New Zetex down converter (DN 73)

[robk]

I threw together a down converter based on the Zetex design note 73, to drive a LuxIII. I was rather impressed with the results! No smoke, worked first time, pretty good efficiency, not bad regulation (appears to be voltage reg). I'll probably use it in a 4AA or 2-CR123 housing to drive a LuxIII. It's big, but it can be shrunk a bit, I wasn't trying to make it tiny - as it was a test of their circuit. The current output is slightly low as I used a 22 milliohm resistor instead of 20, cause that's what I had. Don't laugh at the solder blobs, I use a real fine tip iron but I still can't get used to these microscopic surface mount parts. Here's what I measured:
V input____A input____V output___A output
6.0________0.70_______4.0________0.942
5.5________0.71_______3.99_______0.891
5.0________0.77_______3.98_______0.879
4.5________0.78_______3.92_______0.834

At 6V, that's 89% if my figures are right. The inductor used was a DigiKey 308-1241-1-ND. (I finally found a family of power inductors at DigiKey that work!) Here's a photo of the test board and LuxIII (bin unknown - bare emitter from Elektrolumens)

The heat sink is one of the designs I have made locally, 2.25" thick AL, dia to fit Mag "D" bodies. I also make them flat for stars.
Just thought a few guys might like to see the results of Zetex's new 3W application note.
Rob

 

[PEU]

Great Rob,
good: you found the inductor! /ubbthreads/images/graemlins/smile.gif

bad: I just finished my digikey order yesterday and is flying to Buenos Aires already /ubbthreads/images/graemlins/frown.gif /ubbthreads/images/graemlins/banghead.gif

Cheers

 

[robk]

Pablito,
That always happens to me too. Just got in about $80 worth of assorted parts (not all flashlight related) and I forgot to order a couple of 4mHz crystals for an IR remote control project.
Anyway, these inductors are a little large for the typical round converters, but they are good for boards mounted in Mags. I got a few different values, the current rating on them is decent - the 22uH shown is rated 1.5A.
Rob

 

[koala]

The solder job looks super strength to me /ubbthreads/images/graemlins/wink.gif

Vince.

 

[robk]

Hi Vince!
I just want to make sure the parts don't fall off the copper /ubbthreads/images/graemlins/smile.gif
I gotta work on that, but those 0805 size resistors are incredibly small, even with real thin solder.
Rob

 

[PEU]

Robk:
I received today a sample kit from Wilco, rewording, I received a big box with 10 sample kits, almost 500 different inductors.

Still browsing the fisherman like acrilic boxes...

May be you want to order one also, they are completely free of charge / free shipping!!!

cheers

 

[snakebite]

looks like too many parts to bugwire into a tiny package
btw where did you get that diode /ubbthreads/images/graemlins/grin.gif
[ QUOTE ]
robk said:
I threw together a down converter based on the Zetex design note 73, to drive a LuxIII. I was rather impressed with the results! No smoke, worked first time, pretty good efficiency, not bad regulation (appears to be voltage reg). I'll probably use it in a 4AA or 2-CR123 housing to drive a LuxIII. It's big, but it can be shrunk a bit, I wasn't trying to make it tiny - as it was a test of their circuit. The current output is slightly low as I used a 22 milliohm resistor instead of 20, cause that's what I had. Don't laugh at the solder blobs, I use a real fine tip iron but I still can't get used to these microscopic surface mount parts. Here's what I measured:
V input____A input____V output___A output
6.0________0.70_______4.0________0.942
5.5________0.71_______3.99_______0.891
5.0________0.77_______3.98_______0.879
4.5________0.78_______3.92_______0.834

At 6V, that's 89% if my figures are right. The inductor used was a DigiKey 308-1241-1-ND. (I finally found a family of power inductors at DigiKey that work!) Here's a photo of the test board and LuxIII (bin unknown - bare emitter from Elektrolumens)

The heat sink is one of the designs I have made locally, 2.25" thick AL, dia to fit Mag "D" bodies. I also make them flat for stars.
Just thought a few guys might like to see the results of Zetex's new 3W application note.
Rob

[/ QUOTE ]

 

[robk]

PEU- Did you choose the individual samples, or did you get a ready-made kit, like "W" series?

Snakebite- Ah, you recognize your diode! Thanks for the parts, they came in handy!

Rob

 

[PEU]

I asked for smd inductors and they sent all the ones they have, not ten as I told you before, but six boxes of 12 compartments each with 5 inductors, total 360 inductors.
I sent the request via fax and they shipped the whole package and the catalog to Argentina.

I don't know their minimal order, but to test circuits having that range of inductors with the mH and mA VALUES is great. /ubbthreads/images/graemlins/smile.gif

Hope they send the package to you too.

 

[robk]

Well, I ran a runtime test of the Zetex circuit using ScopeView on a Radio Shack DMM. The power was 6 1800mAh NiMH cells, fully charged. The LED is an unknown bin emitter from Elektrolumens. I thought I'd get a bit more time from the NiMH cells, maybe they are weak or old. What is impressive is the almost flat current output to the LED until it drops out of regulation. Pretty good for a cheap Zetex circuit. The test setup was 6 1800mAh NiMH cells, freshly charged - I have no explanation for the "blip" in the first 15 minutes, except that I powered up the fan on the big celeron heatsink during that time. The LED was mounted on a "mag diameter" heatsink that was temporarily epoxied to a celeron heatsink. Sense resistor is .022 ohms (Zetex specs a .02). The meter's 20A range was used. The vertical lines represent 15 minutes, the current starts out at about 1.1A.

Here's the graph:

I will try it again with Alkaline cells just to see if the results are similar. All in all, it's pretty flat with a decent output after regulation stops (leaving you with a little light). Lets see... 1.75 hours @ 1A from 1800mA cells, not too shabby!

Rob

 

[HarryN]

Nice work. Can this setup work as high as 12 - 14 volts in ?

 

[robk]

Since I used 6.3VDC caps, and 1 is across the input, I never tested the circuit beyond 7.2V (6 AA NiMh cells), so I can't answer the question. I don't think it would tolerate 12V in, but I could be wrong. I have one in a "2D mag" with 7.2V that works very well. Sorry!
Rob

 

[HarryN]

Hi - Thanks for the info. If you ever decide to up the Vin ability to the 12 - 14 volt range - let me know - I would be interested. Thanks HarryN