Re: 19,008 LEDs on the wall, 19,008 LEDs

[Eric Smith <eric@brouhaha.com>]

Michael J. Mahon wrote:
> (Scribbling on back of envelope...) If a "lit" LED has an average of
> 10mA of current flowing, and is driven from 5v with resistive losses,
> that's 50mW of power per lit LED, or 50W per 1000 lit LEDs.  So half
> lit would be an average power of almost 500W, and all on (which must
> be handled) a kilowatt, for a 200 amp 5v supply!

I think you would want the average current of a lit LED to be substantially
less than 5 mA.  Were I doing such a thing, I'd probably try for a
duty cycle of around 5%, and about 20 mA active current, for an average
of 1 mA.

And I'd probably avoid the resistive losses by eliminating the series
resistors and using switching regulators configured to regulate the current
rather than voltage.

The HP-35 calculator, introduced in 1972 as the world's first handheld
scientific calculator, used inductive LED drive for the same reason.
All the energy went into the LEDs rather than having a significant
fraction burned up in current limiting resistors.

Eric