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I am trying to make a custom dimmer circuit for an off the shelf LED lamp meant for aquatic plant growth. I found a generic dimmer that many people (in the aquatic plant community) use, and am very curious how they managed to make a dimmer so small.

According to the lights it is supposed to be able to dim, it connects to a 24V@(max)4A power supply (input to power supply is 110-230V). The output is directly used by the LED lamp (which we can assume uses at least more than 2A).

Some ways to dim LEDs that I found are

1.) PWM into a mosfet...but at min 2A, I feel this thing would get much too hot. The PWM would then need another IC (at least a 555) which I don't think can fit in there.

Edit: It also seems somewhat wrong to control LED's at this amperage with PWM...especially given that there is a blackbox driver circuit that comes after this dimmer circuit and turning that on and off at high frequency seems 'wrong'.

2.) Constant current...I'm not entirely sure how to make a constant current source driver. I would imagine that this would be in the actual lamp circuit rather than the generic dimmer circuit or generic power brick. Also this dimmer is adjustable, which I am not sure how you would do in a small space for a constant current driver.

3.) basic buck converter to limit the voltage coming in. The issue again is with how you can dim this dynamically with button presses.

I can imagine building any of the three options above to control high power LED's, but I can't wrap my head around how I would go about making the result so small...

Short of me buying the thing and taking it apart, it would be great if anyone had ideas on this!

enter image description here

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    \$\begingroup\$ I think you will be pleasantly surprised about how much power a small MOSFET can handle. \$\endgroup\$ – user253751 Dec 30 '19 at 13:19
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For sure it's using PWM to control the lights via a MOSFET.

A tiny SMT MOSFET can easily control a few amperes at 24V and remain very cool. The controller chip is probably an ASIC or a microcontroller, given the up-down button control scheme. It might take 10 or 15 components total including the power supply for the controller.

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  • \$\begingroup\$ Are there issues in driving high power LEDs w/ PWM? It is only hearsay, but I read around some forums that PWM can be damaging to LEDs? Also what if the LEDs are preceded by some other driver circuitry...can PWM potentially damage that? \$\endgroup\$ – user947659 Dec 30 '19 at 5:23
  • \$\begingroup\$ It depends on what's inside what you are calling the "LED". If it's just an LED (or, more likely, a series/parallel arrangement of LEDs) plus one or more series resistors, PWM can only improve the life. If there's some active drive circuit in there, it's possible it might not like the PWM. \$\endgroup\$ – Spehro Pefhany Dec 30 '19 at 5:24
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    \$\begingroup\$ I don't think there's anything there but LEDs and resistors- maybe on an aluminum backed PCB (?). The value of the resistors is a clue. \$\endgroup\$ – Spehro Pefhany Dec 30 '19 at 5:38
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    \$\begingroup\$ Looks like a nice product to me. Meanwell is a good company, so if it's genuine it should meet the datasheet specifications with room to spare. \$\endgroup\$ – Spehro Pefhany Dec 30 '19 at 6:01
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    \$\begingroup\$ Update: got it working with just a mosfet as you said! I'm using the NTE239 Edit: with a 1k hz pwm, it is quite a beautiful dimmer :) \$\endgroup\$ – user947659 Dec 31 '19 at 4:23

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