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  1. walid1

    Transformerless power supply discussion!

    Hi guru (1) the word "at the moment" is the problem if we agree that the voltage reaches 311 volt 100 times per a second that is every 1/100 sec the voltage value is 311v in the human sense it is every time, every any bit of time.......... (2) in this circuit there is no resistor to limit the...
  2. walid1

    Transformerless power supply discussion!

    hi please look at the following circuit, it is a transformerless power supply: this is a 12 volt and can supply a max current = 15 mA I calc this current as: Xc = 1/2 pi f C = 14.47 K ohm I = (220 -12 - 1.4)/Xc = 15 mA the 1.4 volt is the drop voltage on two diodes Now, please tell me What...
  3. walid1

    Logic gates question

    Hi everybody If i have 4 inputs (logic 1 or 0) What logic gates must be to light a lamp if only two (any two) of the input is at logic one? THANKS
  4. walid1

    trasformerless powersupply

    Hi
  5. walid1

    Hearing aid circuit

    Hi guru No, the circuit worked i built it 3 times for me and for some frinds it was very very sensitive to voice it picks a very very low voice at night i put it and hear persons speak with eachother, Believe me. the only change i do, it was by a chance, is that it operate very well with one not...
  6. walid1

    Hearing aid circuit

    Hi sarma What is the 0.9V? Why? Hi guru I read somewhere that the Q1 stage voltage gain = approx. R2/R1, with R2 = 680K Av= 680/3.3 = 206, where at R2=10, Av = 3 only?????? No it is biased through R7 = 100K please explain it more. I enjoy seartching the errors I'm sure it is a hearing aid...
  7. walid1

    Hearing aid circuit

    Hi for the following circuit if i replace R2 by 10 k and C3 by 10u what would youy expect. someone told me that the circuit operate fine it is a hearing aid thanks
  8. walid1

    OVER-/UNDER-VOLTAGE PROTECTION CIRCUIT ANALYSIS

    Hi guru BC547 max allowed collector current is 500mA and not 100mA BC327 is pnp tansistor and not npn 2N4401 is 1000mA but the same power of 625mW here is a table of some suggested transistors, i see all are suitable. thank you guru
  9. walid1

    OVER-/UNDER-VOLTAGE PROTECTION CIRCUIT ANALYSIS

    hi guru It is very good answer. I read somewhere that op-amps designed to be a comparator has an o/p stage like open collector transistor or a darlington pair. is this true? AND what is the frequency compensation ? No thanks I found it in: http://en.wikipedia.org/wiki/Frequency_compensation...
  10. walid1

    OVER-/UNDER-VOLTAGE PROTECTION CIRCUIT ANALYSIS

    Hi For a comparator : What will be the form of the o/p when exactly equal voltages applied on the inputs. Also, what the less difference between the two inputs to turn the o/p of the comparator to another, thank you for your attention
  11. walid1

    OVER-/UNDER-VOLTAGE PROTECTION CIRCUIT ANALYSIS

    Thank you Sarma but please what the meaning of zee? thanks
  12. walid1

    OVER-/UNDER-VOLTAGE PROTECTION CIRCUIT ANALYSIS

    Also here in Gaza every day hear that some devicewas burned because of Electricity . Thank you very much
  13. walid1

    The caps surrounding the LM7812 regulator?

    Hi guru First, thank you very much I swear I read it, but I do not understand, they put figures and curves and I want rules like what you learned me Your answer almost picture more, While it is good to draw my attention to the Datasheet thank you guru
  14. walid1

    OVER-/UNDER-VOLTAGE PROTECTION CIRCUIT ANALYSIS

    Hi I understand that the voltage of 240 volts is a danger to the fridge , But I do not understand how the voltage when is less than 180 volts risk it. Can you please explain that to me? God bless you and thank you
  15. walid1

    The caps surrounding the LM7812 regulator?

    Hi guru Tell me please, what could happen if we remove them, Are they very essential. I mean what the damage caused by the absence of these caps. Second question : If you have a 12V voltage regulator in a circuit. How must be the least value of the i/p DC voltage to get a 12-volt at the o/p...
  16. walid1

    The caps surrounding the LM7812 regulator?

    Hi guru Thank u for reply please what the differance between ringing and oscillating? thanks
  17. walid1

    The caps surrounding the LM7812 regulator?

    I am waiting for the answer, a little patience be useful.
  18. walid1

    The caps surrounding the LM7812 regulator?

    Hi please look at the attached figure below: u can see two caps around the LM7812 I go to datasheets and read about them, After read that I felt I did not reach the result required. can you explain it more fore me Thank you for your cooperation
  19. walid1

    OVER-/UNDER-VOLTAGE PROTECTION CIRCUIT ANALYSIS

    Dear guru: Give me an example (names) of that op-amps. I Know the o/p high = Vcc – 1.2V, but don’t know the o/p Low = 10mV? I want to make a calculation, Let  R = 330 ohm 12V – I * 330 – 1.8V – 0.2V =0 I = 10/330 = 30 mA If we choose R = 470 ohm I = 10/470 = 21 mA If we choose R = 1K I =...
  20. walid1

    OVER-/UNDER-VOLTAGE PROTECTION CIRCUIT ANALYSIS

    Hi guru I understand from your words that there is no problem in the value of the R4 (=1K) resistance. And all of the problems resulting from a lack of a current limiting resistor in series with the LED. I am now comes over as I feel I did not understand anything. At the outset I thought I...
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