What the SN7405N is and where it fits
The Texas Instruments SN7405N is a 7400-series hex inverter with open-collector outputs, packing six independent inverter gates into a single 14-pin DIP package. Each gate accepts one input and inverts it; the open-collector output means the high-side transistor is absent, so the output can sink current to ground but cannot source it — the load must pull up to a positive rail.
Key ratings and what they mean for the design
The open-collector output can sink up to 16 mA per channel when low, but the high-level current is zero — the external pull-up resistor determines the high-state voltage and the current sourced from the load supply.
Lifecycle and sourcing posture
ROHS3 compliance is confirmed, so it meets the latest EU restriction directive for lead and other substances. Because it is an active, standard-logic part, it is widely available through multiple distribution channels. No second-source alternate is listed in the official cross-reference data, but functionally equivalent hex inverters with open-collector outputs exist from other manufacturers — verify pin compatibility and timing before substituting.