Subject: Re: homebrew flyback transformer?
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Date: Tue, 08 Oct 2002 04:59:06 GMT
NNTP-Posting-Date: Tue, 08 Oct 2002 00:59:06 EDT
It's a litle bit more complicated.
Firstly, the inductance of an inductor is proportional with the square of
the number of turns, hence Ls/Lp=(Ns/Np)^2.
Second, I guess a toroid is not exactly what you need for a fly back, if the
configuration is really a fly back. The fly back (AKA boost) needs an air
gap in order to prevent the core saturation. Power levels involved are
important too. I would suggest you to read the Switch Mode Power Supply
design manual that you can find in Philips web site.
But why would a car battery go down to 11V? I thought it is 13.8V nominal,
and if the engine is running, the voltage could go up to 14.4V.
Also, do not neglect the insulation. It's easier to provide good insulation
on a transformer bobin, rather than on a toroid.
"Larry Gagnon" wrote in message
> I want to construct a power supply with the characteristics of
> 11-15vdc input, 12vdc @ 2.5A output (to power a small handheld
> computer in a vehicle). I have elected a design from National
> Semiconductors website: a flyback switcher PS based around the
> LM2587-12V switcher regulator. Other suggestions would be welcome!
> However, the flyback transformer required is "custom". I want to try
> to make it with toroids and magnet wire, of which I have plenty of
> variety, and I have a inductance meter. I have successfully made
> simple inductors this way in the past but this transformer has a
> I am a bit of a newbie with switchers. My question is : the design
> states the primary should be 35uH and then is says "Ns1 ratio" = 0.67
> or "Ns1toNp" = 0.67. I assume this means the secondary inductance
> ratio is 0.67 to the primary, i.e. 35*.67= 23uH??
> How reasonable is it to attempt to construct this transformer myself?
> Any comments or suggestions would be greatly appreciated. Thanks.
> Larry Gagnon
> to send direct email remove "fake" from address