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-   -   Pre-clipping as a method of power regulation (http://www.diyaudio.com/forums/class-d/122287-pre-clipping-method-power-regulation.html)

bkoopman 1st May 2008 06:18 AM

Pre-clipping as a method of power regulation
 
Since most of my experience is in the 12V field, I'll center the idea there. I suppose this applies to any design, though.

For whatever reason, some designs regulate the power output of a class-D amplifier (doesn't apply to a/b). This is always done by regulating the secondary voltage, and running the output stage into saturation. Pre-clipping the output signal at some point would have roughly the same effect, and would greatly simplify power supply.

The output stage would have to be more robust, especially when the goal is to make full power into a range of output impedances. This cost, however, has to be paid anyway, be it in the power supply, or the output stage. I've done the math, it's definitely less efficient to regulate the secondary DC voltage than the output signal. Many of the problems associated with hard clipping are also eliminated.

I've finally found enough time to build a UcD for a car. I've built many different car PS in the past, even had a 1.5kW Weinberg at one time, but never had much luck with regulated supplies. At low frequencies, the output inductor is huge. At high frequencies, the leakage inductance of the xfmr eats your lunch. In either case, high line = low duty cycle = lots of loss everywhere = bad news. Just seems that running a simple chopper, and limiting the output swing is easy to implement, and can be adjusted on the fly faster than you can say compressor-limiter.

Any thoughts? I'll definitely post my progress here.


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