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  1. audioguru2

    OVER-/UNDER-VOLTAGE PROTECTION CIRCUIT ANALYSIS

    It depends on the input offset voltage of the comparator. An LM393 dual comparator has a typical input offset voltage of 1mV (5mV max) and a typical voltage gain of 200,000. Its output would try to be 200V! Its output would be saturated at the positive supply voltage or at ground. If you use a...
  2. audioguru2

    Question about equalizer

    I mentioned a "pure" sine-wave because distorted sine-waves from function generators have 0.5% to 5% of harmonic distortion. If the harmonics are at 5% then ithey will be amplified a lot by the high frequency filter. Calculate how much 100Hz signal is at the output of the high frequency filter...
  3. audioguru2

    Need Help Voltage Regulator 12 vDC using 7812

    You need a transformer to match your mains voltage with a 12VAC /1.5A output. Calculate the value for a fuse on its input. The transformer feeds a bridge rectifier and a filter capacitor. The 7812 needs an input and an output capacitor as shown on the datasheet for the 7812.
  4. audioguru2

    Question about equalizer

    I will assume that the 100Hz input is a pure sine-wave without any harmonics. The low frequency section has a gain of 0.1. The high frequency section has a gain of 10.1. So the high frequency section has 101 times more gain than the low frequency section. Calculate how much of the 100Hz signal...
  5. audioguru2

    0-30 Vdc Stabilized Power Supply

    It is a current regulator, not a limiter. U3 reduces the output voltage so that the voltage across R7 (caused by output current) equals the voltage set by the current-setting pot.
  6. audioguru2

    Link for FM radio station

    You won't be designing it if you just copy the schematic of somebody else. At 200MHz you would cause and receive interference from TV stations and legal communication services. It is against the law to cause interference. If they interfere with your radio then it is your problem because they...
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    R7 is the current-sense resistor. It feeds the inputs of U3 with the current-setting pot making an offset voltage. When the voltage across R7 causes U3 to become active then its output begins to be reduced which causes it to reduce the output voltage until the current is at the set amount. U3...
  8. audioguru2

    OVER-/UNDER-VOLTAGE PROTECTION CIRCUIT ANALYSIS

    Some electric motors draw more current when the supply voltage is low. Then if the voltage is too low the motor will burn out. Some electric motors have a very high current surge when they start running when loaded. If the voltage is too low then they might not start running and just sit there...
  9. audioguru2

    The caps surrounding the LM7812 regulator?

    The datasheet says the input capacitor must be used and when. It also says the output capacitor stops certain problems. They are small and inexpensive so why not use them? The datasheet says "The input voltage must remain typically 2.0V above the output voltage" but some ICs need 3.0V. At 1A...
  10. audioguru2

    white led

    Hi Jgeidl, In his country a wall-wart is too expensive, the mains has high voltage surges and the LEDs don't have a forward voltage rating. It will be a miracle if he can make something that works.
  11. audioguru2

    white led

    You shouldn't operate the LEDs at more than their max current of 30mA each. 500mA/20= 25mA. I don't know how high your mains voltage surges. I don't know why because mine never does. So I don't know what will prevent it.
  12. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Kcc, Welcome to our forum. ;D U3 operates as a linear amplifier and does not switch like a comparator. Set the current for 1.0A and the voltage to 25V or 30V. Put on a 20 ohm load then the output voltage drops to exactly 20V, not zero. Put on a 10 ohm load and the output voltage drops to...
  13. audioguru2

    white led

    Sure, why not. You could use twenty 12k resistors. They will EACH dissipate 8.6W so the total amount of heat from them is 171W! They need to be rated at 10W each. Smd resistors can't dissipate 10W each. A 6V/500mA transformer will be safe, hardly waste any power and would cost less.
  14. audioguru2

    white led

    20 ordinary LEDs won't make much light. Maybe just enough for a little sign. When you rectify and filter 230VAC then you have 324VDC. Your LEDs and current-limiting resistors need only 5V and a little more if you have a voltage regulator. The voltage difference is a huge waste of power that...
  15. audioguru2

    Speech Recorder

    The spec's say that the minimum speaker is 16 ohms. Your 8 ohm speaker draws twice as much current and maybe caused the output transistors to blow up in the IC. Maybe your electret mic is a different type or maybe it is connected backwards.
  16. audioguru2

    Hiss Sound

    Did you use shielded audio cable from the guitar to the preamp circuit and from the preamp to the amplifier? Is the preamp in a metal box that is connected to the signal ground? Is the amplifier connected to earth? Does the hiss sound change volume when the output volume control on the preamp...
  17. audioguru2

    white led

    Hi Pier, Your LEDs are very dangerous without a transformer. The single resistor to pass 500mA and drop 315V is 630 ohms at 158W. Two resistors in a voltage divider would use more current because the current to ground is wasted. Do it like this:
  18. audioguru2

    The caps surrounding the LM7812 regulator?

    Ringing is like a bell. It begins oscillating when the input voltage or output current changes then the amplitude gets less and less, then it is gone. Ringing is a sign of poor stability because it is almost oscillating. Oscillation is a continuous signal.
  19. audioguru2

    The caps surrounding the LM7812 regulator?

    The regulator oscillates if its input is a high impedance. If the main filter capacitor is far away then the wires to it have inductace which is a high impedance. The input capacitor directly at the regulator prevents oscillation. The output capacitor stops the output from ringing when the...
  20. audioguru2

    OVER-/UNDER-VOLTAGE PROTECTION CIRCUIT ANALYSIS

    You can see that the LM358 dual opamp has nearly the same circuit as the LM393 dual comparator and they have a huge difference in speed. Some older opamps are under compensated so that they must have a closed loop gain of 5 or more. Their smaller frequency compensation capacitor allows them to...
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