sinkng and sourcing currents in TTL NOT

Discussion in 'General Electronics Chat' started by haditya, Feb 12, 2004.

  1. haditya

    Thread Starter Senior Member

    Jan 19, 2004
    220
    0
    hii
    could anyone tell me what exactly are sinking and sourcing currents inn TTL
    i need to know their defn and their practical application..
    i seem to have a difficulty understanding it
    thank u
     
  2. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    143
    When chip outputs are said to 'sink' or 'source' current it refers to the direction of the current at the chip's output. If the chip is sinking current it is flowing into the output. This means that a device connected between the positive supply (+Vs) and the chip output will be switched on when the output is low (0V).

    If the chip is sourcing current it is flowing out of the output. This means that a device connected between the chip output and the negative supply (0V) will be switched on when the output is high (+Vs).

    It is possible to connect two devices to a chip output so that one is on when the output is low and the other is on when the output is high. The maximum sinking and sourcing currents for a chip output are usually the same but there are some exceptions, for example 74 series TTL logic chips can sink up to around 16mA but only source about 2mA.

    I will try and dig out a practical application of this. Hope that helps a little, post back if you need more help :)
     
  3. Battousai

    Senior Member

    Nov 14, 2003
    141
    44
    I guess this is kind of the same thing that Dave said, but in some texts they refer to pmos current mirrors as current sources and nmos current mirrors as current sinks.
     
  4. haditya

    Thread Starter Senior Member

    Jan 19, 2004
    220
    0
    thanks a lot
     
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