SMPS Requeriment for Class-D

[-_nando-_]

Hello,

I'd like to know what are the power supply requeriments for a R.M.S. rated Class-D amp.

For example, for a 90% efficient 100W R.M.S. amp, how many watts should my SMPS deliever?

Looks obvious that it would be 100W + 10%, but as I know, music will never, ever drain this much power.

I've been sucessfully using a 360W R.M.S. amp witha 240W SMPS!

I'd like to have your opinion and see some calculations

Thanks!

[wg_ski]

I seems to be common industry practice to size the power supply for current demand at 1/8 power with pink noise at nominal (not minimum) load impedance. That's for any amp regardless of class. High end professional stuff (Labgruppen, Crest, Powerlight) is designed with a bigger supply, but not the entry-level stuff. For home use you don't need much more, but the amp will have *better bass* if the supply can put out full peak current (Vcc divided by minimum RL) for at least the short term without going into a current limit mode. For larger amps, that can be a tall order.

[ssanmor]

It all depends on the kind of music you listen to, the long term power required and how tolerant your PSU is to overloads, but for serious equipment I wouldn't recommend less than the total power you require, (1000W-continuous-capable PSU for a 2x500Wrms amplifier, for example, assuming that it is Class-D), in order to be on the safe side and have lots of power reserve. You can hear lots of arguments trying to justify less, but that is simply skimping, with a detrimental effect on reliability and sound quality.

[-_nando-_]

Yeah, it's for professional use.

Actually, it will have three amplifiers of 700W R.M.S. @ 8Ohms, two driving two woofers (one for each) and another one sub-utilized (no need for 700W, but it's just easier to use the same amp) for the compression driver.

I'm thinking of two 700W continuous power supply's, one for +V and another for -V. Amplifiers will be fullbridge, so no concern about pumping effect!

Am I being exaggerated?

Best Regards!

[Pafi]

Since music signal is not constant, you shouldn't determine continous output, but peak power, and average powers for different duration. Peak power consumption can be 3-4 times more then rated power, but average power is fraction of that.

Some PSU can be overloaded very much for a short time, some of them limit their current if nominal power is exceeded, some of them shut down (etc...). You have to know what your PSU does under overload condition.

[Nisbeth]

There's a couple of slides about this topic in Bruno Putzey's electronics presentation (find it on the hypex website). IIRC it's something like: PSU current limit of twice the max peak current across the load and: PSU continous power (thermally limited) of between 1/3th and 1/8th of the max power consumption (= full output power / efficiency at full output). 1/8th power is typically enough for consumer applications whereas 1/3th would be the spec for PA amps.
Note: I am going from memory so check these numbers for yourself

/U.