Class-D audio amplifier

Thread Starter

T.B.

Joined Jun 19, 2020
9
Hello,
I want to design a class-d amplifier using a LTC4449 n-mos gate driver on LTSpice. But there is a problem in output signal. It is not a perfect sinusoid. I realized that ,according to data sheet, the gate drivers output Bg is not at desired interval and also there is a cross conduction current issue. I tried using a Mosfet that has small input conductance but it didn't work.
If someone could give an advice, I will appreciate for


class-d-amp-circuit.PNGclass-d-amp-circuit-ts-pin.PNGclass-d-amp-circuit-bg-pin.PNG
class-d-amp-circuit-out.PNG
 

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DickCappels

Joined Aug 21, 2008
6,791
It is clipping. I reduce the amplitude of the sine wave to 4.5 volts and the output waveform looks fine.

In real life this would probably work better if you used a balanced (both a positive and a negative) power supply or capacitively coupled the output to the load so you don't waste a lot of power because of the DC offset in output waveform heating up the load resistance.

1594978041817.png
 

Thread Starter

T.B.

Joined Jun 19, 2020
9
It is clipping. I reduce the amplitude of the sine wave to 4.5 volts and the output waveform looks fine.

In real life this would probably work better if you used a balanced (both a positive and a negative) power supply or capacitively coupled the output to the load so you don't waste a lot of power because of the DC offset in output waveform heating up the load resistance.

View attachment 212341
Thanks for your reply. I didn't consider signal's amplitude. Is there any specific reason about this clipping ?
 

DickCappels

Joined Aug 21, 2008
6,791
The control circuit tries to make the output signal that goes beyond the the +20V power supply and below ground, and that's a problem because there is no voltage available to make the output go beyond those limits.

AC coupling the output signal would greatly increase the efficiency of the output stage.
 

Audioguru again

Joined Oct 21, 2019
2,387
Most class-D audio amplifier ICs use a single-polarity power supply like this one but they use "bridging" (2 amplifiers, one for each speaker wire), then the speaker has the same average DC voltage on each of its wires, and a series coupling capacitor is not needed, and the output power is almost 4 times higher.
 

TechWise

Joined Aug 24, 2018
143
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