

  1. 0-30 Vdc Stabilized Power Supply

    The Chinese power supply uses relays to switch the transformer voltage into voltage ranges so that the output transistor does not get too hot. I do not know if any parts are overloaded and I do not know how good or bad is its regulation. Its LM741 opamps were designed 50 years ago (!).
  2. 0-30 Vdc Stabilized Power Supply

    Your photo of a no-name-brand Chinese power supply does not show any specifications and does not show its schematic and parts list. The photo shows its 30VDC output when its current is zero. The defective Greek kit and Chinese copies do that but cannot produce 30VDC at 3A. Instead they produce about 25VDC with a lot of ripple at 2.5A and the parts are burning.
  3. 0-30 Vdc Stabilized Power Supply

    This project has been copied and is available for a very low price on ebay, Banggood and Amazon. But it has all the problems of the original kit from Greece. Many parts are overloaded and fail soon. It does not produce 30VDC at 3A. It looks like the Chinese people who copied it never made it and never tested it.
  4. 0-30 Vdc Stabilized Power Supply

    The original project had many overloaded parts including the power transformer. It used TL081 opamps but your TL071 opamps are simply TL081 opamps selected fo low noise (audio applications). Their absolute maximum supply volyage is 36V but this project with a 24VAC transformer produces about 25VAC when the load current is low then its peak is 35.4V which is reduced to about +34V which is the positive voltage for some of the opamps and -5.6V is the negative supply for them. Then they get 34V plus 5.6V= 39.6V which is too high for these opamps so they will fail soon. The improved modified circuit uses opamps rated at 44V and the -5.6V supply is reduced to -1.3V. Of course the output transistor gets hot when loaded, even with a huge heatsink because it and the driver transistor are overloaded. The improved modified circuit uses a better driver transistor with a proper case that can be bolted to a larger heatsink and TWO output transistors are used to share the heat. Use a fan if you want. It is easy to find a table of wire size and the current it can handle, and use Ohm's law to calculate its voltage drop. Use #18 AWG wire and solid core or stranded are both able to carry many amps of current with a low amount of voltage drop. The overloaded transformer is rated at 24V x 3A= 72VA but needs a transformer that is 28V x 1.414 x 3A= 119VA instead then its voltage will not collapse when loaded. But then the 44V opamps must be used. It should be obvious to you that when the current setting is set low (you cannot turn it off) then any load current higher than the setting will reduce the output voltage. It should have excellent voltage regulation. If the current setting is 2A and you load the project with 1.5A then the output voltage might be 25.0V with the load and the voltage set to 25.0V and when the load is disconnected the voltage might rise to 25.005V, or be 25.0V with 2A and drop to 24.095V without a load.
  5. 0-30V 0-3A Latest Data Discussion

    No, it is a power supply, not a charger.
  6. 0-30 Vdc Stabilized Power Supply

    No, it is a power supply not a charger. Then this modified power supply project will have a maximum regulated output of only about +25V at 3A.
  7. 0-30 Vdc Stabilized Power Supply

    Since it was years ago I do not remember which page of which thread has version 6 or 7. I have the schematic and parts list of version 6 here:
  8. Build A Wooden Portable Speaker Box

    The speaker drivers look tiny, 2 inches or 3 inches in diameter like a cheap clock radio? No bass. The PAM8403 amplifier IC produces 3 Whats with high distortion into a 4 ohm speaker per channel or 2 Watts at less but still audible distortion when the supply is 5V. Have you heard the Bose little Bluetooth mono speaker? It sounds great and costs $200.00. Why is your speaker stereo? The speakers are too close together for stereo. If you made a mono speaker with the same size enclosure then the speaker driver can be larger for better bass.
  9. Circuit Diagram of D313 Power Amplifier

    This thread is 13 years old! The maximum allowed supply for a 2SD313 is 60V so the +35V/-35V is too much. If it has a huge heatsink then it can heat with 30W and have an output of 25W x 4= 100W from an amplifier. If its output swing is 50V p-p which is 17.7V RMS then the power in an 8 ohm speaker is 39W or about 70W into 4 ohms. If two if these amplifiers are bridged then the power in an 8 ohm speaker is about 137W. Peak or very distorted power is double.
  10. High volt power supply

    Why? If the device needs a high voltage but you give it a low voltage then it probably will not work (not do anything).
  11. N-Channel Mosfet switch

    The threshold voltage Vgs of a Mosfet is when it is barely turned on and is almost turned off. It is not 2.8V, it is somewhere between 2.2V and 3.4V. You need a Vgs to fully turn it on which is shown as between 6v and 10V on the datasheet. I can't remember why you want the Mosfet to short the three 680uF output capacitors. I do not know why the input (-) is not the circuit ground.
  12. 0-30V Stabilized Power Supply

    The TLE2141 opamp has PNP input transistors so that the outputs work with an input as low as 0V. Then you must pull the input down and not let it float up. Your multimeter pulls the input of the opamp down. The maximum input bias current for a TLE2141 opamp is 2.1uA that tries to pull the input voltage up.
  13. 0-30V Stabilized Power Supply

    The middle opamp in Liquibyte's schematic is the 11.2V reference because it uses a 5.6V zener diode and it has a gain of 2 times. The voltage setting pot R27 is simply a voltage divider that feeds 0V to 11.2V to the non-inverting input pin 3 on the opamp on the right side. The gain of this opamp is 1+ (56k/28.8k)= 2.9444 times so that the maximum output of the circuit is 11.2v x 2.9444= 30.0V. Your middle opamp is messed up since its output voltage is too low.
  14. 0-30V 0-3A Latest Data Discussion

