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From: firstname.lastname@example.org (N. Thornton)
Subject: Re: How to make/solder a circuit fast?
Date: 25 Sep 2002 15:53:51 -0700
References: <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com>
NNTP-Posting-Date: 25 Sep 2002 22:53:51 GMT
firstname.lastname@example.org (The little lost angel) wrote in message
> On Wed, 25 Sep 2002 11:50:03 GMT, email@example.com (Bob Masta) wrote:
> The project involves loading a SMPS with a variable resistive load
> (after the non-response trying to get high power resistors, I'm most
> likely going with power mosfets).
That does surprise me. Many part suppliers sell resistance wire, that
should do the job nicely. Bulbs are suitable sometimes, but not for
your job as they're inductive to some extent. So use the R wire in a
non inductive pattern. Doubling it into a U shape prevents almost all
the inductance. Then running it back and forth, _not_ spirally, should
avoid any L.
If you have a choice of wire size, thin wires in parallel will be best
> The spec allows for as low as 50mV ripple and noise, so the scope has
> to be able to pick that up at 3.3V to 12V range. And it's defined as
> within the band of 10Hz to 20Mhz
> Plus the SMPS must remain stable under rapid load changing conditions
> up to 10Khz.
> I haven't figure out a way to
> reduce 13.2V to a range acceptable by the soundcard without killing
> any 50mV spikes I'm interested in catching.
A resistive divider? Add tiny caps across the series Rs to bring the
freq response to flat upto your 20MHz, ie to cancel out the effeect of
Another option is to use a capacitor. That'll give you the ac noise
component unreduced, without the 12v dc present. Add diodes to clamp
the signal to within a safe range, and a series R to limit i during
clamping action. Use a flat plate ceramic across the main capacitor,
as caps dont always behave well at 20MHz. Ceramic plate caps are non
inductive, they are not wound like most other types.
Will that do it?
Did your high current measuring work out btw?
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