[Blabber] Switching long strings of LEDs

Guan Yang guan at yang.dk
Sat Dec 31 20:12:30 UTC 2016


If you are looking for a cheap and easy module, you are probably limited
to what's on eBay or Aliexpress.

Digi-Key has a few expensive board mount modules, but they all require
at least 15.4V or 24V input:

https://www.digikey.com/products/en/power-supplies-board-mount/dc-dc-converters/922?k=&pkeyword=&pv1120=382&pv1120=554&pv1120=389&FV=15c0002%2Cffe0039a%2C17d400de%2C17d40125%2C17d40126%2C17d40127%2C17d40131%2C17d40148&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

(These are all constant voltage supplies so you'd need some kind of
constant current circuit like a (large) resistor or a proper LED
driver.)

You have more options if you're willing to do a custom board. For
example, there's this IC, which is a full LED driver, not just boost
converter:

http://cds.linear.com/docs/en/datasheet/3956f.pdf

They do have a $175 demo board but it's probably bulky, and it is fixed
to 375 mA.

And even more options for "normal" constant voltage boost converters
that are not designed as LED drivers.

On Fri, Dec 30, 2016, at 15:05, Rob Johnson wrote:
> Looking for some advice:
> 
> I'm helping a friend with a project, she's trying to control "strings" of
> LEDs, i.e. a chain of 10-25 LEDs in series. Control == switch them on and
> off sometimes, don't even need to do pwm.
> 
> Because the current requirement for a string is pretty low (30ma, or so),
> I'm thinking of playing around with a MAX6922 VFD tube driver, as this is
> serially controllable, and can output 76v*40ma per pin.
> 
> I'm now stuck trying to find a reasonable Boost converter that's small,
> and
> can get me 60-75v from 12v (preferably 9v or 5v). Ebay has a few things
> that can get me 40v
> <http://www.ebay.com/itm/DC-DC-3V-35V-To-4V-40V-Step-Up-Power-Supply-Module-Adjustable-Boost-Converter-/122271129659?tfrom=121419164360&tpos=right&ttype=coupon&talgo=undefined&autorefresh=true>,
> but I can't find anything better. A 40v source will be ok, since that can
> power 13-20 LEDs but if I can get more volts, I can get a better result,
> and it would be a shame not to.
> 
> TL;DR
> Where can I get a small boost converter that will give me 60-75v @ 1amp,
> or
> even less (I can probably make 1/4amp work)?
> 
> Happy new year,
> -Rob J
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