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walid

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Posts posted by walid

  5. transistor as a switch

    in Theory articles

    Posted

    To guru
    thank u very very much you are good and expert man.

    hi, just wondering, what does this circuit do?
    is it just to change the output voltage of the 555?
    if so what does the transistor for?

    this is a part of a circuit shown in the following link:
    http://www.electronics-lab.com/forum/index.php?topic=10229.0
    it is an IC controlled emergency lamp with charger

  10. IC controlled emergency lamp with charger

    in Theory articles

    Posted

    Hi guru

    The article says that D5 adds to the zener's voltage for a 6.9V reference which is higher than the battery.

    I am very sorry, I did not notice it. How wonderful it for a zener non-existent

    D8 bypasses R4 when the 555 timing capacitor charges so it charges quickly.

    My understanding is that the cap charged through only R3, but now I do not know how dischargting, or to any point, is it to  pin is 6 or 7 of the 555 IC.
    and why he do so, what shape of the o/p pulse he want? please explain it for me.

  12. Adjustable precision shunt regulators, TL431

    in Theory articles

    Posted

    Hi
    I have another question about the shunt regulator 431:
    We Know that Vout = (1 + [R1/R2]) * Vref
    If I want Vout 12.5V and assume Vref = 2.5V then 12.5/2.5 = 5
    that is R1/R2 =4
    400K/100K = 4
    4ohm/1ohm =4 ???!!!!!
    I read three different 431 datasheets from three different companies trying to find something about the values of that resistos, but nothing.
    can u please help
    thanks

  17. transistor saturation

    in Theory articles

    Posted

    hi guru
    You did not understand me, so I'll ask the question once again :
    The 2N3904 transistor have the following char. from datasheet:
    Po = 625 mW
    Ic max = 200 mA
    VEC max = 40 V

    from that, if we have VCE = 5V, the max IC = 625m/5= 125 mA

    Now if at saturation, VCE=0.4 V, then Ic max = about 1.6 A

    my question now, can i use a load draw 1.5A in a swtching circuit using 2N3904
    thanks

  18. transistor saturation

    in Theory articles

    Posted

    Suppose that You used a transistor 2N3904, in its datasheet I found that the Po = 625 mW; the power which this transistor can dissipate (in the form of heat) equal to 625 m Watt. Now, if we assume that VCE = 0.4 V at saturation, this transistor can pass to 1.5 ampere as Ic.
    But in the datasheet Ic max = 200mA
    I read from this page:
    http://www.kpsec.freeuk.com/trancirc.htm
    that:
    The power developed in a switching transistor is very small:

    In the OFF state: power = Ic × VCE, but Ic = 0, so the power is zero.
    In the full ON state: power = Ic × VCE, but VCE = 0 (almost), so the power is very small.

    can you explain to me to what value of Ic I can operate this transistor.
    thank you.

  21. Crystal examiner

    in Theory articles

    Posted

    Hi
    often have some friends with their remote control to to repair it. This requires that you have the examiner Cristal to ensure the validity of this piece. In the past, I was immediately replaced them with new, but I know I need to examine the crystal. Searched in the internet and I found this circuit and structure but did not work, therefore decided to understand it very well that to succeed when structure the next time.
    I deleted the 56p cap because I do not need to watch the freq. I know that the first transistor worked as oscillator and the o/p sig rectified by the two diodes to the final stage which will be ON if the first stage oscillate.
    My questions:
    1) is the 1st stage is colpitts osc.
    2) How the value of frequency depends on crystal?
    3)Why 680p and 150p caps, What if others these values? 

    post-2833-14279143277696_thumb.jpg

  22. Help me to understand the MC3359P IC

    in Theory articles

    Posted

    Hi guru
    thank you for fast reply

    I don't know why your phone uses a power transistor for its RF driver or output since the power is very low.

    In my country, there is a puplic open market, they sold scrap, half a telephone 1/4 radio part of vedio recorder..etec
    every month, i go to this market any by some boards
    i have this 1/2 phone, it is senao, it is at least 10 km long.

    After this discussion with you, now i don't want to take parts of this phone and reconstruct it to a Tx and Rx. but you open my eyes to new things merit to look at and discuss
    i gained till this moment some important information about narrow and widebands and can imagine now how modulation process takes place (sorry for bad grammar)

    Now my cordless phones are 900MHz and much higher frequency ones are sold now

    Why manufatures go to a higher freqs, is it better?

    The 1st generation used 27MHz (CB or Citizen's Band) for one frequency and 1.7MHz (if I remember correctly) for the other frequency. One is AM and the other is FM but I can't find out which was which.

    this is a good information and from it i can diduce that mine is transmit at 1.7MHz AM and receive at 27MHz FM.

    CB or Citizen's Band

    what the range of freqs of Citizen's Band?

    at this time I'm near to finish the drawing of the o/p section starting from the antenna, the filter is very complex series and parallel combinations of caps and air coils (look at the last photo), i'll put it here to discuss it with u to learn new things.

    thank you guru

  23. Help me to understand the MC3359P IC

    in Theory articles

    Posted

    Hi guru
    Ok, I understand that you have never looked inside one before and u have never seen a schematic of a narrowband dual conversion FM receiver circuit before. But also I know that u still have the ability to help me. I need you theory information to help me in my trip inside that cordless phone.
    I the fiq below, I’ll concentrate on the 2sc2314 transistor, in its datasheets I read: 27MHz CB Transceiver Driver Applications
    1) What the meaning of CB?
    2) Is 27MHz mean that the operating freq of both TX and Rx is 27MHz?
    3) What you understand from using that transistor?

    Thank you

    post-2833-14279143272281_thumb.jpg

    2sc2314.pdf

  25. Help me to understand the MC3359P IC

    in Theory articles

    Posted

    Hi guru

    I don't know how you are going to design a narrowband dual conversion FM radio without a schematic.

    dont worry I'll draw the schematic and discuss it with you.

    It needs a double-sided pcb with a ground plane over most of its surface.

    I can do it, u  help me, we can do it.

    now i'll draw the Rx (3359) and related parts and put it here, then u tell me where the TX part
    I see the two LM567CN, i know they are for tone detection
    I'll draw all pars in sequance and discuss them with you
    guru I want to work hard and I need you help what u say???
    yours Walid
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