This calculator first finds the exact resistor values to give the required circuit parameters of an Inverting Schmitt Trigger and then allows the substitution of preferred resistor values or those readily available to find the resulting circuit parameters.

There are an infinite number of possible resistor values that will give the required High Trigger Threshold Voltage and the Low Trigger Threshold Voltage in an Inverting Schmitt Trigger because they are simply a ratio. Therefore, the required Maximum Reference Input current has been made selectable in order to set the required finite resistor values. The following formulas have been derived by myself and may not be in their simplest form.

Using the fact that both inputs to the op-amp will have virtually the same
voltages, we first calculate the value of the Reference Input Resistor (R1) from the Reference Voltage (V_{ref}) less the Low Threshold Voltage (V_{tl}) divided by the
the selected Maximum Reference Input Current (I_{refmax}).

Formula 1.

Formula 2.

Formula 3.

Formula 4.

Formula 5.

Formula 6.

First published on chemandy.com by W J Highton on 15/6/2018

This calculator is provided free by Chemandy Electronics in order to promote the FLEXI-BOX

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