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Discussion in 'Electronics Homework Help' started by nik311296, Feb 10, 2013.

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  1. nik311296

    nik311296

    4
    0
    Feb 10, 2013
    Could someone help me with an exercise that I got in school.
    I have attached the schematics.
    The upper VCC = 15V, and the lover VCC = 0V.
    R1 = 4,7 Kohms, R2 = 47 Kohms and R3 = 150 Kohms.
    I need the value of Ic (current trough collector) and Vce (voltage between Emitter and Collector).
    I need a step by step explanation how we get to the results.
    Thank you!
    10-2-2013 11-12-07 PM.jpg
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
    2,837
    Jan 21, 2010
    Both are labelled Vcc, so they should be the same voltage (either that or label them Vcc1 and Vcc2). If it is 0 volts, then it is gnd.

    You need to know the gain of the transistor to answer this question.
     
  3. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    Start by writing down what you know about the circuit. A standard assumption is for the voltage at the base of T1. Then the current flowing into the base comes through R2 and R3. I3=(Vcc-Vb)/R3. I2=(Vce-Vb)/R2. So Ib=I2+I3 and with the transistor gain, B, Ic=B(Ib). And finally Vce=Vcc-(Ic+Ib)R1. So just solve for Vce in terms of B. Then estimate a reasonable value for B (you will never really know what it actually is - and if you measure B accurately, just wait a bit and it will change.) You should find that the higher the value of B, the less effect a variation in B will have upon the bias point of T1.
     
  4. nik311296

    nik311296

    4
    0
    Feb 10, 2013
    Thank you for the help!
     
  5. nik311296

    nik311296

    4
    0
    Feb 10, 2013
    I will send you when I get back from school more details so you could analyses them.
     
  6. nik311296

    nik311296

    4
    0
    Feb 10, 2013
    I have created an advanced version of the schematic.
    So here is the rest of the data : R1 = 4.7K, R2 = 47K, R3 = 150K.
    I need the rest of the data and especially Ic.
    So could you please again write the solution step by step for the task. 10-2-2013 11-12-07 PM.jpg
     
  7. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    So did you write down what you know about the currents flowing in this circuit? How do the currents relate to the node voltages? What value of gain will you use for T1? How many unknown variables are there? How many independent equations will you need for a solution?
     
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