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Posts posted by audioguru

  1. The output current is not shutoff when the current exceeds the current setting. Instead the current is regulated to drop to and stay at the setting:

    1) Voltage is set to 20.0V and current is set to 1.0A. No load. The output of U3 goes as high as it can, D9 is reverse-biased and does nothing.

    2) Voltage is set to 20.0V and current is set to 1.0A. A load of 10 ohms is applied. The output voltage must drop to 10 ohms x 1A= 10V and the output of U3 drops to about +3.13V. The input of U2 is about +3.73V.

    3) Voltage is set to 20.0V and current is set to 1.0A. The output is shorted. The output voltage must be 0V and the current must be 1A. The output of U3 drops to about -0.04V and the input of U2 is about +0.56V. The output of U3 will never go below -0.04V which does not harm it since its negative supply is -1.3V.

    The gain of the voltage amplifier is 30V/11.2V= 2.68 and the output of U2 never goes below about +1.2V due to the driver and output transistors Vbe voltage drops. The non-inverting input of U2 is always at least +1.2V/2.68= +0.45V when the voltage and current settings are zero and there is no load. Many ordinary opamps have inputs that do not work when they are a few volts from the negative supply pin, but the inputs of the TLE2141 work all the way down to the negative supply pin voltage.


    Isn't the idling current simply the 3.4mA to 4.4mA current of U2? You are correct, U2 gets hot but not too hot. The driver and output transistors need huge non-enclosed heatsinks or a fan.    

  2. Can the wind from a fan push a wing that pushes on a changeover switch? Then when the fan is slow or it stops (even if its electrical power gets cutoff) the changeover switch changes the light from green to red. The switches must use diodes and resistors and DC to make an "OR gate". The DC from the OR gate can activate triacs that turn on and off the lights. 

  3. I hate it when people copy a schematic and change all the parts numbers around.

    The original schematic has U3 as the current regulator, U1 as the voltage reference and U2 as the voltage regulator. I kept them on all my updates.

    Rev7 was drawn by Liquibyte and has U1 as the current regulator, U2 as the voltage reference and U3 as the voltage regulator which is VERY confusing.

    Even his resistors, capacitors and transistors have different numbers.

    Instead of you changing the wiring and causing idle current errors and maybe even having hum on the negative supply affecting your voltage readings simply use the circuit's 0V as the meters ground and measure the voltage across the current-setting pot for the current limit setting and measure the voltage across the current sensing resistor as the actual current of the load.    

  4. Why don't you look at the datasheet that shows both darlington transistors?

    They are both the same except the TIP120 has a very high breakdown voltage and the more expensive (costs one penny more) TIP122 has an extremely high breakdown voltage. But the voltage in this project is only 12V so either Mosfet  darlington will be fine.


    We do not know how much current your motor uses so it might overload the darlington transistor. 

  5. I did not look into the transient that might occur when the power is turned on or off. Q1 was originally placed to short the output of opamp U2 because the old TL081 original opamps had a problem called "Opamp Phase Inversion" when an input voltage became too close to the negative supply voltage when the negative supply collapsed first when the power was turned off. It would have caused the output of the opamp U2 to suddenly go as high as it can which is bad for the speaker. The new opamps do not have this problem.

    You can add Q1 and its resistors if you want.

  6. I am talking about this project http://www.electronics-lab.com/project/0-30v-laboratory-power-supply/
    at the PCB...
    The return-line for MINUS or the GROUND-WIRE is to thin...
    Make it bigger to take 3 Amp at 30 Volt.

    That is my comment....
    ...what a guru...

    I have never seen this defective new copy of the original project before. It has all the errors of the original project and added some new errors. The parts numbering has been changed so it is difficult to say that a resistor is 1/4W but must be 1W and its value should be xxx. Many parts are overloaded and the opamps have a total supply voltage too high for them.

  7. The peak voltage from a 24VAC transformer is 34V. It charges the main filter capacitor to this peak voltage and heats the load, rectifiers, series pass transistors, driver transistors and current sensing resistor. Then this 300W transformer is at its max current when the DC output current is 8.8A.


    The inputs of some 741 opamps fail to work when their voltage is within 4V from the positive or negative supply so the 1.3V from the two diodes is not enough. Use the negative -5.6V supply in the original circuit.

    The LM311 is a comparator, not an opamp. It its voltage gain is 200,000 times and it oscillates if it has negative feedback.


    Maybe you calculated with "typical" current gain. Then you must buy a few hundred transistors, test their gain and use only the best ones. We usually design circuits so that all of them work well even if the transistors have minimum specs.


    We do not use "China" transistors or ICs. Instead we use Name Brand genuine parts.

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