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ENTC 3320

ENTC 3320 . 555 TIMER. 1. Gnd. 8. +Vcc. 2. Trigger. 7. Discharge. 3. Output. 6. Threshold. Reset. 4. 5. Control voltage. 555 Timer IC Timer. The 555 timer has essentially two modes of operation: Astable (free running) multivibrator and Monostable (one shot) multivibrator.

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ENTC 3320

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  1. ENTC 3320 555 TIMER

  2. 1 Gnd 8 +Vcc 2 Trigger 7 Discharge 3 Output 6 Threshold Reset 4 5 Control voltage 555 Timer IC Timer • The 555 timer has essentially two modes of operation: • Astable (free running) multivibrator and • Monostable (one shot) multivibrator 555 Timer

  3. Pin Functions • PIN 1 Ground--usually connected to ground. The voltage should be the most negative of any voltage appearing at the other pins. • PIN 2 Trigger--level-sensitive point to 1/3 VCC. When the voltage at this pin is brought below 1/3 VCC the flip-flop is set causing pin 3 to produce a high state. Allowable applied voltage is between VCC (pin 8) and ground (pin 1).

  4. Pin 3 Output--level here is normally low and goes high during the timing interval. Since the output stage is active in both directions, it can source or sink up 200 mA. • Pin 4 Reset--when voltage at this pin is less than 0.4 V, the timing cycle is interrupted returning the timer to its nontriggered state. This is an overriding function so that the timer can not be triggered unless reset is released (pin 4 > 1.0 V). When not used, connect to VCC.

  5. Pin 5 Control voltage--internally derived 2/3 VCC point. A resistor-to-ground or an external voltage may be connected to pin 5 to change the comparator reference points. When not used for this purpose, a capacitor-to-ground greater than or equal to 0.01 mF is recommended for all applications. • Pin 6 Threshold--level sensitive point to 2/3 VCC. When the voltage at this pin is brought greater than 2/3 VCC., the flip-flop is reset causing pin 3 to produce a low state.

  6. Pin 7 Discharge--collector of a transistor switch to ground (pin 1). It is normally used to discharge the timing capacitor. • Pin 8 VCC--the power-supply voltage connected here can range from 4.5 to 16 V with respect to ground (pin 1).

  7. Astable Multivibrator Reset Discharge Threshold Trigger

  8. The charge/discharge equation for a RC circuit is: The charging circuit is through RA, RB, and C.

  9. The discharging circuit is through RB and C.

  10. The duty cycle will always be greater than 50%.

  11. The charge equation for a RC one shot is:

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