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DLP2000: DLP use with high power laser sources and active cooling DMD

BGX561
Intellectual 610 points
Part Number: DLP2000

TI,

I recently began experimenting with the EVM for the DLP2000FQC DMD. I successfully got this working with both the Beaglebone and the RPI and have moved on to making modifications to the light engine to determine what else I might be able to do with the DMD.

I read a few posts by @Pascal DLP and @Fizix and was reviewing this doc on use of the DMD with laser sources.

http://www.ti.com/lit/wp/dlpa037/dlpa037.pdf

While this document does address he diffraction, this document does not include is any information regarding the thermal limits and damage thresholds of the mirrors themselves.

From what I can tell from the DLP2000 datasheet http://www.ti.com/lit/ds/symlink/dlp2000.pdf 

I intend to explore this deeper with high power RGB CW laser sources in excess of 1W. In order to do this, it seems possible by actively cooling the DMD. From the datasheet it notes that the equations shown are valid for a 1-Chip DMD system with a total projection efficiency from DMD to screen of 87%.

TARRAY = TCERAMIC + (QARRAY × RARRAY–TO–CERAMIC)

QARRAY = QELECTRICAL + QILLUMINATION

QILLUMINATION = (CL2W × SL) 

TARRAY = Computed DMD array temperature (°C)

TCERAMIC = Measured ceramic temperature (°C) TP1 location in Figure 10

RARRAY–TO–CERAMIC = DMD package thermal resistance from array to outside ceramic (°C/W), specified in Thermal Information

QARRAY = Total DMD power; electrical plus absorbed (calculated) (W)

QELECTRICAL = Nominal DMD electrical power dissipation (W)

CL2W = Conversion constant for screen lumens to absorbed optical power on the DMD (W/lm)

SL = Measured ANSI screen lumens (lm)

This same section goes on to mention a nominal electrical power dissipation to use when calculating array temperature is 0.045 watts.

Since laser power is generally not measured in lm, and we don't care about screen lumens SL, we will use the source directly as 1W, but use the same illumination distribution of 83.7% on the DMD active array and 16.3% on the DMD array border and window aperture used to calculate the CL2W constant. We will assume the mirror array is dielectric coated with a high reflectance in the visible spectrum of nearly 100%, and since the sources are coherent and visible there is no heating caused by IR or UV absorption.

this works out to QILLUMINATION = 0.163*1W = 0.163W.

TCERAMIC = the cold side of a Thermoelectric Cooler. TEC with Qmax = 120W. Assume the TCERAMIC is actively cooled and held constant at 25 deg C.

TARRAY = TCERAMIC + (QARRAY × RARRAY–TO–CERAMIC) = 25 + ( 8 * (0.163+0.045)) = 26.66400 deg C

If this is the correct way of calculating this, then if we assume the same 55.8 deg C max temp that was calculated as an example in the datasheet, and work backwards:

(55.8 - 25)/8-0.045 = 3.80500

3.80500/0.163 = 23.3435583 W

With the maximum rated array and window temp of 90 deg C:

(90 - 25)/8-0.045 = 8.08

8.08/0.163 = 49.5705521 W

Would it be within the product's limits to Illuminate the DMD with up to 50W of 400-700nm laser light if it is actively cooled? Or is this way off and less than 1W will destroy the DMD?

Please advise.

  • 0
    Intellectual 610 points

    Pascal DLP (1082852)

     

    I found another posting addressing something similar at 20 W/cm^2 for VISIBLE wavelengths.

    (4.8384mm*2.7216mm) Active area

    = 0.131681894 cm^2

    2.63363788 Watts

    It seems like 1W would be reasonably safe in this case, especially with active cooling but certainly 50W would be a no-go. I'd appreciate your weigh in on the topic.

    ---

    I can test this tomorrow, just looking for a reasonable upper bound to set as a limit. (For my applications 3-10W are most common, and it would be rare for anything over 30W, 50W being an absolute maximum) 

    For good fun (and in the name of science) it would probably be a worthwhile test to push the  DLP2000 to destruction anyway, since they're fairly inexpensive relative to other DMDs.

  • 0 in reply to BGX561
    TI__Mastermind 47610 points
    Hello BGX561,

    1 W may be possible. 10W will depend on the particular DMD. Many of the smaller DMDs are designed for fairly limited heat dissipation since they are designed for fairly low power applications. Remember it is W/cm^2, so that if you have 10 Watts on a 0.5 cm^2 DMD that is 20W/cm^2.

    The main point is that you want to measure the case temperature in order to determine the array temperature. The better your thermal solution, the more power can be handled.

    I am concerned that with the DMD you mention that the thermal resistance is relatively high and the area fairly small.

    Fizix.
  • 0 in reply to Fizix
    Intellectual 610 points

     ,

    I had two more follow up questions for this thread-- 

    First, 

    The document http://www.ti.com/lit/wp/dlpa037/dlpa037.pdf  addresses the use of lasers with DLP, and the diffraction effects to be expected.

    There is a second document here http://www.ti.com/lit/an/dlpa052/dlpa052.pdf that I found useful in considering the output aperture size to capture the orders with the greatest amount of power.

    The goal is to produce a collimated output beam with varying intensity between the ON state and the OFF state.

    I am aware that the diffractive beamlets will retain the characteristecs of the input beam, i.e. collimated in => collimated out. 


    My current design will use an aperture stop to select only the blaze in the center of the diffraction pattern (0 order) because this is the simplest method for evaluation, but this is a fairly substantial loss of power over the input beam.

    I am wondering if it is practical/possible to "recombine" the collimated beamlets into a single beam using a lens to collect the beamlets from the other orders  .... .i.e. reimage the DMD at infinity. (not sure if its possible redirect these collimated beams to propagate in the same direction)

    ---

    Second,

    When diffraction occurs with the DMD across multiple RGB wavelengths do they all appear "stacked" (i.e. white beam = white dots), or split (i.e. white beam = separate patterns for R, G, and B) ?

  • 0 in reply to BGX561
    TI__Mastermind 47610 points

    Hello BGX561,

    The first paper [Using Lasers with DLP® DMD technology] assumes that the source is CW.  It was written some time back and does not contemplate pulsed lasers.

    The second paper [System Design Considerations Using TI DLP® Technology down to 400 nm] explores the effect of laser diffraction when using small apertures.

    There is a third paper that may also be useful:  http://www.ti.com/lit/wp/dlpa027/dlpa027.pdf  [Laser Power Handling for DMDs]

    Addressing the "beamlets' first let's note that a blazed order is not the same as the 0 order.  It can if all the mirrors are flat.  The 0 order is the order where there is no dispersion.  For a DMD that is operating, the blaze order will always be non-zero.

    This is important because if you have white light, the beamlets will have chromatic dispersion.  This is not a problem if you plan to re-image at a plane that is not at infinity.  If you image at infinity, the colors will have the same spatial separation that they did at the lens that climates the orders, including the chromatic dispersion of each order that you capture.

    This should answer both of your questions.

    Fizix