170W Audio Power Amplifier
With LM4651 & LM4652
The combination of the LM4651 driver IC and the LM4652 power MOSFET Class D power amplifier IC provides a high efficiency amplifier solution, suitable for self-powered speakers, subwoofers and quality car boosters.
The LM 4651 is a fully integrated conventional pulse width modulator (PWM) driver, containing undervoltage, short circuit, overmodulation, and thermal shutdown protection circuitry. The IC features a standby function which shuts down the pulse width modulation, minimizing supply current.
The LM 4652 is a fully integrated H-bridge Power Mosfet IC in a TO220 power package. The IC has a built in temperature sensor to alert the LM4651 when the die temperature exceeds the threshold limit.
Used together, the LM4651 and LM4652 form a simple, compact, efficient, high quality power audio amplifier solution complete with protection, normally seen only in Class AB amplifiers.
The maximum efficiency of this circuit is 85% at 125W with a standby attenuation greater than 100dB. The THD at 10W, 4 ohms, 10 – 500Hz is max. 0.3%. The supply voltage can not exceed ± 22V.
For the best performance a suitable preamplifier is required. With the addition of a preamplifier the gain of the power stage can be greatly reduced to improve performance. The gain should be set to 10 V/V allowing for low gain on the Class D stage with a total system gain high enough to be a complete solution for line level sources.
The input filter used here does not noticeably increase THD performance but will help to maintain a flat frequency response as the Q of the output filter changes with load impedance.
Design notes, full specs and recommended PCB reference designs can be found here.
Do not attempt to build this amplifier as your first project! Class D high power amplifiers are expensive, difficult to build and a very small error during assembly can lead to total devastation of the power IC or other costly components.