class d amp power supply watts

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panos1

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Joined 2013
#1
hi...
i have a question about class d amps...
they have an efecincy of about 90%..
so with a 300watts psu i can take 270 watts of sound...
in order to take 270 watts i need 2x50 volt psu...(so 100 volt)..
a 300 watts psu can give about 3 amps at 100 volt...
but if wee calculate the amps that the amp will outpout we will find out that we need more amps..
the amp will outpout 33 volts.
so 33/4(4ohms load)=8.25 amps...
so haw the amp can outpout 270 watts out of 300 watts psu?
 
#3
A lot of manufacturers can get away with a much smaller PSU than the output suggests. Because of the crest factor in music you won't need 300W continuous, only a fraction of that. If you want to be prepared for everything (sine wave tests for example), you need to get a PSU of (Voltage^2)/(2*impedance).

In short, only taking efficiency into account and running a sine wave: yes 270W is the limit.
 
#4
thank you for the replies...what you mean that the amplifier can trade amps for volts?
can you explain it? 😉
i want to drive subwoofers with my amp so i don't think that i will be ok with smaller smps...
 
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#5
By "trading amps for volts" I mean that in a way, your amp works as a transformer, converting the 2 x 50 V 3 A from your power supply into 33 V 8.25 A into your speaker. What matters is the total power (as long as you have enough voltage swing). Even if the speaker requires 8.25 A, your amp will be able to supply it (as long as the power supply can supply at least 273W, and as long as the amp can provide the required 33 V).
 
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