Step-down switching regulator advice ?

I need a popular (easily available), low cost step-down switching regulator
suitable for an input voltage of up to ~ 18V that will deliver ~ 1A @11V with
Vin ideally as low as 11.25V.

What would you recommend ? I'm not at all familiar with the offerings here.

Graham

 

http://tinyurl.com/33nky7

 

LM2575's switchers are pretty popular.
Second sourced by ON Semi, and possibly others.

Not sure about the 0.25V drop though.
And you'd need the adjustable one - requires 2 external programming
resistors.

 

Pricy ! That's around $10.

Maybe I wasn't clear. I don't need a module, just a controller chip.

Graham

 

OK, got the data.

An adjustable one is just fine.

The low voltage drop is important to me. I suppose an alternative might be a
buck-boost circuit. This would actually be even better suited to my needs. In which
case my spec would be 1A @ 12.6V output with 11-18V in.

Graham

 

Keep waiting, the US dollar has a lot more sinking to do.

 

Let's try electronics design with Google.

In a panel at the right of your post in Google Groups
is a "related pages" panel, where I see National
Semi's LM2587 is recommended. Two clicks gets us to
http://www.national.com/pf/LM/LM2587.html where we
see that a simple flyback-transformer converter might
work. In a panel to the right we see NSC's WEBENCH®
tool to test the thought. OK, we enter 10 to 20V in,
12.6V out, 1.5A max, and press START YOUR DESIGN.

Oops, they want me to log on. Sigh. OK, press START
again, and whammo, there it is -- our design, pretty
routine, except a custom transformer is called out.
But it's an easy one, with Ns/Np = 0.78, Lp = 23.4uH,
and Lell no more than 0.47uH, or less than 2% of Lp,
which is pretty easy to wind. They specify Rp under
35 milliohms, which should help pin down the bobbin's
winding area, and a ferrite-core size. They say the
LM2587 will dissipate 3.5 watts, so we'll need a heat
sink clip on the TO-220 tab.

Hmm, DigiKey wants $8.32 just for an LM2587 TO-220-5
IC. Maybe the $10 TI module isn't so bad after all.

 

Winfield Hill a écrit :

Hmmm, maybe it's time to plan for a new chapter in AOE that'll teach
back of the envelop mouse dragging and clicking...
Then you can include there some nice lists of jellybean URLs for design
websites.

 

Every time I tried that I got a message that my design was not possible.
All are in mass production now ...

3.5W at 11W out? Ouch.

Double-Ouch. I usually do SEPICs with the LM3478. About a buck in
quantities and that external FET ain't expensive either. If it has to be
dirt cheap I'll use a Schmitt inverter. And it usually has to be dirt cheap.

It's like TV dinners. Either they are bland or expensive. When you whip
up your own from scratch it costs less and tastes better.

 

Which then quit working during the first year of print...

But you brought up a good point. Some links could be useful for younger
engineers, especially to university sites that remain intact like this one:

http://emclab.umr.edu/pcbtlc2/index.html

 

On Sun, 11 Nov 2007 17:07:18 GMT, in sci.electronics.design Joerg

snip thinking guy's stuff

I've never ever had a TV dinner

this is quite a nice site
http://www.lovefoodhatewaste.com/recipes/list?food=101


Martin

 

Same here. Even on lengthy biz trips where they rented me an apartment I
cooked my meals. The farthest I went with pre-prepped stuff was a
take-and-bake pizza.

We use all our left-overs, trying never to throw food away.

 

My best ever work trip, as a video guy, was in Kuala Lumpar, in the
hilton for a month (Shyte), within 5 minutes walk, 35C, 95% RH, there
where about 20 stalls of local food, 100K Scoville units and more, a
full meal + beers for the price of a coke in the Hilton.

I'm more into flavour these days than WMD


Martin

 

Waist mangling deserts? ;-)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

Or this one:

http://schmidt-walter.eit.h-da.de/smps_e/smps_e.html

robert

 

Hey, great site! Thank you, bookmarked it.

 

Likewise. Very handy indeed.

Graham

 

great site, I'd forgotten about it.....

Looking at
http://schmidt-walter.eit.h-da.de/smps_e/spw_smps_e.html

Just wondering why the secondary has the phase dot to ground.

Any ideas?


Martin

 

When the fet switches off, the drain shoots posive.
That is the non-dot side of the primary.
So the non-dot side of the secondary also shoots positive,
opening the diode and charging the cap.
You could of course change BOTH winding connections to get the same effect

 

Sheesh, so obvious, thanks


Martin