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  1. walid1

    How this ps unit works??

    The circuit in the following figure (from: http://www.hobby-circuits.com/circuits/power-supply/dc-power-supply/891/variable-dc-power-supply) represents a variable power supply Transistor Q1 is npn type This was corrected in the following figure I have thought carefully about this circuit, but...
  2. walid1

    Impedance relation between 2 Bjts

    Thanks audioguru I am very happy with your presence and I hope to be in good health and happy in your life. I have read in a book "The art of electroncs" page 66, the following I take it most likely the first stage is a source of signal with internal resistance (Zout1), and the second stage...
  3. walid1

    Impedance relation between 2 Bjts

    Hi Hero999 At first I like to thank you on the fast of response I mean here is if the output impedance of the first stage = 10k and the input impedance of the second phase = 10k Are these two impedances connected in series or parallel? thanks alot
  4. walid1

    Impedance relation between 2 Bjts

    Hi, If there are two BJT small signal amplifiers (common Emitter) cascade connected using a suitable decoupling cap The first preamp has an o/p imeadance Zo, and the second has an i/p impedance Zin Now we have Zo and Zin and a cap betwwen them My question is: Is the connection series or...
  5. walid1

    LC and Oscillators

    Hi KevinIV, Have you ever design an oscillator? if yes, please tell me how with the related math thanks
  6. walid1

    Why prefer to use the center tap???

    I don't understand, please give me examples
  7. walid1

    27MHz colpitts oscillator qestion

    This circuit was intended as 27MHz colpitts oscillator: and whem simulated using multisim10 sofware I get: I have some questions: Any osci. Needs a FB to sustain oscillations, I think that this FB from collector to base path through the parallel two caps; the internal transistor capacitance...
  8. walid1

    LC and Oscillators

    Hi I noticed in many books that LC tank is connected to the base of the transistor, while connected to the collector in a real designs. Why this confusion? thanks
  9. walid1

    What does the 33uH coil in this circuit?

    sorry there is no respond
  10. walid1

    Why prefer to use the center tap???

    Often observed in many of the schemes that the circuit designer prefers to use the center tap as in Fig.(1) and not, as in Fig.(2), why? Thanks
  11. walid1

    What is the function of this circuit?

    http://www.sentex.ca/~mec1995/circ/at121.html
  12. walid1

    A 1n4148 diode makes the transistor on and off?

    I've built this emergency lighting circuit When the main voltage 230 V is present, LEDs turn off And when does not LEDs turn on Transistor and 1n4148 diode are responsible for making the LEDs turn off Question: How do the 1n4148 diode makes the transistor on and off? Thanks note: the...
  13. walid1

    Brightest White LED

    In fact, no one understand my question. I do not ask about the intensity of light, my question was about how to examine it. And to know whether is good or bad? Thanks
  14. walid1

    Is it bad design?

    thank you guru, yes the transformer is cheap
  15. walid1

    Brightest White LED

    How do measure the Brightest White LED and see if it is damaged or not? thanks Note: I have tried to test in the same way as the normal LED, but did not give me any reading from both sides
  16. walid1

    Is it bad design?

    What is the function R3 If you know that the output voltage at both ends of the 220u capacitor is 9 volts DC, is not this resistance wastes 9mAh all of time What is the point of that? thanks
  17. walid1

    questio: L-network

    I read in the book: RF Circuit Design, chapter 4 page 66 How can matching 1000 ohm source with 100 ohm load? thanks alot
  18. walid1

    Why caps in paralell?

    I understand from your words that if I had two caps, one of them is equal to 5p and the second = 10p. Better to use the two in parallel to get 15p and not one 15p to make an easy path for the high-frequencies toward ground???
  19. walid1

    Why caps in paralell?

    the caps at the right, why 10p//15p? what if use one 25p cap? thanks
  20. walid1

    How to distinguish between FM and AM transmitter circuits

    Hi Hero999 I try 4.7k and 470 ohm but the freq remain at 50 MHz I then changed the transistor to 2N3904 but it still 50MHz thank you
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