CMOS current source

Discussion in 'General Electronics Chat' started by simo_x, Aug 28, 2011.

  1. simo_x

    Thread Starter Member

    Dec 23, 2010
    200
    6
    Hi dears,

    I was wondering which is a typical current source value for a CMOS gate, for example I would like to source an NPN transistor relay driver..
    In the 4018 datasheet it marks negative values. I am little bit confused.. CMOS operates in saturation region so the RDS shouldn't be so great. Correct?

    Thank you.
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    In the datasheet you posted they indicate source current as being negative, and sink current as being positive. (the upper transistor which is conducting when output voltage is positive is a P-MOSFET) . That's not important, you know what current flow direction will be for each case. What matters is the absolute value.
    Figure 13 and 14 give you the relationship between output current and output voltage.

    Under "DC electrical characteristics" they also give examples of what would be the internal voltage drop depending on output current, e.g. for 15Vdd at 8.8mA your output voltage will be 13.5V (at ambient temperature). These are the recommended values , measured one output at a time. The maximum current is limited by maximum power dissipation.
     
  3. simo_x

    Thread Starter Member

    Dec 23, 2010
    200
    6
    Many Thanks ;) It's clear now.
    Bye!
     
  4. simo_x

    Thread Starter Member

    Dec 23, 2010
    200
    6
    Nothing.. Sorry
     
    Last edited: Aug 28, 2011
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