Power supply voltage vs amperage in class D output

[Lawnboy]

This still confuses me just enough to ask, hypothetically, two switching power supplies, 24v 21a output or 36v 14a output, ~500w. Let’s say we have a 160w x 2 amplifier board rated to operate between say, 15v-40v. Let’s say we can tolerate 1% thd and the amp will do ~120wpc at this thd.

This is what I haven’t quite fully absorbed mentally. With a 24v/21a power supply, can this amplifier achieve 160wpc? How about the rated clean-ish 120wpc? Is there truly an overall limitation based on voltage input? Is the abundance of amps at 24v a moot point after some input voltage bottleneck? Is 36v necessary to hit the amps rated output?

There seems to be a formula that predicts this concept, voltage multiplied by 2 divided by resistance? Is it so, that the voltage outputted to the speaker can’t exceed the input voltage minus losses? Resistance looks to affect this maybe?

Let’s just say for fun that we have a 2x400 amplifier board. A power supply with 12 volts and unlimited amperage can only do a couple of watts and after that the amperage matters not?

 

[Lawnboy]

Oh, so if we’re voltage limited with abundant amperage, will the amp play clean up to the limits of the voltage input? If the amp is rated at 120wpc at 1% thd but the lower voltage equates to say 80wpc, is that 80w as clean at 24v as 40v?

 

[Nisbeth]

You can be both voltage-limited and current-limited (basic physics) and both limitations will result in clipping (= distortion). Which basically means that for a given power level out, you need your power supply to provide sufficient voltage and current even under load.

Theoretically (= meaning from a calculation perspective), if the amp can draw enough voltage and current from the PSU when it needs it, there are no difference between using a "good enough" PSU and a massively oversized one. Subjective listening impressions may be different of course

 

[ximikas]

Hi. I think all depends at first what voltage amplifier requires at required power output. Maybe it not needs these 40v or 36v if its bridged ,most d class chip amplifiers are single supply , therefore bridged . Also some capacitors in close to amplifier will help to supply peak current for short time , reducing distortions ,caused by clipping,, because of voltage sag under load. But not all psu allows external capacitors at output.

 

[Lawnboy]

I’m interested in learning the proper formula if the one I roughly used is incorrect. I’m interested in learning how this works in a broad sense but specifically, I’m trying to implement this board in a two channel 4 ohm application. I do have a 21a 24v mean well switching supply and would like to try to avoid purchasing another $100 36v supply. I will have a Dayton Audio KABD 2x50 board providing a dsp’d stereo line level output also. If I can get roughly 80wpc @4ohm of relatively clean power from the wondom I’d consider that good enough.

https://store.sure-electronics.com/product/AA-AB32361

 

[ximikas]

For ic amplifiers , output power is specified in datasheet, for modules it may be not so clearly declared. Also d class have its own nuances, like switching loses , inductor loses and so . But maybe manufacturer can answer . There exists formulas for class AB amplifiers output power estimation at given psu voltage ,but I don't know how accurate they are for D class.

 

[availlyrics]

For 4 Ohms loads- Lower voltage higher current is suitable. So- 24V / 21A (You can still connectn 8 Ohms loads but o/p power will be reduced
For 8 Ohms loads- Higher voltage lower current is suitable. So- 36V /14A (Thats testing the max limits of that Class D chip for 4 Ohms loads though)
Plus load limits are decided by the choice of o/p L C filter design