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I have one DC input 24V, 5A. I have designed a 4 channel led driver using the PAM2804 for Cree RGBW leds. I am using 3 of them. So, 3 Rgbw leds, and 3 led drivers. I need to be able to control individual r,g,b,w channels, and select if I want to use 1,2 o 3 leds. An arduino supplies the control signal to the PAMs.

My question, is how to convert the 24V, 5A into four 5V, 3A(max) sources. I hav been using LM2596, or XL6009E1, to convert 24V into one 5V, 3A source. But connecting several LM2596s in series to a 24v power supply seems not to work, one of them gets almost all the voltage. I have used them both in adjustable and fixed output. What can I use instead?

EDIT the picture shows 12V 5A; that is not correct, it is 24V 5A; as described in the text description. Thanks for pointing it out.

enter image description here

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  • \$\begingroup\$ Well, 12V*5A = 60W. But (5A*5V)*4 = 100W, so this supply won't have enough power for all of the LEDs, not including losses (another 15% probably.) \$\endgroup\$
    – rdtsc
    Apr 2, 2021 at 12:00
  • \$\begingroup\$ The question says 24V 5A but the schematic says 12V 5A. Which one is it? \$\endgroup\$
    – Kartman
    Apr 2, 2021 at 12:08
  • \$\begingroup\$ XL6009 is primarily a step up converter and needs two inductors for step down. For more efficient step down use a buck-mode module eg. ebay.com/itm/… and always underrate it! (eg. for 3A use a 5A module). \$\endgroup\$
    – Bruce Abbott
    Apr 2, 2021 at 20:48

1 Answer 1

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Your LED drivers are controlled by the same micro, so everything must have a common ground.

I don't understand the "series" confusion, there is nothing to be wired in series here.

What you need is a 5V power supply for 4x 3A loads, so a 5V 12A load.

You can replace your 24V power supply with a 5V 15A mains power supply, or use a sufficient number of step-down DC-DCs to get 5V at the required current. For example if you get 5V 3A DC-DCs you need four, one per LED board.

Please do not buy the famous cheap counterfeit LM2596 modules from the internet, every component is fake, starting with the LM2596 obviously, but the caps are also garbage and they will die.

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  • \$\begingroup\$ First of all thanks. "..or use a sufficient number of step-down DC-DCs to get 5V at the required current. For example if you get 5V 3A DC-DCs you need four, one per LED board." This is what I tried, using the LM2596 as Dc-dc converter. But using more than one, I can only connect them to the 24V in parallel or in series. Do you recommend another kind of dc-dc step down? Thanks \$\endgroup\$
    – Madaeon
    Apr 2, 2021 at 11:40
  • \$\begingroup\$ Connecting the supplies in series won't work - as you've found out. They should be connected in parallel. Have you tried this? \$\endgroup\$
    – Kartman
    Apr 2, 2021 at 12:05
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    \$\begingroup\$ The whole point of a switching converter is efficiency. If it has 85% efficiency, and it outputs 5V*3A = 15W, then it inputs 15W/0.85=17.6W or 24V*1.36 Amps. So your 24V power supply is fine. Note I will not bet on the efficiency of the counterfeit LM2596 modules. Please use something with components on it that were not found behind a dumpster in Shenzen. On the ones I tested, the 85°C general purpose capacitors were finger-burning hot, way below rated load current, which it did not reach. \$\endgroup\$
    – bobflux
    Apr 2, 2021 at 12:43
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    \$\begingroup\$ @Madaeon A switching converter isn't like a linear regulator. If the output voltage is lower than the input voltage, the output current will be higher than the input current. 5 V at 3 A is definitely achievable from a 24 V 1.25 A input, you don't even need a particularly efficient converter for that. With a linear regulator, the output current is equal to the input current, so you couldn't use one of those for this, but switching converters are capable of doing what you need. \$\endgroup\$
    – Hearth
    Apr 2, 2021 at 13:11
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    \$\begingroup\$ @bobflux I'm not sure where you get 1.36 amps on the input--it would only take 0.735 amps on the input to equal 17.6 watts at 24 volts. Typo in the calculator? \$\endgroup\$
    – Hearth
    Apr 2, 2021 at 13:13

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