LED dimmable drivers - Page 1
Forum section: electronics / general

author: Zopsi
author_rank: Contributor
timestamp: June 09, 2012, 09:29:54 pm
content: Does anyone have any experience with LED dimmable light drivers?We have these old LED light bulbs in our home that do not have the ability to be dimmed by TRIACS. Morever, they keep going out (not the LEDs, the board catches fire). All the LEDs are fine and a new board can easily be put in (see pictures) to fix the issue so I was wondering if any of you had any experience with things like this?I browsed through the TI website and did a little webench thing for LEDs with the LM3445. I attached that report as well. It seems to do what I want.My phone camera was a bit fuzzy on the closeup of the board so I will update with a better picture of the board. Also it is important to note that the pictures depict an undamaged light bulb vs the one that started flaming.

author: bilko
author_rank: Frequent Contributor
timestamp: June 09, 2012, 10:54:38 pm
content: Have you tried Supertex ?The HV9910 is a high voltage chip with a low component count to implement what you are looking for. Here's the data sheethttp://www.supertex.com/pdf/datasheets/HV9910B.pdfHere's the link to the demo boardhttp://www.supertex.com/pdf/misc/HV9910BDB2.pdf

author: Zopsi
author_rank: Contributor
timestamp: June 09, 2012, 11:20:17 pm
content: Does that have TRIAC dimming capability or is just PWM? I just breezed through the datasheet and didn't really read it fully. Demo boards are so expensive though and we have ~30 of these broken. I'd either etch the boards myself or send them off to 4pcb.

author: bilko
author_rank: Frequent Contributor
timestamp: June 09, 2012, 11:30:18 pm
content: No you can't use a triac for dimming.Most LED lighting uses constant current drivers with buck boost converters for efficiency.I can't think of an easy way to use a triac without huge inefficiencies using linear design. Just pondering the idea of using a triac to control the led current in an optoisolator which is then connected to the analog dimming section of above chip, might work..Edit:You were probably on the right track with the Ti chip, I don't know of any others that support TRIAC dimming

author: Zopsi
author_rank: Contributor
timestamp: June 09, 2012, 11:33:09 pm
content: Look at the TI PDF I have in the first post. That LM3445 can be dimmed with a triac dimmer.

author: bilko
author_rank: Frequent Contributor
timestamp: June 09, 2012, 11:37:44 pm
content: Just googled another device by Fairchildwww.fairchildsemi.com/an/AN/AN-9745.pdf

author: Zopsi
author_rank: Contributor
timestamp: June 09, 2012, 11:41:39 pm
content: Do you have an aversion to TI? Fairchild is great too just curious.

author: bilko
author_rank: Frequent Contributor
timestamp: June 09, 2012, 11:45:15 pm
content: No aversion, just another option to consider. Ti are good but its worth comparing a couple of different solutions.

author: Zopsi
author_rank: Contributor
timestamp: June 09, 2012, 11:47:14 pm
content: Of course. They both look fairly complex to do by hand so I may have to have a manufacturer do it.

author: bilko
author_rank: Frequent Contributor
timestamp: June 09, 2012, 11:53:19 pm
content: Another thought...Most LED drivers support PWM.If you can measure the phase angle and convert to PWM you will be able to use the cheap PWM drivers.I'm thinking of something like a zero cross detector and fire angle detector into a PIC chip.Some of the TRIAC LED controller chips are quite expensive.

author: Zopsi
author_rank: Contributor
timestamp: June 10, 2012, 12:03:11 am
content: The chips themselves aren't expensive, but the demo boards are quite expensive. That is an interesting thought. I wouldn't know how to implement it though. I would have to do more research.

author: Zopsi
author_rank: Contributor
timestamp: June 10, 2012, 03:57:04 am
content: Well if I go with the triac dimmer LED drivers it is going to cost me 70 USD for parts for 4 of them (just components nothing else).