74HCT4075 Triple 3-input OR (CMOS, TTL inputs) gate
The 74HCT4075 holds three independent 3-input OR gates. Each output is high when any of its three inputs is high. There is no 3-input OR in the 74LS family, so this CMOS part is the one to reach for — the HCT version reads TTL levels and takes a 74LS output directly, which a plain 74HC4075 may not. Where only TTL parts are allowed, two gates of a 74LS32 make the same function.
74HCT4075 pinout
Top view of the 14-pin DIP package. Pin 1 is at the bottom left, beside the notch, and the numbers run anticlockwise. Power is on pin 14 (VCC, +5 V) and pin 7 (GND).
| Pin | Name | Type | What it is |
|---|---|---|---|
| 1 | 2A | Input | Input of gate 2 |
| 2 | 2B | Input | Input of gate 2 |
| 3 | 1A | Input | Input of gate 1 |
| 4 | 1B | Input | Input of gate 1 |
| 5 | 1C | Input | Input of gate 1 |
| 6 | 1Y | Output | Totem-pole output |
| 7 | GND | Ground | 0 V |
| 8 | 2C | Input | Input of gate 2 |
| 9 | 2Y | Output | Totem-pole output |
| 10 | 3Y | Output | Totem-pole output |
| 11 | 3A | Input | Input of gate 3 |
| 12 | 3B | Input | Input of gate 3 |
| 13 | 3C | Input | Input of gate 3 |
| 14 | VCC | Power | +5 V supply |
74HCT4075 truth table
| A | B | C | Y |
|---|---|---|---|
| 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 1 |
| 0 | 1 | 0 | 1 |
| 0 | 1 | 1 | 1 |
| 1 | 0 | 0 | 1 |
| 1 | 0 | 1 | 1 |
| 1 | 1 | 0 | 1 |
| 1 | 1 | 1 | 1 |
What the 74HCT4075 is used for
- Three-term sums in a sum of products
- Combining three enable or error lines into one
CMOS, not TTL: there is no TTL 3-input OR, so this is the part to buy when a design wants one. The HCT version reads TTL levels, so it takes a 74LS output directly (a plain 74HC part may not see a 74LS high as a 1). Outputs drive about 4 mA either way; an input draws next to nothing. A lab that allows only TTL parts will want two 74LS32 gates instead.
Electrical summary
| Package | 14-pin DIP |
| Supply voltage | 5 V (4.75 V to 5.25 V) |
| Supply current, typical | 0.002 mA |
| Output type | Totem-pole — drives both high and low |
| Output current, low | sinks up to 4 mA |
| Output current, high | sources up to 4 mA |
| Input current, low | 0.001 mA out of each input held low |
| Fan-out | one output can drive about 10 LS inputs |
Typical figures for quick reference when planning a board. Check the manufacturer's datasheet for limits and timing before committing a design.
Try the 74HCT4075 on a breadboard
The Breadboard Simulator has the 74HCT4075 in its parts library: seat it on a virtual breadboard, wire it, power the board and probe the pins before you build the real thing.