1
\$\begingroup\$

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:
ebay_dimmer
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.

\$\endgroup\$
  • \$\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
  • 5
    \$\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
3
\$\begingroup\$

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 :-).

\$\endgroup\$
  • \$\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

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.