How do dimmable LEDs work?  - Page 1
Forum section: electronics / beginners

author: shaunakde
author_rank: Contributor
timestamp: August 07, 2020, 03:27:30 pm
content: I was looking to build a triac based dimmer for an LED lamp and found that only a few companies (most prominently Phillips) manufacture LED bulbs that support phase control dimming.(I had made one before for a traditional incandescent bulb and just used a bridge rectifier and a SCR with RC triggering something thing like:I was wondering how they detect what the dimmer is set to? Do they have circuitry that checks the phase/waveform of the input line AC and then translate it to a constant current drive for the LED?And why don't more manufacturers make dimmable LEDs? Is it more expensive to manufacture? Do the cost of the components make a significant dent in their profit-margin? Or does Phillips own the patent?Can you modify a regular LED to make it dimmable? Or drive the LED with a PWM signal?Here is some marketing I found while trying to understand what happens:-https://www.youtube.com/watch?v=4e2mlZ627Js&feature=youtu.be- Dimmer compatibility list:https://www.assets.signify.com/is/content/PhilipsLighting/Assets/philips-lighting/united-states/20200127-dimmer-compatibility-consumer.pdf- SCR RC triggering lecture I was following:EDIT: I guess I don't even know how to begin to search for this information - and any "google tips" that might help me in the future will be much appreciated.EDIT2: I don't know how prevent youtube videos from auto-showing in the post

author: Dabbot
author_rank: Regular Contributor
timestamp: August 07, 2020, 03:41:19 pm
content: Google "TRIAC dimmable LED driver" or similar.Here's an example chip which will do it, the BP3216:http://www.bpsemi.com.cn/uploads/file/20161229095524_705.pdf

author: David Hess
author_rank: Super Contributor
timestamp: August 07, 2020, 04:15:02 pm
content: Quote from: shaunakde on August 07, 2020, 03:27:30 pmThere are two ways that I know of. One is to measure the conduction angle like you mention but some LED lamps, including the Cree ones that I have been using, have an RC filter which measures the average line voltage so they will also work with a variac.

author: MarkF
author_rank: Super Contributor
timestamp: August 07, 2020, 05:10:05 pm
content: (Not promoting any of these...)A bunch of videos of work people have done on the subject:Great Scott:Steve Gardner:

author: Zero999
author_rank: Super Contributor
timestamp: August 08, 2020, 08:59:52 am
content: Quote from: shaunakde on August 07, 2020, 03:27:30 pmThat circuit won't work properly. C1 won't discharge. R1 + R2 & C1 simply form a low pass filter. If R1 is adjusted then the voltage on the trigger will vary, causing the SCR to turn on and off, depending on R1.In a proper phase controller, the capacitor is connected to the gate via a DIAC, which doesn't conduct, until a certain threshold voltage is reached, known as the break-over voltage. When the break-over voltage is exceeded, it conducts, discharging the capacitor into the SCR's gate. When the polarity of the supply voltage is reversed, the capacitor is discharged and the cycle can repeat.https://www.electronics-tutorials.ws/power/diac.html