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NE555: NE555 timer

shailendra sharma
Prodigy 20 points
Part Number: NE555

Sir, I am using NE555 timer for led drive. When press trigger led will ON for 15 min  and then OFF . My problem is  led ON in starting without press the trigger button. I want to need led should ON whenever press trigger button.

  • 0
    TI__Guru**** 154026 points
    Shailendra,

    Is your circuit close to figure 9 in the NE555 data sheet? RL is not required.

    I believe you said the the output goes high when the power supply turns on. Does trigger (pin 2) voltage equal the Vcc (pin 8) voltage on power up? If trigger voltage is less than VCC then the output may trigger on power up. Keeping output low during power up can be achieved by adding a capacitor from Reset (pin 4) to ground and a charging resistor between Reset (pin 4) and Vcc (pin 8). The low input on reset during power up will ensure that the output starts low.