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  1. K

    RF coupling transformers

    I have read the explaination for impedance matching and transformers. In what kinds of circuits are they used, and why use a transformer?
  2. K

    Portable charger?!

    In defense of the product, since it must work, it seems useful. My cell phone is nearly always fully charged and takes only minutes to recharge with an AC charger. Plus, you can maintain a full charge without access to a power outlet. The circuit must be power efficent and could include a...
  3. K

    RF coupling transformers

    I did a Wikipedia search for impedance matching transformers. Still, it is about impedance matching. I was refering to transformers used in the IF frequency ranges of audio and video.
  4. K

    Balancing dual secondary rails

    I wouldn't be sure that you can connect the positive rail to the negative rail because the circuit is using bridge rectifiers. A lot of power supplies use rectifier dioides, and the peak inverse voltage rating of the diode can't be exceeded.
  5. K

    Balancing dual secondary rails

    A single transformer with many different secondaries could cause voltage problems. I think the power supply would need to be designed around it. It may be that additional secondary loading could be beneficial if it delivers the desired voltage and makes the design easier.
  6. K

    RF coupling transformers

    Impedance matching transformers don't match impedances at RF frequencies.  RF range transformers used for signal coupling are often step down transformers which increase load impedance, or they are used mainly for resonance. But they are hardly ever used in many circuits. Is it because they...
  7. K

    Making switching NPN with PNP

    It may be better to use a relay. If you need faster switching, you might try a shunt circuit with a MOSFET controller.
  8. K

    RF coupling transformers

    Do RF coupling transformers ever step up or step down voltage? I have only seen them used in a few applications. Are they inefficient signal coupling devices?
  9. K

    question about symetrical swing

    I'm sorry, that formula is not correct.  But the collector voltage is increased because of the saturated transistor voltage drop, if any, and the emitter resistor.
  10. K

    transistor biasing

    A 2N3904 at 100mA may have a beta of 30, but I guessed it to be closer to 100. The power dissipation was within 100mW of it's maximum. A transistor with a 3A maximum current rating can have a minimum beta of 30. Doesn't that rating apply to any bias voltages?
  11. K

    transistor biasing

    Since the collector current reduces with an increasing voltage, the load current increases. Can't a 2N3904 handle at least a 100mA load at all? So the base current would at least be 500uA.
  12. K

    thesis

    I don't know if that is a good thesis. Assuming it is a thesis for an Electrical Engineer, you may want it to include a study in electrical reliability and materials cost for certain projects.
  13. K

    Parallel LC

    How good of an oscillator frequency measurement device can a parallel LC be? The peak voltage would occur at the resonant frequency. Is there an easy way to determine peak voltage?
  14. K

    transistor biasing

    If a 2N3904 has a base bias bias current of 4.3uA, then it would need a high impedance load. A base current of 500uA would be needed for a lower impedance load. So isn't 4.3uA base current a bias intended for high impedance loads?
  15. K

    question about symetrical swing

    A saturated bipolar transistor can have a voltage of .3volts. That is VCE. VC, or colector voltage would be .5Vcc + .3volts. But normally, the saturation voltage is near 0volts. In biploar transistor digital logic, the maximum logic low level is .8volts.
  16. K

    question about symetrical swing

    Approximately .5Vcc is the optimum collector voltage for maximum voltage change. A bipolar transistor can however drop as much as .3 volts, which means the collector voltage would need to be .3volts higher.
  17. K

    How does this simple circuit operate?

    Well of course. It's an interesting circuit which Steven has built and works. It is difficult to expect circuits to function unless the component values are exact and the design accounts for component tolerances.
  18. K

    varactor diodes

    A 200pF capacitor can discharge relatively slow with a large resistance. But they always look cheaply made. I doubt some of them even function in some electronics products.
  19. K

    How does this simple circuit operate?

    Instead of an LED, could you use a diode and a small light bulb in series? Maybe a single 1.5V battery to power the small bulb? It looks like the component values would be difficult to determine in order to get it to oscillate.
  20. K

    How does this simple circuit operate?

    Hello Walid, I have never seen an LED in parallel with a 2N3904 transistor. Does it have current gain, voltage gain, or both? The power source doesn't have a voltage value.
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