LED Power Adapter Help

[StevenCarls1]

Hello, currently I am working on renovating an LED array project, specifically making the power adapter smaller. Currently, we use a 36V .69A AC/DC wall adapter that's fairly big, around 74x43x40mm with a size m dc power jack (similar to a tri-mag icm24). Inside of the driver, a buck converter reduces the 36V to 24V for the array. In order to make this smaller, I was considering switching to a smaller USB-C power adapter to give the same wattage, then using a boost converter and current limiter, with a pd trigger inside of the cable to get the same result. A question I have for people much smarter than me is if this would be a feasible and smart power connection for a lamp (considering the new aspect of human error this would introduce), if the boost converter would dissipate a large amount of power as heat within the driver, and if there was a smarter solution to this to decrease the overall size of the power adapter without switching to USB-c. Thanks!

[Phil1977]

I´m not smart enough to know if I´m smart enough for your question but I´ll try:

Generally your plan seems quite promising. USB C power adapters are more or less the smallest power supplies you can buy and they can be of good quality if you buy something reputable.
24V is a lucky voltage for the LED array. In the best case the LEDs do not light up with 20V, so you could use a USB-PD trigger for 20V and make a boost converter responsible for the current regulation. Boost converters can exceed 95% efficiency with this load - that means not much more than 1W of heat and that means you don't need any large heat sink.

Do you already have some type of trigger and boost converter in mind? 

[StevenCarls1]

I am unsure of my current PD trigger and boost converter as I'm unsure of the current input voltage I want. The new LED array itself uses 720mA at full brightness, so a 20W or 25W adapter may be necessary, in which case for those I don't believe a 20V PD would exist. The most universal PD option at that wattage I can find is 9V, however I'm assuming that going from 9V to 24V would reduce the efficiency of any boost converter attached by quite a lot, so I'm a bit unsure about which avenue to take.

[Phil1977]

Is it that important for the supply to be that small that you want to use a 20W-supply?

I´d be cautious with a 20W-supply because lifetime of such a supply is worst at it´s maximal power level and a smartphone usually loads the supply for 1 or 2 hours, your LED lamp may load it continuously.

I´d go for a small 45W-supply like this https://www.anker.com/eu-de/products/a2677 (Anker single port 45W). I´d set the trigger to 15V to be safely away from the forward voltage of the LEDs. The reason for this is: Boost converters can't regulate the current if the output voltage is lower than the input voltage. In that case they just blow up your LEDs.

Then I´d take a boost converter specified for 3A input current. That way you could even use the 9V or (inofficial) 12V PD-setting in case you want to run the light from a powerbank or similar.

The dissipations at less than 30W of power won't be too large if you use good components. Yes you´re right, the conversion efficiency will be higher if you go mains-->15V-->LED than if you go mains-->5V-->LED. But the difference between 9V, 12V and 15V of intermediate voltage won't make a large difference. I´d only expect 5V to make trouble because it would exceed 3A.