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Old 12-23-2012, 12:23 PM   #1
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Warning: non-dimmable LEDs

I've been replacing all of my interior lights with the 10-LED discs and, in may cases, homemade fixtures. I've also been touting an easy way to dim these LEDs--just a SPDT switch (on-off-on) and one resistor.

I bought these LEDs from three suppliers--SuperBrightLEDs, Bright Source, and Eversale. To my surprise, the Bright Source LED discs are not dimmable (and I remember vaguely seeing that on their web site). They look almost identical, with the LED arrangement on the front indistinguishable from other vendors' products. The only difference is that the pins on the LEDs are soldered indiviually to the disc on the non-dimmable version, while the others are soldered to a continuous pad.

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But the back side is slightly different. All I can surmise is that the non-dimmable version has a true current regulator and no series resistor, which allows them to operate at almost full brightness all the way down to 8 volts and with considerable brightness down to 6.8 volts. They also have a bit more luminance than the dimmable version.

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Not a big deal unless you're planning to have a bright/dim switch.

Zep
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Old 12-23-2012, 03:00 PM   #2
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Good info to have, Zep.

So far, all of our LEDs have been in places where on/off was all we wanted. But for our planned overhead light, dimmable will be a desirable option.
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Old 12-25-2012, 05:31 PM   #3
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More in-depth info on the LED discs than you ever wanted to know (except for BARTS, of course) ...

I received 12- and 15-LED discs yesterday. The 15-LED disc is similar to the non-dimmable 10-LED disc described above, same voltage regulator (the A61) and other components (also purchased from BrightSource, same as the non-dimmable 10-LED discs). The A61 is a non-adjustable voltage regulator that has an output of 3.3 volts and maximum current of 0.3 amps.

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The 12-LED disc is very simple, no regulator. Just a bridge rectifier so that it is polarity independent. The small value of the series resistors tells me that the LEDs on this disc are wired in series, which restricts the operating voltage to a smaller range.

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All these discs use the 505 SMD LED package. It turns out there are three LEDs inside. One some of the discs all of them are soldered onto the disc in parallel. On others the leads are individually soldered, so it's not possible to tell whether they are also parallel or in series (series would be more efficient).

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For those who want the real tech data, here are two schematics from application notes for the regulators (the 7150 is used on the 10-LED disc and is adjustable, with a current limit of 1.5A).

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My bottom line is that these are all great products and have currents that are pretty much in line with the number of LEDs and lumens. But if you want to be able to dim them, then only the 10-LED disc with the 7150 is really suitable (that would be the disc on the right in post #1 above).

Zep
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