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audioguru last won the day on January 11

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  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. 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.
  9. You forgot to attach the schematic of your circuit for us to see anything wrong.
  10. 0-30V PSU - prblem with current limiter

    A 24V transformer has a voltage too high for the TL081 opamps. Use a transformer with a lower voltage like 15V. Replace the opamps that were strained. Replace the old fashioned 2N2219 with a modern BD139 transistor on a real heatsink. Replace the single 2N3055 output transistor that might be shorted. Re-calculate the values for the resistors that set the voltage and current.
  11. 0-30V PSU - prblem with current limiter

    The original project has many parts that are overloaded and they fail soon. We modified it to make it work better and to be more reliable.
  12. Sports Training Timer

    We will help you if you build or design a circuit that does not work properly. But it sounds like you want somebody to design a circuit for you. Somebody might do it.
  13. 0-30 Vdc Stabilized Power Supply

    We talked about fixing the cheap Chinese Banggood kit on another website and I do not want to talk about it again.
  14. 0-30 Vdc Stabilized Power Supply

    I think the kit from Banggood and copies of it are selling at a clearance price today because it has been replaced with a better kit maybe with its errors corrected. Of course the new kit costs much more and comes with voltage and current displays.
  15. 0-30 Vdc Stabilized Power Supply

    The original circuit has many overloaded parts and cannot produce 30VDC at 3A. It is also missing the calibration trimpots that are used in the improved version that can be set to exact maximums of 30.0V and 3.0A.