74145 BCD to Decimal Decoder/driver IC PDIP-16
The 74145 is a 4-to-10 (BCD-to-decimal) decoder/driver implemented in Low-Power Schottky (LS) TTL. It decodes a 4-bit BCD input (A, B, C, D) into one active low output among ten (Y0–Y9); all outputs are held off for invalid BCD codes. The device integrates pairs of inverters and four-input NAND gates to implement full BCD decoding and uses high-breakdown N-PN output transistors (open-collector) so the outputs can be pulled up to external voltages (the HD74LS145 supports up to 15 V on the off-state outputs), making it suitable to interface directly to indicators, lamp loads or relays when used with appropriate pull-ups.
Because the outputs are open-collector, the HD74LS145 sinks current rather than sourcing; each output is designed for high low-side drive (sink capability up to 80 mA for heavy indicator/relay drive). Inputs are TTL-level compatible and include clamp diodes for termination/speed control. The device comes in common 16-pin packages (DIP and SOP) and is a drop-in LS replacement for classic 74LS145 parts used in numeric display and driver applications.
Features:
- Decodes 4-bit BCD to one-of-ten active-LOW outputs.
- Open-collector outputs for high-voltage pull-ups (off-state up to 15 V).
- High-breakdown N-PN output transistors designed for indicator/relay driving.
- All outputs remain off for invalid BCD inputs (prevents false outputs).
- Low-Power Schottky TTL process (TTL input compatibility, faster switching).
Specifications:
| Parameter | Symbol | Min | Typ | Max | Unit |
|---|---|---|---|---|---|
| Supply voltage (recommended operating): | VCC | — | 5.0 | — | V |
| Off-state output voltage (allowed pull-up): | VO(off) | — | — | 15 | V |
| Output low sink current (per output, max): | IOL (max) | — | — | 80 | mA |
| Output low voltage @ IOL = 12 mA: | VOL | — | — | 0.4 | V |
| Output low voltage @ IOL = 24 mA: | VOL | — | — | 0.5 | V |
| Output low voltage @ IOL = 80 mA: | VOL | — | — | 3.0 | V |
| Off-state output current @ 15 V: | IO(off) | — | — | 250 | µA |
| Input VIH / VIL (TTL levels): | — | 2.0 | — | 0.8 | V |
| Supply current (outputs open): | ICC | — | 7 | 13 | mA |
| propagation delay: | — | — | — | ~50 | ns |
Pinout:
| Pin | Name | Description |
|---|---|---|
| 1 | Y0 | Decimal output 0 (active LOW, open-collector) |
| 2 | Y1 | Decimal output 1 |
| 3 | Y2 | Decimal output 2 |
| 4 | Y3 | Decimal output 3 |
| 5 | Y4 | Decimal output 4 |
| 6 | Y5 | Decimal output 5 |
| 7 | Y6 | Decimal output 6 |
| 8 | GND | Ground |
| 9 | Y7 | Decimal output 7 |
| 10 | Y8 | Decimal output 8 |
| 11 | Y9 | Decimal output 9 |
| 12 | D | BCD input D (MSB) |
| 13 | C | BCD input C |
| 14 | B | BCD input B |
| 15 | A | BCD input A (LSB) |
| 16 | VCC | +5V supply |
Applications:
- Driving 10-digit indicator lamps or vacuum/filament indicators.
- Driving relay coils or other loads that require a low-side switch (with appropriate pull-ups and flyback protection).
- Numerical display multiplexing and legacy display drivers.
- Open-collector logic interfacing where one-of-ten decoding is required (industrial counters, scoreboards, selectors).
Packages:
- 1x 74145 BCD to Decimal Decoder 5V 7mA IC PDIP-16.
