Author Topic: Insides of a Malibu 7w LED Landscape light  (Read 5999 times)

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Offline slburris

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Insides of a Malibu 7w LED Landscape light
« on: September 06, 2010, 10:42:50 pm »
As you probably know from other threads, I'm a big fan of LED lighting.  Today
I picked up a 7w LED landscape light from Home Depot.

Looking down the business end, there are clearly 3 LEDs of some sort.  I easily
unscrewed the metal ring holding everything together.  The cover is a piece of glass
with a rubber gasket to keep the rain out.

Once the cover is off, we see what looks like a PCB with 3 LEDs on it and a plastic
focusing lens.  A 1000uf 25v electrolytic peeks out from under the board.

Taking the 4 screws out, we see the LED board is hiding a second PCB.  The LED
board has a metal back, but only seems to heatsink to the enclosure at the edges.
Will this cool things adequately?  Who knows?

Next, lets look at the inner PCB.  Clearly a discrete full wave bridge rectifier design.
This is important in landscape lighting as you have no idea what the polarity of
the power line is.  As a bonus, this circuit will work off of low voltage AC as well.
The diodes are all SS12's, 1amp Schottky rectifiers.

Note that there is an inductor to the right side of the PCB.  I would have put
heat shrink on the inductor legs -- they are awfully close to the case screw and
the circuit output.

The small integrated circuit is an MT7201  from Maxic Technology.  This is a
1 amp constant current LED buck driver:

http://www.maxictech.com/en/UploadFiles/MT7201_rev1.1_EN.pdf

This light is specified to run as 12 volts only, however the MT7201 operates down
to 7 volts.  Given that the Schottky rectifiers drop less than a volt apiece, this
light should operate down to something less than 9v, which means it should work
just fine on long cable runs.

The MT7201 can run at up to 30v, but this design has a 25v electrolytic and
Schottky diodes with only a 20v PIV rating, so this light cannot be fed more
than 20v, and that leaves zero safety margin.  An enterprising user could replace
the diodes and the capacitor with higher rated components, then run at a higher
voltage, although I'm not sure why you would want to.

I'll have to wait until tonight to judge the light output compared to my 3 watt
Portfolio floodlights from Lowe's.

High resolution photos attached - click only if you want to see the glint of
individual solder joints!

Scott
 


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