Multiplexing RGB-Leds what is the upper limit of the voltage?

StefanL38

Hi,

a friend of mine wants to build a 6x6x6 RGB-LED-Cube. The On/Off-switching of the LEDs should be multiplexed to reduce the number of wires inside the cube.
Now if the LEDs are multiplexed this means each single LED is switched on for a fraction of the time. To make the LED shine bright I want to increase the voltage.
The averaged current will be adapted to the right value. But how far can I increase the voltage without damaging the LEDs?

Does somebody have practical experience with this?
What are the limiting factors? The short-pulse maximum current mentioned in the datasheet?

best regards
Stefan

Mark_T

You need to control the current, not the voltage - forward voltage depends on temperature and other things, its not safe to set the voltage at a fixed level as thermal runaway can happen. This is why current-limiting resistors or constant-current drivers are normally employed.

Look at the datasheets for the LEDs to see the reponse curves (light against current) and the maximum peak current - exceeding this may damage the devices permanently.