Schmitt Trigger Calculator
Calculate non-inverting Schmitt trigger threshold voltages and hysteresis band for comparator circuits with positive feedback.
Formula
Reference: Horowitz & Hill, "The Art of Electronics" 3rd ed.
How It Works
A Schmitt trigger is an electronic circuit used for signal conditioning, providing hysteresis to prevent rapid oscillation in analog signals. It creates a threshold with a deliberate dead band, which helps convert noisy or slowly changing analog signals into clean digital transitions. By introducing hysteresis, the circuit requires a different input voltage to switch on versus switch off, which reduces sensitivity to small signal variations.
Worked Example
Problem: Design a Schmitt trigger with Vcc = 5V, R1 = 10kΩ, R2 = 5kΩ, R3 = 2kΩ Solution: 1. Calculate Upper Threshold: Vth+ = 5V·10k/(10k+5k) + Hysteresis/2 = 3.33V + Hysteresis/2 2. Calculate Lower Threshold: Vth− = 5V·10k/(10k+5k) - Hysteresis/2 = 3.33V - Hysteresis/2 3. Calculate Hysteresis: Vhyst = 5V·5k/(5k+2k) = 3.57V
Practical Tips
- ✓Choose resistors to create appropriate hysteresis band
- ✓Consider temperature coefficients of resistors
- ✓Use precision resistors for more consistent performance
Common Mistakes
- ✗Incorrectly calculating resistor ratios
- ✗Neglecting power supply voltage variations
- ✗Using unsuitable resistor values for desired hysteresis
Frequently Asked Questions
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