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  1. audioguru2

    Car stereo amplifier

    It is obsolete. If it fails then you might not be able to replace it. Why didn't you look at its datasheet to see that it is designed to use a 24V supply that is not available in a car? Its datasheet shows that its output per channel is only 3.5W into 4 ohms with fairly high distortion with a...
  2. audioguru2

    Car stereo amplifier

    The TDA1554 amplifier IC is obsolete and is not made anymore. The two largest American parts distributors (Digikey and Newark) do not have any. It was not very good anyway. Its output was 22W per stereo channel into 4 ohms when its supply was an over-charging 14.4V battery and its distortion...
  3. audioguru2

    0-30V Stabilized Power Supply

    Kevin, the improved and fixed project uses opamps with PNP bipolar transistor inputs, not Jfet inputs so that they work with an input voltage as low as the negative supply voltage. The input voltage of opamp U2 goes from 0V (its negative supply voltage) to +11.2V and never goes as high as the...
  4. audioguru2

    0-30V Stabilized Power Supply

    Sorry, It is R17 that should be increased a little. Here I show that when R17 is the original value of 33 ohms, the TLE2141 opamp U1 has its maximum supply current of 4.4mA, its load is 5.6mA and its input offset voltage is at its maximum of 1.4mV. Then the output of U3 is low and turns on the...
  5. audioguru2

    0-30V Stabilized Power Supply

    The LED lights to warn you that the current regulation is reducing the output voltage because it senses that the load current is higher than a few mA set by the value (33 ohms) of R21. I notice now that the idle current and load of U1 is part of the load and the idle current of the TLE2141 is...
  6. audioguru2

    0-30V Stabilized Power Supply

    With the voltage control P1 set to zero then adjusting RV1 should change the output voltage of the project from about -30mV to +30mV. Then it can be set to 0.0V.
  7. audioguru2

    0-30V Stabilized Power Supply

    The modified parts list shows that a 5k trimpot if the opamp U2 is a TLE2141 and should be a 10k trimpot if the opamp U2 is an MC34071. Also, R10 should be 1k if the opamp is a TLE2141 and R10 should be a piece of wire for an MC34071. RV1 should be adjusted so that the output with or without a...
  8. audioguru2

    0-30V Stabilized Power Supply

    If you use 56k for R18 or 33k with a 100k series calibration trimpot set to about 23k, your P2 is 10k and R17 is 33 ohms then pin 3 of U3 should be about +5.6mV when P2 is at minimum. The LED will be off if your opamp has normal very low input current and low input offset voltage. But I do not...
  9. audioguru2

    0-30V Stabilized Power Supply

    This power supply should not have two or more connected in parallel because the voltage and current regulators will fight each other. It will be very difficult to set the output voltages exactly the same anyway. The current regulator reduces the output voltage when the output current exceeds...
  10. audioguru2

    Current limited Power Supply

    Please post the schematic you used, not a link to a page full of circuits.
  11. audioguru2

    0-30V Stabilized Power Supply

    An ammeter has a resistance that spoils the excellent voltage regulation of this project because its resistance is in series with the load. Instead, measure the voltage aross R7 then calibrate it in Amps. R7 is inside the negative feedback loop so it does not affect the output voltage.
  12. audioguru2

    0-30 Vdc Stabilized Power Supply

    You did not look at the specs for your opamps and transistors like I did so only SOME of your circuits will work properly. I designed my circuit so that ALL circuits will work properly. I always use WORST CASE SPECS in my designs so that all my circuits work properly. I have designed and had...
  13. audioguru2

    0-30 Vdc Stabilized Power Supply

    I simply stated the problems with your re-design. But then the opamps will probably over-heat. Single opamps should be used. Also, the negative supply of only 3.0V is too low for a TL082 that has an input common-mode range of 4V from the negative supply voltage. When the output is shorted or is...
  14. audioguru2

    7912 as negative voltage regulator issue

    Hee, hee. I did not notice that the supply polarity was backwards.
  15. audioguru2

    0-30 Vdc Stabilized Power Supply

    Your circuit has problems: 1) Its supply to IC1B is only 33V so the maximum output voltage at 3A is about 25V with lots of ripple, not regulated properly at 30V. The opamp has loss, R14 has loss, the driver transistor has loss and the output transistor has loss. The losses add to almost 10V. 2)...
  16. audioguru2

    7912 as negative voltage regulator issue

    Why didn't you look at the datasheet for the 7912?? It shows an input capacitor and an output capacitor that prevent it from oscillating at a high frequency which causes heating. The voltage from its input to output TIMES its load current sets how much dissipation (heating) it makes when the...
  17. audioguru2

    0-30 Vdc Stabilized Power Supply

    Opamp U1 has a voltage gain of 2.0 and uses a 5.6V zener diode so its output is always +11.2V. Voltage pot P1 feeds from zero to +11.2V to opamp U2. Opamp U2 and the driver and output transistors are a power amplifier with a voltage gain of 30.0/11.20V= 2.68 times. Opamp U3 compares the output...
  18. audioguru2

    0-30V Stabilized Power Supply

    Maybe Kevin needs to be de-fragged or re-formatted.
  19. audioguru2

    ohms law help

    50k is not a standard value. Use two 100k resistors in parallel. Would it be fair and correct to use a low value (something) for “I” ergo R=V/I  and solve for R9  R=2.5/.00001 = 250,000 ohm?
  20. audioguru2

    ohms law help

    It is simple. You want R9 to have 2.5V across it and want R10 to have 0.5V across it. The opamp is Cmos with zero input current so high value resistors can be used if you want. R9 must have a value that is (2.5/0.5=) 5 times higher than R10. A problem is that R10 is a variable resistor that will...
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