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I have a chip-on-board LED that requires 36V max, 300 mA, but I have a power supply designed for a 12V max, 900 mA LED. The power supply is a pretty standard constant current power supply that outputs 900 mA for the LED and adjusts the voltage as required.

Is there a simple way to take this output and convert it from 900 mA to 300 mA without disrupting the constant current power supply's regulation? I am aware things like buck converters exist but I am unsure if they will function properly in this instance.

Link to the LED in question

The power supply is part of a larger unit and cannot be replaced. Solutions that only supply partial power to the LED (at least 5W) would be acceptable.

Update: I dug the old power supply out of the unit and discovered it is capable of 16V max at 16W max. It supplies 1A at 10.06V to a LED currently.

Link to the power supply currently used (Model: RLDD015L-1000)

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  • \$\begingroup\$ Definitely not without abandoning the existing regulation. There are of course step-up drivers for higher voltage LEDs but those either do the regulation or need it to be re-created. There might be a way to "game" the existing driver into a power supply, but you'd probably be better off starting with an ordinary voltage mode supply (vs LED driver) or really just buying a power supply/driver directly compatible with your LEDs. \$\endgroup\$
    – Chris Stratton
    Sep 28, 2020 at 17:51
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    \$\begingroup\$ You won't get 36 volts at 300 mA from a 12 volts (max) limiting current at 900 mA (due to power conversion efficiency being about 90%) \$\endgroup\$
    – Andy aka
    Sep 28, 2020 at 17:51
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    \$\begingroup\$ What kind of LED board requires "36V max"? That's suspicious - can you provide a link or schematic? \$\endgroup\$
    – td127
    Sep 28, 2020 at 17:59
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    \$\begingroup\$ You'll probably want to switch to a boost regulator with it's own current regulation. \$\endgroup\$
    – Drew
    Sep 28, 2020 at 18:05
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    \$\begingroup\$ How does the existing driver work? Does it use PWM? So the average output current is 900mA * duty cycle? What is the switching frequency? \$\endgroup\$
    – mkeith
    Sep 29, 2020 at 5:13

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Solutions that only supply partial power to the LED (at least 5W) would be acceptable.

It may not be possible with what you have at hand.

Most 36V-COBs start to illuminate at 25-28V. For yours, it could be around 28V/10mA (I'm just guessing as there's no datasheet available.). So there's no chance to drive that LED with your LED driver as the max allowed output voltage is 12V.

Even if the LED driver is part of another system and cannot be replaced, you may have an option to use a separate, appropriate LED driver only for that LED. Or, if it's not vital to use that LED, maybe you should consider using a different one that your LED driver "likes".

But remember that,

  • You can't use your existing LED driver,
  • You can't convert 0.9A constant current (12V max) to 0.3A constant current (36+V max). If someone knows a CC-to-CC converter, please let me know.
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  • \$\begingroup\$ OK, I retracted my simplistic answer of just generating 36V. You're right - these constant current devices are different animals. Thanks! \$\endgroup\$
    – td127
    Sep 28, 2020 at 20:08
  • \$\begingroup\$ I actually know experimentally that it pulls about 15 mA at 29V, so you are very spot on. a CC-to-CC converter seems like what I would want but like you mention I have never seen one even as just a circuit. \$\endgroup\$
    – Tristan Maxson
    Sep 28, 2020 at 21:12

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