Replacing an UHE video-projector lamp with a high brightness LED array

Discussion in 'The Projects Forum' started by ErnestoRmz, Jul 9, 2010.

  1. ErnestoRmz

    Thread Starter New Member

    Jul 9, 2010
    3
    0
    Hi,

    I'm trying to connect a standard video projector balast power supply ( 80 VAC / 1.6 A / 128 W) to a hight brightness LED array (28.3 VDC / 2.1 A / 59.4 W)

    I did test a 150W / 125 VAC resistive load and the power supply did start up with no problem, so I'm not worry about start sequence any more

    I got the following options

    a) To dim AC voltage with a simple SCR dimmer circuit to a required value and then use a rectifier bridge to connect the LED array as a load

    b) To use a step down POWER SWITCHING REGULATOR such as L4960

    c) To use a linear voltage regulator such as LM350

    d) To use a DC - Dc converter

    The issue here is that I haven't found any solution that fits all the required power needs.

    Any suggestions?

    Thanks in advance
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Why not just get one of these supplies: http://www.mpja.com/Category/Power_Supplies/PowerSupply1_-_Mfg/28V,_5_5A_POWER_SUPPLY_16033_PS.asp
    Datasheet: http://www.mpja.com/download/60watt.pdf
    $41 + shipping, add a power cord and you're done.

    Otherwise, you'll be fiddling around with trying to build your own for weeks, if not months - and you will at least need an oscilloscope in order to troubleshoot a switching supply.

    Unless you already have at least an intermediate skill level, you would have a very tough time completing a switching supply. You would need a flyback-type or push-pull, which involves making a toroidal transformer. Even calculating everything out, you may still have to "tweak" the design to make it satisfactory.
     
  3. ErnestoRmz

    Thread Starter New Member

    Jul 9, 2010
    3
    0
    Thanks a lot for your quick response

    The thing is that I want to take advantage of the existing power supply already built in the projector. It is a ballast type of power supply. So I was wondering if could be something that can be used between this power supply and the LED array in order to substitute the standard UHE lamp with a cost effective alternate solution.

    The bigger issue with this power supply that you mentioned is the cost and the size. I did look at some other 2 years old recommendation of yours (http://www.dimensionengineering.com/AnyVolt3.htm) and it looks interesting but I'm still out of the power requirements
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    OK.
    You've a tough road to go then, if you are a n00b to electronics. You'll need a push-pull DC-DC converter, and that's going to be fairly complex.

    Do you have an O-scope, and a month to kill on this project? If not, you'll need to buy one, and free up some time.
     
  5. Wendy

    Moderator

    Mar 24, 2008
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  6. ErnestoRmz

    Thread Starter New Member

    Jul 9, 2010
    3
    0
    Thanks Bill, the whole idea is to use the existing one, to buy a separate one would turn this project in to a pointless one
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    See the attached for one possible solution.

    The simulation was made in Linear Technology's LTSpice.

    Not bad at 92.4% efficient.

    You would have to wind your own toroidal transformer. It's not that difficult to do.

    Since you're powering LEDs, you really would need to regulate current rather than voltage. In that case, R3 is replaced by the series string of LEDs, and R4 is changed to a 0.39 Ohm 3W resistor. The feedback voltage the regulator is looking for is 800mV. 2.1A * 0.39 Ohms = 819mV. 0.39 Ohms is a standard value of resistance that is nearest to 0.38095 Ohms.
     
    Last edited: Jul 14, 2010
  8. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,348
    Hello,

    @SgtWookie.
    Keep in mind that the input is 80 Volts AC.
    (as stated in the opening post from the balast supply).

    Bertus
     
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