11
\$\begingroup\$

I have been using and making LED flashlights for years now and I am VERY familiar with all of the circuitry and technology inside of them, but I just got my first LED house light bulb that runs off of 110v AC electricity. It is very similar to a flashlight - it has a large heatsink, and 1 or more LEDs inside of it (brand and specs of emitters, I do not know). The part that I am most curious about is how the electricity from the socket gets to the emitter. In a flashlight the power comes from a DC battery through a current regulator (LED driver) and into the LED itself. This is not difficult because the voltage of common LED emitters is about the same voltage as Lithium batteries (3.7v, 7.4v, etc) which makes the current limiting relatively simple coming from a one or two cell light.

How does this work for a high voltage AC bulb? Is there a transformer and rectifier inside of EVERY bulb (I sure hope not), or are the emitters manufactured to run off of 110v AC power and just use half of the wave cycle?

\$\endgroup\$
  • \$\begingroup\$ The reality is closer to halfway between what you're saying. They are more like switching AC/DC converters. Not a large, bulky transformer but it is definitely complicated electronics inside of there. You have a full suite of power conversion and power sensing circuitry in each bulb. \$\endgroup\$ – scld Jul 24 '13 at 17:16
  • \$\begingroup\$ Ohh, I forgot about switching power supplies (I've never used/made one personally), but I am familiar with them. That makes more sense than a transformer... but still seems very inefficient and bulky. \$\endgroup\$ – Sponge Bob Jul 24 '13 at 17:21
  • 2
    \$\begingroup\$ @KeeganMcCarthy Au contraire, switching supplies are highly efficient and tiny. \$\endgroup\$ – Passerby Jul 24 '13 at 18:03
  • 1
    \$\begingroup\$ They can even put entire 1A switching regulators in a single (large) 24-pin IC. \$\endgroup\$ – Ignacio Vazquez-Abrams Jul 24 '13 at 18:17
  • \$\begingroup\$ @IgnacioVazquez-Abrams I believe that is how the little cube-like iPhone chargers operate. \$\endgroup\$ – Sponge Bob Jul 24 '13 at 19:47
12
\$\begingroup\$

There are several circuits on the internet from noatable sources that show how LEDs can be powered directly from an AC supply without a transformer. Here's one from ON semi: -

enter image description here

And here is the document it came from. The document is entitled "High Current LED - capacitive drop drive application note".

Here is another interesting article, this time from EDN. It shows the following diagram, again transformerless: -

enter image description here

And another article and circuit here: -

enter image description here

\$\endgroup\$
  • \$\begingroup\$ It's a very useful post. You introduce all off available solution for mains led led drivers. I really appropriate it. \$\endgroup\$ – MSS Apr 17 at 15:21
6
\$\begingroup\$

Depends on the led light bulb. Some are direct dc bulbs. These are meant for 12v lamps, not AC lamps. These are smaller, lack the ac rectifying parts, normally set up with 3 leds + resistor or small current controlled ic, in a ceramic casing.

Now LED bulbs that are meant to be replacements for standard 120v incandescent bulbs are very similar to CCFL bulbs. They have AC rectifying section, most are half wave. Then they step it down, then use a current control section to provide the final step for the lighting. If it is a Fading led bulb, there would be more circuitry inside for that.

enter image description here

enter image description here

\$\endgroup\$
  • \$\begingroup\$ Uncommented downvote, yay? \$\endgroup\$ – Passerby Jul 24 '13 at 18:41
  • 1
    \$\begingroup\$ Thanks for the answer and photos, but they don't really answer what happens to the electricity between the wall and the emitter. PS. I wasn't the person who downvoted an hour ago. \$\endgroup\$ – Sponge Bob Jul 24 '13 at 19:56

protected by Community Jul 17 '17 at 3:48

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

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