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I can't find a comparison of various DC-DC CC/CV buck modules, for example googling XL4015 xl4005 lm2596 review does lead to anything that helps me understand their strengths and weaknesses, and which to choose.

Looking to permanently modify an 110V AC lamp containing an LED so I can use it in my 12V car. I realize I could probably just plug the lamp's AC/DC adapter into my 12VDC to 110VAC inverter, but I'm not interested in that.

My plan is to cut the lamp's DC power cord and wire it to some or another buck converter, wired to a cigarette lighter outlet.

The lamp assembly cannot be disassembled without destroying it, so I don't know much about the LED.

enter image description here

Full size image: https://i.stack.imgur.com/0b1La.jpg

The lamp cord plugs into the AC adapter, which plugs directly into the wall outlet. The label on the adapter says Intertek, 7V, 430mA, KMV-070-030-NA-2.

I plugged the cord half way into the wall adapter, then probed the prongs on the end of the cord with a multimeter, 6.75V 200mA.

Here are two modules that I considering, but am just guessing that they would be appropriate. I selected them because they are small (though space is not an issue) and they provide adjustable constant current and voltage output, and have higher max amps than I need. Besides different buck ICs, they seem to have different coil types. I'm not sure how to interpret either of those differences.

enter image description here enter image description here

Full size images are here:

https://i.stack.imgur.com/R2cS4.jpg

https://i.stack.imgur.com/Sf3hP.jpg

Info from sellers:
    Price               $3            $4
    IC Mfr              TI            XLSEMI
    IC model            LM2596        XL4005
    Op-Amp                            TI LM358
    Input voltage:      7V-35V        5-32V DC
    Output Voltage:     1.25V-30V     0.8-30V DC
    Output current:     3A max        50W/3.5A Sustained 75W/5A Peak
    Efficiency:         92% max
    Switching freq:     150KHz        300KHz
    Output ripple:      50mV max
    Load regulation:    ± 0.5%
    Voltage regulation: ± 2.5%
    Operating temp:     -40 - +85℃
    Size:               48x23x14 mm   51x26x14mm

Datasheets from mfrs:

http://www.xlsemi.com/datasheet/XL4005%20datasheet.pdf

http://www.ti.com/lit/ds/symlink/lm2596.pdf

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closed as off-topic by Andy aka, RoyC, PeterJ, Sparky256, Lior Bilia Feb 22 '18 at 16:08

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  • 1
    \$\begingroup\$ Do you have access to a laboratory power supply? If not, I would get a 12 V buck with variable output, a resistor and find out if your lamps cas internal constant current or current limiting circuitry. It probably does and then all you need to to is buck down 12 V to 7.4 V. \$\endgroup\$ – winny Feb 1 '18 at 7:13
  • \$\begingroup\$ To make a decision about what you should buy you should write out your spec for what you require. You're already started: Input/Output voltages and current capabilities. Do you have physical space requirements?For $3 and $4 it would probably be worth buying both and experimenting a bit if you intend on doing anything similar in the future. \$\endgroup\$ – loudnoises Feb 1 '18 at 7:23
  • \$\begingroup\$ No, that is what I ment. If you don't have constant current regulation in your buck, you will need to either get a resistor and find out of the LED module does or just risk it and apply voltage. \$\endgroup\$ – winny Feb 1 '18 at 10:20
  • \$\begingroup\$ LED could want more than 12v, in which case a buck won't work. you can get a combo boost+buck like those shown. if it is under 12v, either will work. the one on the left handles more current. all else equal, get the ones with larger conductors and capacitors. you don't need the third pot of the one on the right (uc ratio) unless you're charging batteries. \$\endgroup\$ – dandavis Feb 1 '18 at 11:56
  • \$\begingroup\$ Then no problem. Dial in 6.5 V and 200 mA, hook it up and you are good to go without 110 VAC. \$\endgroup\$ – winny Feb 1 '18 at 17:15
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Looking to power an 110V AC lamp containing an LED with my 12V car. The lamp assembly cannot be disassembled without destroying it

Since you cannot connect to the LED directly (bypassing the circuit which converts 110 V AC into whatever DC voltage and current the LED needs) the DCDC converters you propose are useless for this.

What you need is a module which converts 12 V DC into 110 V AC, these are often referred to as inverters. Here's an example

enter image description here

However, there can be issues with using such a cheap inverter. It works not at 50 or 60 Hz (like mains AC) but at a much higher frequency, like 50 kHz.

It depends on the design of your LED lamp if it can accept that. If it has a capacitive dropper circuit inside, there will be issues. Issues in the sense that your LED lamp can break.

There are also 50 / 60 Hz inverters available but these are much more expensive as these need a much larger transformer. Look for a box which can be used to provide 120 V or 240 V AC and is powered from a car's battery, here's an example:

enter image description here

But you're really much better off getting an LED lamp suitable for 12 V. There are plenty available if you just look for them.

But back to your actual question, the difference between the DCDC converters.

Both modules are quite similar in how they work. It depends on your needs which one is suitable, often both are equally suitable. But since we cannot access the LED, we do not know what we need. You made a table comparing their specifications. Look at the differences and those are the differences.

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  • \$\begingroup\$ Aren't car laptop chargers jus DC/DC boost converters from 12V to around 19V? \$\endgroup\$ – Jan Dorniak Feb 1 '18 at 16:10
  • \$\begingroup\$ @JanDorniak They can be indeed, I was thinking about the ones that simply make 120 / 240 V AC so you would need to use the AC power adapter as well. \$\endgroup\$ – Bimpelrekkie Feb 1 '18 at 16:36
  • \$\begingroup\$ that is a bit non-obvious (in my mind the second kind is rare) - could you please clarify? \$\endgroup\$ – Jan Dorniak Feb 1 '18 at 16:37
  • \$\begingroup\$ I have updated my answer to include a picture of the kind of device I was referring to. \$\endgroup\$ – Bimpelrekkie Feb 1 '18 at 16:38
  • \$\begingroup\$ Thank you, it's much clearer now. And you're right on point - why bother using mains devices in a car when there are 12V replacements. N.B. 24V lighting is more common where I come from (apart from LED strips) - in that case a DC/DC boost would be needed. \$\endgroup\$ – Jan Dorniak Feb 1 '18 at 18:14

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