Re: Driving large numbers of LEDs

On Thu, 15 May 2008 15:35:33 +0000, Guy Macon
<http://www.guymacon.com/> wrote:




I have a new client with an interesting product. They are driving
large quantities of LEDs (in the hundreds, with future products to
be in the thousands) in banks of red, blue, and green (with, of
course, different voltage/current requirements for different
colors). They want be able to dim each color using a microcontroller
-- PWM is OK as long as the human eye doesn't see any flicker.
Maximum efficiency is important: they want it to run cool and to
save energy. They are looking at a first run of 100 units to
test the market.

How would you go about meeting these requirements? An off-the-shelf
constant-current power supply and some uC-controlled switching
transistors is the first thing to come to mind for such small unit
quantities, assuming that I can find a power supply that is happy
having the load go from zero to max and back every few milliseconds.
Anyone have any better ideas?

How about three cheap (MeanWell are good) constant-voltage offline
switchers? LEDs aren't zero-impedance loads (some people run them
constant-voltage!) so aren't all that pickey. You could add a
current-sense resistor somewhere in each bank and have a uP measure
that and fake out the remote-sense inputs of the supply to servo the
current.

We buy a nice 150 watt MeanWell, all approved, emi filtered, PFC
switcher for under $40.

Oh, I have a question for you. Could you email me?

John

jjlarkin/highlandtechnology/and.the.rest



.

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