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555 Timer

555 Timer. Pin configuration. The 555 timer consists of; Two voltage comparators A bi-stable flip flop A discharge transistor and a resistor divider network. Internal Circuit Of 555 Timer. 8. 4. +. +. 5. +. +. C1. 6. R D. Q. 3. Q. S D. 2. C2. 7. T. 1. 5K. 5K. 5K.

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555 Timer

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  1. 555 Timer

  2. Pin configuration • The 555 timer consists of; • Two voltage comparators • A bi-stable flip flop • A discharge transistor • and a resistor divider network.

  3. Internal Circuit Of 555 Timer

  4. 8 4 + + 5 + + C1 6 RD Q 3 Q SD 2 C2 7 T 1 5K 5K 5K VCC Reset Control Voltage VA Threshold Output Trigger VB Discharge DischargeTransistor GND RS-FF Voltage Divider Comparator

  5. VCC + + . + + RD V6 V2 RD SD 5 VA C1 6 <2/3 VCC <1/3 VCC 1 0 >2/3 VCC >1/3 VCC 0 1 C2 SD <2/3 VCC >1/3 VCC 1 1 2 . VB >2/3 VCC <1/3 VCC 0 0 5K 5K 5K The result for comparing 2/3 VCC Not permitted 1/3 VCC

  6. output T RD Q Q SD V6 V2 Q T <2/3 UCC <1/3 UCC 1 off >2/3 UCC >1/3 UCC 0 on <2/3 UCC >1/3 UCC 保持 保持 RD SD Q T 1 0 1 off 0 1 0 on remain 1 1 remain remain remain

  7. Monostable Multivibrator & Waveforms

  8. Monostable Multivibrator (One-shot) Operation +VCC 4 VCC 8 (Re) + + + + 5K R1 5 1 VA 6 1 C1 RD Q uO 5K SD 3 Q 2 C2 0 ui VB 5K 7 uC T 1 Steady state 0 1 1 Q=0 >2/3 VCC on (grand)

  9. +VCC 4 VCC 8 (reset) + + + + 5K R1 5 1 VA 6 0 1 C1 RD Q uO 5K SD 3 Q 2 C2 0 1 1 0 ui VB 5K 7 uC T 1 Monostable Multivibrator (One-shot) Operation Transiet state 0 Q=1 < 1/3 UCC off (grand)

  10. +VCC VCC 4 8 (reset) + + + + 5K R1 5 0 1 VA 6 0 1 C1 RD Q uO 5K SD 3 Q 1 0 2 C2 0 0 1 ui VB 5K 7 uc Q=0 T 1 Monostable Multivibrator(One-shot) Operation Steady state 1 Q=1 >2/3 VCC (grand)

  11. uC uO ui t t t 2/3UCC tp =RC ln3=1.1RC What is a monostable multivibrator? • With one stable state • Normally in its stable state,to change to its unstable state only when triggered • Once triggered,to remain in its unstable state for a predetermined length of time and then return to its stable state automatically

  12. Astable Multivibrator & Waveforms

  13. + + 8 UCC 4 + + 5K . R1 Q 0 5 . VA Q 1 0 0 C1 3 6 RD R2 uO 5K C2 SD . . 2 1 . VB 5K RD=1 + 7 uC SD=0 – T . 1 (grand) 2) Astable Multivibrator(Oscillator) charge 1 >2/3 UCC <1/3 UCC first uC=0 1 discharge

  14. uC uO +VCC 8 4 5 t t 6 2/3UCC R1 . uO 3 2 1/3UCC R2 7 . . 1 uC C tp1 =(R1+R2)C ln2=0.7(R1+R2)C tp2 =R2C ln2=0.7R2C T=tp1+tp2 =0.7(R1+2R2)C tp1 tp2 What is an astable multivibrator? Duty Cycle = tp1/T • With one stable state

  15. Applications using 555 timer • A light dimmer ; • A car tachometer • Traffic Lights ; • Infra Red (IR) remote control ;

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