The LM1875 is a 20W audio power amplifier produced by National Semiconductor. It is suitable for consumer electronics products such as high-fidelity audio and power amplifiers. The product adopts a monolithic design, with large output power, low distortion, wide bandwidth, large output voltage swing, high current capacity, and wide supply range.
The LM1875 is a monolithic power amplifier offering very low distortion and high‑quality performance for consumer audio applications. It delivers 20 W into a 4 Ω or 8 Ω load on +25 V supplies and can exceed 30 W with an 8 Ω load at +30 V. The device includes internal current limiting and thermal shutdown for overload protection.
Key features include up to 30 W output power, THD of 0.015 % at 1 kHz, a wide supply range of 16 V‑60 V, high current capability of 4 A, 90 dB gain, 70 kHz power bandwidth, and a TO‑220 plastic package. Application hints cover PCB layout, stability, distortion control, thermal management, and recommended heat‑sink specifications.
| Maximum Output Power | Up to 30 W |
|---|---|
| THD (1 kHz, 20 W) | 0.015 % |
| Supply Voltage Range | 16 V‑60 V |
| High Current Capability | 4 A |
| Open‑Loop Gain | 90 dB |
| Power Bandwidth | 70 kHz |
| Ripple Rejection | 94 dB |
| Package | TO‑220 (plastic) |
It shuts down when the die reaches 170 °C and restarts when the temperature falls to about 145 °C, with a secondary shutdown at 150 °C if the rise continues.
The total junction‑to‑ambient thermal resistance must be less than 4.2 °C/W; with a lubricated mica interface this means the heat sink itself must be under about 0.6 °C/W.