TIDUFE6A September 2025 – December 2025
The digital input connects a safety switch, monitors relay feedback signals, or reads other logic-level states. The input signal first passes through a 10kΩ series resistor that limits the current, followed by a Zener diode that clamps the voltage to 5.1V. A filter capacitor connects parallel to the Zener diode to suppress transients caused by the Zener diode switching behavior.
The protected signal then feeds into a Schmitt-trigger buffer, the SN74LVC1G17. The buffer accepts input voltages up to 5.5V, even when powered from a lower supply voltage. In this configuration, the circuit can safely accept logic inputs up to 24V. The SN74LVC1G17 hysteresis characteristics, with a positive-going threshold of approximately 1.8V and a negative-going threshold of 1.3V, prevent false triggering caused by noisy or slow-changing signals.