Hey Guys,

I am familiar with LPF for high output power concepts but am unsure of what type of inductor to choose.

My application will need about 8A RMS and I have pasted a circuit I am referencing as this is my first audio venture.

While looking at the circuit, why is there a requirement to add those bypass caps and snubber caps on the output stage? I figured them unecessary considering the waveform is already being smoothed by the big inductive low pass?

Furthermore, why bother using a big inductive filter on the output stage when a speaker itself is basically just a massive inductor and resistor in series?

Any insight would be greatly appreciated.

Cheers

 

Hello,

You are looking st the class D amplifier.
This consists of a modulated PWM signal.
The inductor is there to "smoothen" the PWM pulses to the audio signal.

Greetings,
Bertus

 

Hello,

You are looking st the class D amplifier.
This consists of a modulated PWM signal.
The inductor is there to "smoothen" the PWM pulses to the audio signal.

Greetings,
Bertus

Hi Bertus,

yes I realize that, but if the speaker itself is a big inductor, one I assume even larger than 18uH shown here, that will have a smoothing effect anyways.

The only thing I can rationalize is to smooth the switching out as soon as possible for EMI etc.

Furthermore, if I go and throw that inductive low pass filter on the output stage prior to knowing the inductance of the speaker, how can I say I'm not filtering out more than I want to?

I.e. the LPF shown above has a bandwidth of about 30kHz as it is designed for 4 Ohm speakers. This is before considering the inductance of the speaker, so in reality, the bandwidth should be less?

 

I am not a pro in D amps, but I guess it is to prevent destroying of HF speakers, and maybe for stability reasons too.
But anyway, ask at http://diyaudio.com there sure are people who can explain it to the slightest details.