Calculateur de Timer 555 Monostable
Calculez la durée d'impulsion d'un 555 monostable.
V
V
kΩ
kΩ
Upper Trip Point
2.727 V
Lower Trip Point2.273 V
Hysteresis Band0.455 V
Upper Trip Point vs Reference Voltage
Formule
## Comparator Hysteresis Positive feedback adds hysteresis to prevent output chatter on noisy signals. ### Formulas **V_upper = V_ref + (V_out_high - V_ref) x R2 / (R1 + R2)** **V_lower = V_ref - V_ref x R2 / (R1 + R2)** **Hysteresis = V_out_high x R2 / (R1 + R2)**
Exemple Résolu
Vref = 2.5 V, output swings to 5 V, R1 = 100k, R2 = 10k.
- 01Upper = 2.5 + (5 - 2.5) x 10/110 = 2.5 + 0.227 = 2.727 V
- 02Lower = 2.5 - 2.5 x 10/110 = 2.5 - 0.227 = 2.273 V
- 03Hysteresis = 5 x 10/110 = 0.455 V
Questions Fréquentes
Why add hysteresis?
Without hysteresis a comparator oscillates rapidly when the input hovers near the threshold due to noise.
How much hysteresis do I need?
The hysteresis band should be wider than the expected noise on the input signal.
Is this the same as a Schmitt trigger?
Yes, a comparator with hysteresis is functionally a Schmitt trigger.
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