555

Do you mean one of these? Here are quick notes you can use for exam prep. Pick whichever you want and I’ll expand.

• 555 timer IC (electronics)

  • Core: two comparators, SR latch, discharge transistor; outputs can source/sink up to supply.
  • Astable mode: no trigger input; frequency
    • Th = 0.693 (R1 + R2) C
    • Tl = 0.693 R2 C
    • T = Th + Tl = 0.693 C (R1 + 2R2)
    • f ≈ 1 / (0.693 C (R1 + 2R2)) ≈ 1.44 / (C (R1 + 2R2))
  • Monostable mode: triggered by a negative pulse; output stays high for T = 0.693 R C
  • Common notes: Vcc typically 5–15 V (depending on variant); control pin 5 decoupled; pinouts vary by package.
  • Quick example: If R1 = 1 kΩ, R2 = 10 kΩ, C = 100 nF, then Th ≈ 0.693×11k×100nF ≈ 762 µs, Tl ≈ 693 µs, T ≈ 1.455 ms, f ≈ 686 Hz.

• 555 in Roman numerals

  • 555 = DLV (since 500 = D, 50 = L, 5 = V)

• Prime factorization

  • 555 = 3 × 5 × 37

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