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Are the default LED currents safe?

user4817590
Prodigy 80 points
Other Parts Discussed in Thread: DLPC350

Hi,

in the manual of the LightCrafter 4500 it says "Exceeding more than 4.3 A for continuous or simultaneous LED operation can damage the LightCrafter 4500 LEDs.". The default LED values applied to the formulas provided to calculate the LED currents result in a total current usage of 7.3A (unless I am calculating it wrong). Does that mean that with the default LED currents it is unsafe to display an all white image for an extended amount of time? Is there a different between video and pattern mode? In pattern mode the projected image seems to be brighter. My main concern is: is it safe to display an all white pattern in pattern mode for a long time? If not, what is the recommended maximum time?

Many thanks,
Jan

  • 0
    TI__Mastermind 30600 points

    Hi Jan,

    You are correct that the default values yield a total current usage of 7.3A but that assumes that all the LEDs are on at the same time. In the default splash screen state, it's in video mode and the LEDs are not all on simultaneously.

    There is a difference between pattern mode and video mode. In pattern mode, to create white, all the LEDs are on at the same time. In video mode, a traditional R->G->B sequence is used and your eyes integrate to create white.

    From section 3.2.4 in the user's guide:

    The LED Selection box determines the control of the LED enables signals. Two options are allowed:

    Automatic: LED enables are controlled by the DLPC350 sequencer. In Video Mode, the LED enables are set in color sequential order. In Pattern Sequence mode, the LED enables are controlled by the downloaded Pattern Sequence settings.

    Manual: LED enables are controlled by the check boxes. Checking a color, continuously enables the LED of that color at the given LED current setting.


    With pattern mode, you will want to be careful about displaying white (at the default LED values) for a long period of time. How long is hard to say, but in general, the average current should not be above 4.3A for a significant amount of time, something like a few seconds. A typical pattern mode application has enough dark time and pattern switching that this shouldn't be an issue.

    Hope this is clear. Please let me know if there are any other questions you might have!

    -Paul

  • 0 in reply to Paul Goedeke
    Prodigy 80 points
    Thanks Paul, that clarified things. One follow up: Is it theoretically possible to upgrade the cooling mechanism of the LC4500 EVM, e.g. a bigger fan or something?
  • 0 in reply to user4817590
    TI__Mastermind 30600 points
    I would say theoretically, yes, but I haven't seen it done on this particular platform. You could try to mount a second fan or do something to improve the heat sink. One thing you might do is try to cool the base of the EVM. If you did some sort of liquid cooling, you could probably dramatically improve the thermal performance because the base is part of the heat sink.