From: "Christopher R. Carlen"
Subject: Re: 87% All that vector calculus paid off
Date: Mon, 23 Dec 2002 09:13:19 -0800
Organization: Sandia National Laboratories, Albuquerque, NM USA
References: <firstname.lastname@example.org> <email@example.com>
NNTP-Posting-Date: Mon, 23 Dec 2002 16:11:48 +0000 (UTC)
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.1) Gecko/20020826
X-Accept-Language: en-us, en
Tony Williams wrote:
> Nothing to do with the magnetics Chris. The guesses are
> straight off your input/output figures above.
> 0.315A at 40% duty cycle gives a 0.8A mean current during
> the ON-time. For a triangular current, Ipk= 1.6A.
> 150KHz, 40%, is an ON-time of 2.7uS.
> V= LdI/dT. 45V = L*1.6A/2.7uS gives L= 76uH.
> Or from another direction.... P-out is 12W, and guess
> that there is another 1W lost on the Sec side (and in
> the core). P-in to the core is 13W. 13/150KHz = 87uJ.
> At 1.6A, 0.5*L*I-squared gives L = 68uH.
> A useful WAG to do because it points to scoping the
> ON-current as an early thing to do.... verify that
> apparent 1.6A, check that it is reasonably triangular
> (and not curling up as the core saturates), etc.
Indeed you are quite right. I am lacking some decent current sense
resistors. I'll be in a better position to make these measurements once
I get some of those. Nor did I take pains to cross check my numbers in
a few different ways. You see, on the weekend, it's all for fun! Sure
beats TV, don't you think?
I think the Al is measured at small signal levels, and at some
relatively low f like 25kHz, so that at higher frequencies as the
permeability decreases, it takes down the inductance, and also the
inductance tapers off a bit with high flux levels. So all of this isn't
Maybe tonight I can check the current with a 1 ohm resistor, which will
disturb the operating parameters a little bit but not too much, and see
what it looks like, before I go out to the movies with the wife.
Maybe I can have some fun and blame her for the inductance being wrong,
after all, she wound it :-D
Thanks for the input as always.
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA