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From: "Bill Sloman"
Subject: Re: How to construct PWM pure sine wave inverter ?
Date: Wed, 16 Oct 2002 01:05:17 +0200
Organization: Planet Internet
References: <firstname.lastname@example.org> <email@example.com>
NNTP-Posting-Date: 15 Oct 2002 23:05:15 GMT
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"Booboo" wrote in message
> >Suggestion: google for 'magical sine waves'
> I think he means a ~real~ sine wave.
A pulse-width modulated digital data stream - just ones and zeros - looks
exccedingly like a sine wave if low-pass filtered by a good filter.
The problem with Don Lancaster's magic sine waves - which are just very long
binary sequences - is that the high frequency noise is big and and you need
a multipole filter to get it down to acceptable proportions. Not a problem
with a fixed frequency source, but for a variable frequency source, the DDS
technique of driving a D/A converter from a phase accumulator via a look-up
table is to be preferred.
For power applications, where you really need PWM, Don Lancaster's magic
sine waves probably have too many switching edges to be acceptable - each
transition dumps a lump of energy into the switch and you need to ration the
number of transitions.
Bill Sloman, Nijmegen
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