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SN74LVC1G74: what is the status of Q and Q# after first power up? pls help check the bellow circult

general king
Prodigy 81 points
Part Number: SN74LVC1G74
Other Parts Discussed in Thread: TPS3808

i use tps3808 and sn74lvc1g74 to control a power on/off. see the figure. i am not sure the status of Q/Q# after power on. could you clarify?

  • 0
    Prodigy 81 points
    PS: J49 connect to a bush button, U116.B connect to ATX_PS_ON signal, i want to achieve this function.
    1) after vdd_5vsb power on, the U114.Q should be "0", then U116 is off. the ATX power is off.

    2) press push button. the atx power on.

    3) press push button again, the atx power off.

    .......
  • 0 in reply to general king
    TI__Genius 16735 points
    Hello,

    Based on your setup, on startup the PRE is High and CLR is LOW. This means that on start up Q is Low. Then based on your R3500 value and C3709 Value, the CLR pin will go to a H with a 2.2RC delay. Once this happens, the flipflop will be powered up.

    Then with every positive clock pulse triggered by your push button the system will turn off and on.
    Here is a logic minute video explaining how to convert a momentary switch to a toggle using a flip flop.
    training.ti.com/TLM-APP-ToggleSwitch

    Thanks!
    - Karan