I was looking for a dimmer to control an LED strip with following characteristics:

  • 5 meters long
  • 14,4W (max) per meter, so 72W in total
  • 24V

I found a dimmer on ebay that says it can handle 144W, which looks like this:
I'm having a hard time believing something so small can handle that much power.

My question is: can it?

Follow-up: if so, how? Is this a custom chip? I've also read something about those things using Silicon-Controlled-Switches or Silicon-Controller-Rectifiers, something I know very little about, obviously.

  • \$\begingroup\$ with a 10mOhm FET, you would be dissipating 14 watts at 12 amperes in the on state. It is possible but I think that thing would get hot. \$\endgroup\$ – HL-SDK Jun 2 '14 at 16:54
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    \$\begingroup\$ @HL-SDK 0.01 x 144 = 1.44 Watt, not 14.4 \$\endgroup\$ – Russell McMahon Jun 2 '14 at 17:01
  • \$\begingroup\$ I'd be most concerned about the connector handling it. \$\endgroup\$ – John U Jun 2 '14 at 17:53
  • \$\begingroup\$ Also, it's worth keeping in mind that whatever dissipation you determine, it only applies at 100% power (for a perfect switcher). Disregarding losses during transients, at 50% power it will only dissipate 50% of max. Of course, you can't actually disregard transient dissipation, so the whole thing gets more complicated. \$\endgroup\$ – WhatRoughBeast Jun 2 '14 at 18:41

Can this dimmer really handle 144W?

144W at 24V = 6A.

If you PWM a FET so it is on or off it will dim LEDs that are connected using constant current or with a series resistors.

10 milliOhm Rdson FETS are easily enough available.

Power dissipation when on = I^2 x R = 6^2 x 0.01 = 0.36 Watts.
MOSFETS with 5 or 2 or even 1 milliOhm omnn resistance are available. Even 0.36 Watt would be acceptable.
So, yes-maybe. ie it's possible to design something that would.
Whether it does is TBD.
The price is right to find out :-).

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  • \$\begingroup\$ Maybe they run it at 144W to shrink the "housing" onto the board. \$\endgroup\$ – Spehro Pefhany Jun 2 '14 at 17:04
  • \$\begingroup\$ are there standard circuits for something like this, or do these have to be custom designed? I'd love to see how they do it, starting from a say a 5V PWM signal (if it's not too much trouble) :) \$\endgroup\$ – DaJF Jun 2 '14 at 20:01
  • \$\begingroup\$ @DaJF - very standard PWM control of a MOSFET is often 'good enough'. The FET is either on or off (except during transistions) so power dissipation is minimised. Simplistically, just applying an adequate level PWM signal to a MOSFET gate is what is required. \$\endgroup\$ – Russell McMahon Jun 3 '14 at 20:40

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