40109 Quad Low-to-High Level Shifter

A CD40109 CMOS integrated circuit providing a quad low-to-high voltage level shifter. Shifts four logic signals from a lower supply voltage to a higher one, with separate supply pins for each side. Used to interface 3.3V logic to 5V or higher CMOS. Being 4000-series CMOS it runs on anything from 3 to 18 volts, which makes it far more flexible than 5V-only TTL logic and lets it work directly in battery and higher voltage circuits. It also draws almost no current when idle. The trade-off is speed: CMOS of this family is slower than 74HC logic, so it suits control, timing and teaching applications rather than fast data paths. Unused inputs must be tied to a supply rail, never left floating.