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Class D: power supply regulated or not?
Class D: power supply regulated or not?
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Old 26th October 2009, 12:04 PM   #1
matherp is offline matherp  United Kingdom
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Default Class D: power supply regulated or not?

Hi all

Apologies if this has been answered but couldn't find anything in the searches.

I'm building a power supply for one of the Sure 2 * 100W class D (T) amps. I've got a nice 300VA toroidal transformer but don't know whether to regulate the output with a pair of LM338Ks or just smooth it.

Basic circuit is full wave rectification; thermistor surge protection; 0.1ohm, 2 * 22000uF capacitor RC smoothing,

Then the question is whether to regulate the output using the LM338s or just put another big capacitor after the RC filter.

What are the pros and cons?


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Old 26th October 2009, 02:39 PM   #2
Sch3mat1c is offline Sch3mat1c  United States
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Does it not seem strange to you to suggest linear regulation for a class D amplifier? Why not cut out class D altogether and use an LM3886? Or cut out linear altogether and use buck regulator(s)? Or cut both out and use a better amp, one with high PSRR?

What is the PSRR spec on the amp? If it's 80dB or more, leave it be.

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Old 27th October 2009, 12:16 AM   #3
star882 is offline star882  United States
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What does the datasheet say? The logic will almost always need regulated power, but the power stages might be able to not use regulation. If it's SE, it most likely would require regulation as it depends on a regulated voltage for the Vcc/2 to remain stable. BTL can sometimes do without regulation, however.

It's silly to not use regulation nowadays, however. Just build a buck converter. It might even be possible to use dynamic supply voltage to increase resolution at low volume settings.
"Fully on MOSFET = closed switch, Fully off MOSFET = open switch, Half on MOSFET = poor imitation of Tiffany Yep." - also applies to IGBTs!
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