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  1. audioguru2

    Switching idea

    An inverting opamp can have a negative input voltage on its input resistor, and the negative feedback through its feedback resistor causes its output to be positive. The circuit can't have much gain to avoid having the opamp's input from becoming negative.
  2. audioguru2

    signal waveform generator

    Sorry, it is (was) XR2206 but I don't think it is made anymore. Its datasheet is here: http://www.datasheetarchive.com/semiconductors/download.php?Datasheet=2327414
  3. audioguru2

    Switching idea

    It's a can of worms! I didn't notice the negative input voltage that is bad for the comparator. You could level-shift it up to a positive voltage with a voltage divider or inverting opamp circuit.
  4. audioguru2

    LED amperage question

    If you shine a very bright light or same kind of LED on an LED it will generate only a couple of uA when used as a solar cell, because its chip is so small.
  5. audioguru2

    need help...how to use ne5534?

    The original circuit with a single NE5532 dual opamp didn't have compensation and balance pins so when using two NE5534 single opamps to replace it then don't connect anything to those pins. The compensation pins are for a capacitor to be added to reduce the opamp's high frequency response to...
  6. audioguru2

    Switching idea

    Correct. A standard comparator has just the collector of an NPN transistor at its output. An opamp has a complimentary NPN-PNP set of emitter-followers with their emitters (and maybe a series resistor of about 75 ohms) at their output.
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Tim, It's great to hear that you've fixed it. ;D Connect your voltmeter directly to the output terminals because the internal wiring has some voltage loss. A current meter in series with the load has a resistance that ruins the fabulous voltage regulation of this project. Instead, I would...
  8. audioguru2

    signal waveform generator

    I guess you don't want to use a precision but simple ICL8038,  XR20x6 or MAX038 waveform generator IC like I used about 25 years ago. In Google, lookup Wien Bridge Oscillator circuit and you will find many circuits like the generator I built last year and similar to my very 1st project that I...
  9. audioguru2

    0-30 Vdc Stabilized Power Supply

    The output of U3 is miles away from any transistors. I think its output is shorted to the positive supply. Pin 6 is close to pin7.
  10. audioguru2

    Switching idea

    Your new circuit depends a lot on a low voltage across the LED (less than about 2V). It would be better if you used an opamp for the Schmitt trigger and have the CTRL input of the CD4066 driven very high and low by its output. Then you can use a little 8-pins LM393 dual comparator instead of the...
  11. audioguru2

    Input signal for LM3915. need help.

    If you use positive and negative supplies for the half wave detector, you can use any opamp but the circuit will need the 2nd diode you had. A resistor from the half wave detector opamp's + input pin to ground will reduce input offset voltage but not eliminate it enough for two LM3915's that...
  12. audioguru2

    need help...how to use ne5534?

    Hi Zefiris, Welcome to our forum. ;D The NE5532 is a dual opamp. It has two opamps inside. The NE5534 is a single opamp so you will need two of them to replace an NE5532.
  13. audioguru2

    Input signal for LM3915. need help.

    I recommend using the TL071 as a microphone preamp because it is low noise, low distortion and wideband at high gain. Since it is so popular in audio equipment it is inexpensive. ;D
  14. audioguru2

    Switching idea

    If you want a transmission gate then use a transmission gate. A Cmos CD4066 quad transmission gate IC works well with a 12-13V supply and is about 100 ohms when on and infinite when off. 4 of them in the package can be paralleled for 25 ohms on resistance. The positive supply or a little less...
  15. audioguru2

    Switching idea

    You are in NZ? Isn't everything upside-down there? ;D When the PNP is supposed to be off, when the PWM's voltage exceeds the divider's 5V by 0.6V then it turns on. When the PNP is supposed to be on, the LM339 feeds it a weak base current so it will be a resistance that might slow-down the rise...
  16. audioguru2

    500W_inveter

    Hi Ren, Welcome to our forum. ;D Ronnie drew the schematic and built the 1st fixed and improved 500W inverter. He is in the Philippines so e-mail him about its uses. His e-mail address is on the schematic. I think he said it is used to power 85V-250V TV's and fluorescent lights.
  17. audioguru2

    Switching idea

    I can't explain it until I know how high and how low is the voltage swing of the PWM signal.
  18. audioguru2

    0-30 Vdc Stabilized Power Supply

    The output voltage is reduced by the current regulator when the current-setting pot is turned down, and the load's current tries to exceed the setting of the current-setting pot. Maybe U3 is bad and causes heating. Try swapping it with another opamp.
  19. audioguru2

    pramplifier circuit

    Hi Mughal, Anything over 100k is too high for a pot as a negative feedback resistance because it will pickup interference. To get more gain, reduce the value of R4. 470 ohms will give a max gain of 214 and since the TL071 is wideband then its audio high frequency response is still fine. With 470...
  20. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Smit, U3 doesn't do much work so shouldn't get hot. You already checked that R20 is 10k but maybe it is painted wrong, measure its resistance. Maybe your pcb has a short on it. What is U3's output voltage? Your project should give more than 24V at 3A even though your transformer's voltage is...
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