| The switch-type (type D) audio power amplifier designed by the author uses the time-base circuit NE555 to drive the two-channel power amplifier TDA1521, which can output 30W × 2 power with an efficiency higher than 85% when powered by ± 16V. |
| The electrical principle is shown in the figure. The NE555 time-base IC is connected as a square wave oscillator with an oscillation frequency of 120 kHz and a duty cycle of 50%. When the audio signal is input by the ⑤ pin, the duty cycle of the output signal of the ③ pin will change linearly with the amplitude of the input audio signal. This signal is amplified by the power of TDA1521, and then the audio signal is restored by the filter circuit composed of L1 ~ L4 and C1 ~ C4. Fast recovery diodes D1 ~ D4 are used to protect TDA1521 from the damage of L1-L4 self-inducted potential. Because the ICs work in the switching state, they can output high power with high efficiency. |
| No audio signal is input during debugging. At this time, the voltage of the output terminal of TDA1521 should be 0V, otherwise the time-base circuit statically outputs an asymmetrical square wave, and the RP should be adjusted to correct it. Then the input signal speaker should sound. When the 1kHz audio signal is input and the output power is 30W × 2, the measured efficiency is more than 85%, and the harmonic distortion is less than 0.8%. The effect is unexpectedly ideal. |
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