Triac dimmers can damage certain LED bulbs?

LED lightbulbs for use with triac dimmers have to be made with certain features which prevent the triac's sudden switching from exciting damaging resonances in the led lightbulbs EMI filter.

LED lightbulbs which are not meant for triac dimming do not have these features, and so they may be destroyed by being accidentally connected to a triac dimmer.

Wouldn't it be best to change the old triac dimmers to new dimmers which would be suitable for the new LED lamps? (after all, triac dimmers are really for the old incandescants).
We could have a dimmer which literally turned off for one full mains half-cycle (10ms) by switching at the zero crossings.......this could be the "dimming command coming" code......then , following that, every missing half cycle could instruct a small micro on the led bulb pcb to dim the current down a bit more....or up a bit more if the dimmed down limit was reached.

Surely this is a better way to dim?

The old triac dimmers were easy to install, and so will be easy to dis-install and replace with the new type of dimmer., surely.

treez said:

Wouldn't it be best to change the old triac dimmers to new dimmers....

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Good idea! Now all you have to do is walk door-to-door to every house in the world that uses dimmers, and convince the residents to throw away their old dimmers and buy the new improved ones.

Seriously though, if you manufacture and sell the type of dimmer you suggest, some people will buy them. If you don't, they won't.

Triac dimmers are easy to install/dis-install, and I reckon its a go-er.

It is not possible for any single dimmable LED lightbulb to be perfectly dimmed with each and every triac dimmer on the market.....they all flicker with one particular type of dimmer.....and often won't dim down to zero with all the dimmers.

Not one single dimmable led lightbulb on earth can work well with absolutely all leading edge or trailing edge dimmers on the market......its time for us to say goodbye to trailing edge or leading edge dimmers

In addition to the problem of widespread use of phase control dimmers, if you change to a cycle stealing system you introduce severe flickering. Imagine a lamp set to say 10% power, on a 50Hz mains supply you would only pass 1 in 10 cycles and that would result in an annoying 5Hz flicker.

One of my designed but not yet tested projects uses power line communication from the dimmer control to the light fitting but uses PWM at high frequency (~1KHz) generated at the LEDs to do the actual dimming. If only there were more hours in the day to complete all my projects!

Brian.

if you change to a cycle stealing system

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yes, but please forgive my poor explanation, our circuit is not a cycle stealing circuit.........the cycle is only stolen the once, and means "dim the lamp"....it is interpreted by the led bulb........when you are not pressing the pushbutton switch, there is no cycle stealing.

I understand. There is a still a control problems though, your 'command set' is extremely limited and can only work at very low speed. For example, if your lighting was to be dimmed from 100% to off in say 1% steps, how do you change from one setting to another? Dropping a cycle may tell the lamp controller to increase or decrease by some amount but how do you tell it to suddenly go from one level to another, especially in big jumps?

The system I developed used slow (300 - 1200 bauds) serial data which carried an address byte and a level control byte so it was possible to use one dimmer to control any one of 256 lamps or any number of lamps in up to 256 groups, sharing the same wiring, to about 0.5% power precision.

I actually use LEDs here to light my swimming pool and use PWM to control their brightness. It's an outdoor pool and I'm also a keen astronomer, the last thing I want is a bright light around me when I'm trying to look through a telescope but equally, I don't want to step backwards into the pool in the dark. The PWM electronics are in a box inside my plant control room, about 50m away from the house and I control it from a computer inside the house. Initially I made it able to select 16 equal steps of light level but I found it difficult to set the levels 'just' right so I modified it to select 1023 levels instead. It's overkill but works nicely!

Brian.

I see what you mean, yes I agree that the method i described is limited, and fairly slow. Though it would be cheap. I presume in your led bulbs you have those communications transformers which pick the data off of the mains live and give it to the micro in the bulb...
To be honest, I think your method would have a definite market for those customers, probably quite a few, who would be willing to pay for that.
If the truth be known, I suspect most households don't actually have dimmers at all, or at least if they do, only on a few light switchs.

I'm not sure a circuit that looked for missing cycles (or half cycles) would be less complicated than one using a carrier based comms system. My pool lights are in constant use and work fine but I never implemented it throughout the house, it never got past the design stage due to lack of time. What I proposed was simpler than a transformer though, I was going to run the entire lighting system off 12V and superimpose a 0.5V data stream on it. While that sounds silly in most situations, you have to bear in mind that the electricity supply here is pretty bad and frequently fails so the house has a backup 12V supply anyway. The backup is only four 5mm white LEDs in each room but it's enough to make it safe if the mains fails at night time. I'm planning (big ambitions!) to demolish my house and rebuild it next year so the plan is to use low voltage LED lighting throughout as the main room lights and use a central 12V battery-backed supply for the whole building. The advantage of using the superimposed voltage drop is a simple comparator can be used to recover the data.

The same principle can be used on larger domestic or industrial lighting systems if the 'signal transformer' method is used though.

Brian.

yes they used the mains cables (also) as comms wires when I worked in a lighting co, and sent data down it for dimming...and used the said signal transformer you speak of.

Anyway, here is the led lightbulb with dimming circuitry, as per the "missing cycle" comms "protocol".
Also, shown is the "Wall Dimmer" which goes with this led lightbulb