please explain this IR circuit

Discussion in 'Analog & Mixed-Signal Design' started by jack hammer, Aug 15, 2016.

  1. jack hammer

    Thread Starter New Member

    Jan 25, 2016
    3
    0
    Hi
    I have 2 questions about it.
    1. I understood reason why emitter of TR2 and base of TR3 was connected.
    but I can't understand reason why base of TR3 and emitter of TR4 was connected with R11.

    2. how was c5, c6 capacitor value selected?

    please explain this reason!:)
     
    • ca.PNG
      ca.PNG
      File size:
      33 KB
      Views:
      37
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,978
    744
    Tr3/4 are wired as a schmidt trigger, tr3 is turned off by R11 when Tr4 is on. This is to give a snap action on the relay.
     
  3. jack hammer

    Thread Starter New Member

    Jan 25, 2016
    3
    0
    thanks !
    i tested this circuit without R11 connection.
    but circuit worked well.
    i think emitter of TR2 and base of TR3 connection sufficiently play a role as TR4 trigger.
     
Loading...