Class D/T current draw?

[David_Web]

With a class AB producing 8V RMS into a 8ohm load you'd see a current draw from the supply being 1A (RMS). Even if the supply is at 32V as the rest is converted to heat in the transistor.

Now to my question. What happens with a Class D or T?
Assuming little loss in the amp itself, does it present a 0.25A load to a 32V PSU or would the PSU still see it as 1A?
Or is it an extremely ugly load drawing 1A then nothing then 1A at a very fast rate?

[Boscoe]

You will still have your 1Arms although peaks will be higher before filtering. The voltage is just 'divided' more efficiently by PWM instead of a linear approach.

[nigelwright7557]

Class AB is around 60% efficient.
Class D is around 90%.

[Boscoe]

But will still draw the same current....?

[nigelwright7557]

Originally Posted by Boscoe

But will still draw the same current....?

No the class ab will draw more current of which 40% will be lost in the heatsink as heat.

[Boscoe]

Originally Posted by nigelwright7557

No the class ab will draw more current of which 40% will be lost in the heatsink as heat.

Are you sure? It's the voltage that's causing this, a class D amplifier is not more efficient because it draws less current it's because it's regulates the output voltage more efficiently look at a PWM and linear voltage regulators both will draw the same current given the same output the linear has lost the excess voltage as heat whereas the PWM is just on for less amount of time then this is averaged out.

I have never come across larger PSUs for linear amps, They draw the same current use the same voltage just regulate it different ways.

[David_Web]

After a bit of thought I made up a simple PWM circuit ltspice.
With a filter cap it does seem to draw 0.25A (at 32V) while dumping 1A (at 8V) into the 8ohm load.


Does this observation make sense?
And does this mean that a higher voltage, lower current supply can be used with the same result as a lower voltage, higher current supply?
Given you don't clip to rail with the lower supply or burn something with the higher.