What Is the Schmitt Trigger Hysteresis & Threshold Voltage Calculator?
A Schmitt trigger is a bistable comparator circuit where positive feedback creates distinct threshold voltages for rising and falling inputs.
How Does the Schmitt Trigger Hysteresis & Threshold Voltage Calculator Work?
The feedback resistor divider sets two switching levels: V_TH and V_TL. The difference V_H = V_TH - V_TL is the hysteresis bandwidth.
Schmitt Trigger Hysteresis & Threshold Voltage Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
V_{\text{TH}} = V_{\text{ref}} + \frac{R_1}{R_1 + R_2}(V_{\text{OH}} - V_{\text{ref}}), \quad V_{\text{TL}} = V_{\text{ref}} + \frac{R_1}{R_1 + R_2}(V_{\text{OL}} - V_{\text{ref}}), \quad V_H = V_{\text{TH}} - V_{\text{TL}}
Positive feedback hysteresis divider generates discrete switching trip points V_TH and V_TL to reject input noise in analog comparators.
How to Use the Schmitt Trigger Hysteresis & Threshold Voltage Calculator
- Select inverting or non-inverting circuit configuration.
- Enter output high and low saturation voltages.
- Specify resistor values R1 and R2, and reference center voltage.
Step-by-Step Example Calculation
5V Single-Supply Inverting Schmitt Trigger (R2 = 100k, R1 = 10k)
Input Values:
topology:inverting
supplyHighVoltageV:5.0
supplyLowVoltageV:0.0
feedbackResistorR2Kohms:100
inputResistorR1Kohms:10
referenceVoltageV:2.5
Worked Steps: Upper threshold V_TH is 2.727 V and lower threshold V_TL is 2.273 V, creating a 455 mV hysteresis noise immunity band.
Understanding Your Result
Hysteresis Voltage (V_H): Peak-to-peak noise amplitude the circuit rejects without chattering.
V_TH / V_TL: Precise voltage trip points.
Factors That Affect the Result
- Ratio R1 / R2 dictates the hysteresis window width; higher R2 tightens the window, lower R2 widens it.
When Should You Use This Calculator?
- Cleaning up noisy sensor inputs, rotary encoder debouncing, zero-crossing detectors, and relaxation oscillators.
Assumptions & Limitations
- Assumes rail-to-rail comparator performance or known saturation output voltages.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Standard analog circuit theory voltage divider formulation.