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I'm aware that LEDs need to have their current limited and cannot be connected directly to an unregulated power supply or they will 'blow'. However, can I use a LM2596 DC to DC converter to drive them or will that have the same problem?

The LEDs in question are a set of Christmas lights normally powered by 4x AA batteries but I want them to be mains powered. I'm unsure if there are any series resistors in the LED circuit as it's a sealed unit.

This is what I have: https://www.amazon.co.uk/Valefod-Efficiency-Voltage-Regulator-Converter-%208-Pack/dp/B07DYP6L35

To clarify, I want to remove the existing "control box" entirely as you have to press an On button each time you want the lights to come on, so I'm removing the existing driver and just want to replace it with something which can be switched externally. Therefore I don't think any current limiting is in place?

Null
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NickG
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  • *The LEDs in question are a set of Christmas lights normally powered by 4x AA batteries* That means you need a supply that behaves as a 6 V battery. Batteries behave as **voltage sources**. Yes LEDs need a limited current but since these lights run from batteries (= voltage source) the current limiting is already taken care of. So you need to make the DCDC converter output **6 V** and you're set. **You do not need a constant current source for these christmas lights!!!** – Bimpelrekkie Dec 31 '21 at 18:41
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    What I would try: take an (old) USB cable and strip the wires. Connect the + and - leads (usually red+ and black-) and connect that **directly** to the battery contacts (of course, without batteries in place). Then connect that to a USB phone charger. That would probably work and will be much simpler than messing with a DCDC converter. Yes USB, is only 5 V but very often, that's still enough for some LEDs. – Bimpelrekkie Dec 31 '21 at 18:43
  • Ahh - please see my edit. I want to remove the existing driver... See my edit for the reason. – NickG Jan 01 '22 at 16:30
  • yes, but to do it legit w/o a constant current feature on the buck, keep the current low so that the CV output won't slowly heat the LEDs and cause thermal runaway. or tuck in a modest resistor through the output. – dandavis Jan 01 '22 at 20:33

1 Answers1

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Often a device that runs from 4 AA batteries can instead be powered by from 5V from a "USB charger" this is because batteries drop in voltage to a little over 1V before end of life (and rechargables start at 1.25V) so the 5V is within the acceptable 6V-to 4V voltage range of a series 4 cell pack.

Jasen Слава Україні
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