    I cannot remember my fix for the "on" voltage spike. If you remove the negative supply then you will not be able to limit shorted output current less than about 0.43A since the transistor that replaces the diode cannot go lower than its max saturated output of about 0.2V. 0.2V/0.47 ohms= 0.43A.
  15. 0-30V Stabilized Power Supply

    Nand, Simply calculate the amplitude of the 120Hz (or 100Hz) ripple that will be produce when the load draws 3A. It won't be regulated with that much ripple.
  16. 0-30 Vdc Stabilized Power Supply

    You must change the values of the parts that try to produce volts and amps outputs higher than you will get. You can calculate the maximum regulated output voltage, maximum regulated current and maximum heat produced by the transformer then try adjusting the calibration pots to see if they will limit V, A and P low enough. 24VAC has a peak of 34VDC. Your 24V/3.33A transformer is overloaded with more than 80VA. The maximum output of the circuit will be about 25VDC at about 2.3A
  17. 0-30V Stabilized Power Supply

    Audio amplifiers do not need a voltage regulator or a current regulator. A car radio amplifier is powered directly from the car battery with no voltage regulator but the low current radio parts might use a simple little voltage regulator. 14V at 6A is 84W! One amplifier produces a maximum output of 16W into a 4 ohm speaker then 4 channels make 64W. If all 4 amplifiers are producing 64W then if they are linear they heat with an additional 36W and the current is 7.14W but it does not need to be regulated.
  18. 0-30 Vdc Stabilized Power Supply

    The original Greek kit and the first Chinese copy wrongly said to use a 24V/3A transformer that does not work and becomes overloaded. Its voltage is too low for the project to produce 30VDC at 3A and its voltage is too high for the opamps with a low maximum supply voltage rating of only 36V. The original opamps also needed an additional negative supply with a fairly high voltage. We corrected the circuit and used opamps with a 44V maximum supply voltage rating and a 28V/4.24A transformer (the peak of 28VAC is 39.6V). With an output current from the project of 3A then the transformer must supply 39.6V x 3A= 188.8VA. Then the current rating of the transformer must be 118.8VA/28VAC= 4.24A. The improved circuit also works with a 30AC transformer and you can calculate its current rating needed. The current limiting is variable from about 2mA to 3A and has excellent current regulation. If the output is shorted then the current will not cutoff, instead it will be at the current setting. Many stores do not provide datasheets that are available online from the manufacturers. Wakefield is a heatsink manufacturer and has datasheets of all their heatsinks at their online site.
  19. 0-30 Vdc Stabilized Power Supply

    If you use a 24V/4A transformer then its maximum allowed output is 24 x 4= 96VA. Then the project maximum output current must be calculated with the 34V peak voltage (96VA/34VDC= 2.8A). You can simply calculate how much heating (volts times Amps) a 2N3055 will survive by its thermal spec's and the heatsink thermal specs on their datasheets.
  20. 0-30 Vdc Stabilized Power Supply

    If you use fine and coarse controls then one will always be in the wrong position. Use larger knobs instead. Higher output current will cause a heat problem in the output and driver transistors. The improved version of this project already uses two output transistors to share the heat produced at 3A. Use a huge heatsink and a fan for 4A output. Change R7 to be 0.35 ohms/10W. A 24VAC transformer is too low for this project to produce 30VDC output at 3A or 4A but the original TL081 opamps will have a voltage too high for them if the transformer voltage is increased. The improved version of this project uses TLE2141 opamps rated at a supply of 44V and a 28VAC or 30VAC transformer. A transformer rated at 24V/4A has a limit of 24V x 3A= 72VA. But here the 24V is rectified to produce a peak voltage of 34V. Then if the load on this project is 3A the transformer produces 34V x 3A= 102VA. It must be rated for 102VA/24V= 4.25A. If the output of this project is 4A then the transformer must be rated for 5.7A.
  21. Power supply

    AC might be Air Conditioner? The power required depends on its efficiency. A high efficiency AC uses much less power than an old low efficiency one.
  22. Using 1N4148 As A Temperature Sensor

    A zener diode is used with reverse bias voltage. A temperature sensing diode is used with forward voltage that is completely different. Look at the datasheet of a 1N4148 diode. Its forward voltage is shown at -40 degrees C, at +25 degrees C and at +65 degrees C. The forward voltage drops as the temperature of it rises. Test it at a current of 0.1mA to 10mA at different temperatures.
  23. DIY a Compact RC Switch

    The circuit will never have a negative voltage in it. P1 will smoothly give 0V to +5V to pin 2 as it is rotated. The input current of pin 2 is so low that a 10k or 20k pot will make no difference. R4 limits the T1 base current to only 0.3mA then tie relay might not be activated if it needs 6mA or more. The current in R4 must be at least 1/20th the current in the relay coil. The BC547 works poorly at currents above 50mA.

    You mentioned relays. Then you do not want speed control? Jerky on-off is called "bang-bang control" in cheap kids toys. What will happen to the motor when it is running forward at full power then you suddenly change it to run in reverse at full power? The fuse will probably blow to save the motor. You need a circuit to delay switching directions.
  25. You forgot to attach the schematic of your circuit for us to see anything wrong.