Need help with this transistor question...

Discussion in 'Homework Help' started by allhuber, Feb 26, 2012.

  1. allhuber

    Thread Starter New Member

    Nov 5, 2011
    12
    0
    Hi AAC,

    need help with this question:

    In Figure B1, the thermistor, RTH, has a resistance of 75k at 0°C and 25k at 100°C. At 100°C, the transistor reaches its saturation with Vce(sat) = 0.2V and LED is turned on. At 0°C, the transistor is cut-off and LED is turned off. Given that: VLED is 1.8 volts when forward-biased,  = 80 and VBE = 0.7 volt.
    Determine:

    -The minimum voltage of Vb for saturation to occur; (5 marks)
    -The minimum value of R1 for the circuit to operate. Show also that at 0° with the calculated value of R1, the transistor is cut off / conducting.

    [​IMG]

    THANKS ALOT!!!
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    You need to post what you've worked out so far. For example an estimate of the LED / Q1 collector current when the transistor is in saturation.
     
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