Hi-Fi 38W Class D amplifier circuit

This class D amplifier uses the high-fidelity two-channel class D amplifier control integrated circuit LX1710 produced by MICrosEMI, and an external power field effect tube to form a BTL amplification. It can obtain 38W output power on a 2Ω load and the efficiency is about 84%.

The basic parameters of LXl710 are as follows: power supply voltage 7V-15V, output power per channel 25W (V=15V, 4Ω). At this time, THD+N=0.1, frequency response 10Hz~22kHz; when f=1kHz, output power 1W, THD+N=0.05; signal-to-noise ratio 81dB; switching frequency 335kHz; standby current 25μA.

LXl710 is equipped with noise filtering circuit, overcurrent protection circuit when load is short-circuited and static current reduction circuit, etc. The SLEEP terminal is in standby state at 0V and in working state at 2V.

The whole circuit is shown in the figure, with relatively few peripheral components.

The feedback signal is connected to the feedback amplifier in the chip through R3 and R4. Since the load impedance has a great influence on the characteristics of the output LC filter, the parameters of L and C should be adjusted according to the load. The parameters shown in the figure are when the load is 4Q. The actual test frequency response range is 5Hz~24.5kHz, -3dB.

This machine selects a low-threshold power field-effect tube. The Vcs of the tube model shown in the figure is 1.6V, and the on-resistance Rds (0n) = 0.019Ω.