From: "Fritz Schlunder"
Subject: Re: 87% All that vector calculus paid off
Date: Mon, 23 Dec 2002 08:06:49 -0700
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
X-Comments: This message was posted through Newsfeeds.com
X-Comments2: IMPORTANT: Newsfeeds.com does not condone, nor support, spam or any illegal or copyrighted postings.
X-Comments3: IMPORTANT: Under NO circumstances will postings containing illegal or copyrighted material through this service be tolerated!!
X-Report: Please report illegal or inappropriate use to
X-Abuse-Info: Please be sure to forward a copy of ALL headers, INCLUDING the body (DO NOT SEND ATTACHMENTS)
Organization: Newsfeeds.com http://www.newsfeeds.com 80,000+ UNCENSORED Newsgroups.
> When I adjust the duty%, and let's say there are three ring spikes
> present, and say I am increasing the duty% by hand. I don't see the
> output voltage changing proportionally to the duty%. Instead, the
> output voltage changes slightly, then all of the sudden it lurches
> upward as one of the ring spikes disappears.
The output voltage should be directly proportional to the duty ratio.
Suppose we intially run at 10% duty and we double it to 20%. This means the
on time is twice as long per cycle, so the current in the inductor will ramp
up to twice the original value. Since the energy in each packet is 0.5LI^2,
this means the output power should quadruple (assuming efficiency didn't
change). Since power in a resistive load is V^2/R, this means the output
voltage should have exactly doubled.
Are you measuing the output voltage with a DMM? In my experience DMMs (even
relatively expensive ones) are suprisingly often confused when the try to
measure a DC voltage with a bunch of high frequency goodies riding on top
(in your case switching noise and ripple voltage, especially since you are
using such a small output filter capacitor, and no additional LC filter on
the output of the output). Sometimes they seem pretty accurate, other times
a little off, and sometimes totally blatently off (sometimes fluctuating and
sometimes negative, etc.). I suspect the change in noise characteristics
associated with one less ring are causing havok with your DMM. How does the
output voltage change when you monitor the output voltage with your o-scope
-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 80,000 Newsgroups - 16 Different Servers! =-----