BJT and PMOS switch question

Discussion in 'Homework Help' started by jerome89, Nov 7, 2013.

  1. jerome89

    Thread Starter New Member

    Jan 14, 2013
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    [​IMG]
    R1 to R6 is 470 ohm
    Vdd is 20v
    the arrow is connected to gate of PMOS, PMOS is sharing the same Vdd 20v

    may i ask, why is there no resistor on the base of NPN ? if theres one, what is it used for ?
    what is the purpose of R1 to R6 resistor?

    sorry, my electronics is really horrible, i hope you can clear my doubt
    thanks
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    1,103
    The ULN2003 has Darlington transistor outputs, each with an in-built 2.7k base resistor.
    R1-R6 are collector loads acting as pull-ups.
    I can see no purpose for Q1-Q6 unless they merely represent the ULN2003 output transistors.
     
  3. jerome89

    Thread Starter New Member

    Jan 14, 2013
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    yes uln ports connected to pic microprocessor
    why R1-R6 is 470 ohm and not higher or lower?
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Ask the circuit designer. What does the PMOS switch control?
     
  5. jerome89

    Thread Starter New Member

    Jan 14, 2013
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    a BLDC motor
     
  6. ScottWang

    Moderator

    Aug 23, 2012
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    Maybe this is what you want.
    [​IMG]
     
  7. jerome89

    Thread Starter New Member

    Jan 14, 2013
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    erm i want to understand how it works from the graph i am showing, thanks !
     
  8. ScottWang

    Moderator

    Aug 23, 2012
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    But the circuit is wrong.
     
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