Power factor correction and audio apps

Thread Starter

leo0001

Joined Sep 30, 2018
79
Hi,

I would like to do a Class D amplifier, that means that there is a low pass filter at the input of the speaker. And I would like to have a good sound qualitiy, even if it is a Class D amplifier. The power output would be about 80 W (something like that). The source is an AC voltage source (50 Hz frequency). I would like to know if it is really important to do a PFC at the input in order to minimize electromagnetic interference and keep a gound sound quality. I mean that some interferences (without PFC) could interfere with the audio signal. (I cannot put the filter next to the speaker in order to limit the audio signal area). Even if I put the filter next to my speaker, the EMI interference will have a peak spike @ 100 Hz and I won't be able to filter it...

Nevertheless, I won't be able to "hide" the radiated EMI from the switching frequency of the PFC. So i will replace the problem by another.

What do you think ?

Thanks a lot :D

Léo
 
Last edited:

Papabravo

Joined Feb 24, 2006
12,405
Hi,

I would like to do a Class D amplifier, that means that there is a low pass filter at the input of the speaker. And I would like to have a good sound qualitiy, even if it is a Class D amplifier. The power output would be about 80 W (something like that). The source is an AC voltage source. I would like to know if it is really important to do a PFC at the input in order to minimize electromagnetic interference and keep a gound sound quality. I mean that some interferences (without PFC) could interfere with the audio signal. (I cannot put the filter next to the speaker in order to limit the audio signal area)

Thanks a lot :D

Léo
That's a new one. AFAIK PFC has nothing to do with audio quality. Where did this quaint notion come from?
 

Thread Starter

leo0001

Joined Sep 30, 2018
79
Hi,

Thanks for your answer ;) Could you tell me why a PFC is useless in audio apps ? Radiated EMI @ 100 Hz cannot be find on the audio signal ?
 

DickCappels

Joined Aug 21, 2008
5,882
In a well-designed amplifier there is no significant coupling of the AC signal on the power mains into the audio circuit. Therefore, the presence of an PFC is irrelevant to performance.
 

MrChips

Joined Oct 2, 2009
19,275
Power Factor less than 1 occurs when there is a reactive load. In this situation, the current through the load is not exactly in phase with the applied voltage. For filters, a phase difference of 45° instead of the desired 0° occurs at the cross-over frequency.

In a Class-D amplifier, the cross-over frequency is selected to be higher than the audio frequency band of 20-20kHz. Hence it is chosen remove the Class-D clock signal and will have very little effect on the quality of the audio signal
 

Thread Starter

leo0001

Joined Sep 30, 2018
79
Hi, thank you for all your replies.

Ok I will not do a PFC, it will be simpler for me :D

DickCappels, What do you mean by a "well designed amplifier" ? I can understand by using EMI filter you can reduce conducted EMI but I cannot understand that you can reduce radiated EMI unless by using shield and reduce sensitive area. I want to understand :D

MrChips, the speaker load (inductor) is a reactive load, am i wrong ? The radiated EMI would be @ 100 Hz without a PFC (full bridge rectifier) which is between 20 Hz and 20 KHz. So the filter won't be able to filter it.

Thanks,

Léo
 

Papabravo

Joined Feb 24, 2006
12,405
In order for an electronic system to radiate effectively it must have a suitable antenna, and that antenna needs to be matched to the source. Tell me what the wavelength of 100 Hz. is and I can opine on effective antennas.
 
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