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  1. audioguru2

    0-30V Stabilized Power Supply

    I have a Redwire schematic 5/04/2008 that is missing how the current-setting pot is connected. In my version, opamp U3 is a TLE2141 that has a max input offset voltage of only 1.4mV. R17 is 33 ohms and is connected at the lowest voltage pin of the current-setting pot to make a voltage of 5.6mV...
  2. audioguru2

    AM modulator with MC1496 project problem

    The circuit you found is different to the AM Modulator circuit shown in Motorola's datasheet for their MC1496. Use the circuit in the datasheet.
  3. audioguru2

    how can stabilize the mosfet's drain current help (linear amplifier)

    Each Mosfet dissipates (12V x 0.4A)= 4.8W. When a Mosfet gets hot then its current reduces and only increases when it melts. Maybe your heatsink is too small.
  4. audioguru2

    0-30V Stabilized Power Supply

    The latest circuit works only with MC34071 or TLE2141 opamps. Their max allowed supply is 44V while most 741 opamps have a max allowed supply of only 36V. The latest circuit has a negative supply of only 1.3V and the required opamps work fine but a 741 opamp needs at least -3V to -5V for a...
  5. audioguru2

    Inverting Op Amp

    The inputs of a 741 opamp must be at least 3V more positive of pin 4. Your input pin 3 is the same voltage as pin 4 so its input transistors are completely turned off all the time. Bias pin 3 at +3V with two resistors then the opamp will have an output high voltage of +10.8V and an output low...
  6. audioguru2

    0-30V Stabilized Power Supply

    Hi No Worries, I cannot see how your transistors are connected. Is "OL" on your ohm-meter a very high resistance? The 2N3055 output transistors are emitter-followers. Their emitter voltage is 0.4V to 1.0V less than their base voltage. The BD139 driver transistor is also an emitter-follower. Its...
  7. audioguru2

    Infrared cordless Headphone Amplifier help please

    It is mono. If you want stereo then use two different carrier frequencies like 100kHz and 180kHz.
  8. audioguru2

    UPS or inverter

    2kV is a voltage, not a power. W is Watts which is power. Do you want a max power of 2kW? It is impractical because the current from the 12V battery will be an average of 175A and the peak current from the battery will be 247A. A battery will boil or explode.
  9. audioguru2

    Infrared cordless Headphone Amplifier help please

    I looked in Google for Infrared FM Headphones Circuit and found many circuits. Most use AM instead of FM and some are similar to the one you found that won't work. For the FM transmitter, the VCO of a CD4046 phase-locked-loop IC is used and another CD4046 is used as an FM detector.
  10. audioguru2

    Infrared cordless Headphone Amplifier help please

    Nope. It is a hopeless circuit designed by somebody who knows nothing about electronics. The first transistor in the transmitter is not even biased! It rectifies instead of amplifying. Have you ever heard a rectified audio signal? It has more than severe distortion. The red LED in the...
  11. audioguru2

    basic question Leds and Diodes Resistor hook-up

    LEDs are not made accurately. They have a range of forward voltage that is 2.8V for one then 3.6V for the one beside it. Their average is 3.2V. So you must limit the current instead of feeding a regulated voltage. The spec's for most little LEDs show a max current of 30mA so use 20mA. With a...
  12. audioguru2

    0-30V Stabilized Power Supply

    Without any negative feedback then opamp U2 will have a input voltage but no output feedback so its gain of about 200,000 will force its output as high as it can go. Remove the output transistors then short their base-emitter terminals for the driver transistor and U2 to work properly and drive...
  13. audioguru2

    High voltage power supply - need help

    The high voltage power supply is extremely dangerous! It might kill you. It uses a high voltage power transistor, not a low voltage 2N3055 transistor.
  14. audioguru2

    0-30V Stabilized Power Supply

    The driver transistor and the output transistor are simple emitter-followers. The base voltage is the input and the emitter voltage is the output which is about 0.7V less than the base voltage if the project has a load of about 100mA. The collectors of the transistors are connected to +41V so if...
  15. audioguru2

    question about Low Pass Filter

    The 4.7nF capacitor creates a lowpass filter with the unknown value of the source resistance. The 10k resistor and 6.8nF capacitor create another lowpass filter. If the cutoff frequency of both filters is the same then their total is -6dB because each filter is -3dB.
  16. audioguru2

    Constant current battery charger

    Your very simple circuit is simply a constant current source, not a battery charger. A battery charger circuit will limit the voltage to whatever is required. Another LM317 can be added after the constant current LM317 to limit the voltage but it also needs an additional minimum voltage to work.
  17. audioguru2

    0-30V Stabilized Power Supply

    Ho No Worries, The output transistors or driver transistor are shorted or have their pins mixed up. The current-limiting LED should not be turned on when there is no load so it is another problem. The voltage pot should have an output from 0V to 11.2V. R5 plus R6 should have 11.2V. R5 should...
  18. audioguru2

    zener diodes

    The datasheets for zener diodes list their output impedance that is no where near as low as a voltage regulator circuit. A zener diode is a shunt regulator that wastes its entire max output when it has no load. Its voltage drops when loaded because it has no high gain error amplifier like used...
  19. audioguru2

    zener diodes

    A voltage regulator circuit has a zener diode voltage reference plus an error amplifier that drives the load. The zener diode voltage reference always has a constant load current. The error amplifier has the variable load current. A zener diode is a shunt regulator so its current is fairly low...
  20. audioguru2

    zener diodes

    A zener diode is used as the voltage reference in a voltage regulator, not for biasing. Constant current sources, current-mirrors and resistors (accurate ratios) are used for biasing. The zener diode is temperature stable when its voltage is 5.6V to 6.2V. For a higher stable voltage then it is...
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