Dimming of LED with triac

Thread Starter

Saiteja chinthalapati

Joined Oct 25, 2018
97
I have LED tube which is 230 V AC dimmable. I want to develop a circuit for dimming using triac and potentiometer. Can anyone suggest me the best reliable circuit
 

pmd34

Joined Feb 22, 2014
527
Im not sure this is very practical, without adding in a more complex current limiting circuit the triac will just cause the LEDs to flash at 50Hz which is very annoying to the eyes, as it is JUST perceptible.
 

Tonyr1084

Joined Sep 24, 2015
7,852
Did a video about dimming non-dimmable LED's using a single incandescent bulb on the same circuit. In the basement I have a similar arrangement where I have four LED can lights and a single incandescent bulb on the same switched circuit. Though the basement isn't set up for dimming, it has a motion detector that switches the lights on. Without the incandescent, the LED's never shut off completely, and they sometimes flicker. Having the incandescent in circuit - they have worked just fine for the last five years.

Here's the video on dimming LED's with a single incandescent in circuit.
 

Thread Starter

Saiteja chinthalapati

Joined Oct 25, 2018
97
Im not sure this is very practical, without adding in a more complex current limiting circuit the triac will just cause the LEDs to flash at 50Hz which is very annoying to the eyes, as it is JUST perceptible.
[/QUOTE

I am ready to add capacitor / resistor but the circuit should be reliable and i don't want to use any controller
 

Thread Starter

Saiteja chinthalapati

Joined Oct 25, 2018
97
Did a video about dimming non-dimmable LED's using a single incandescent bulb on the same circuit. In the basement I have a similar arrangement where I have four LED can lights and a single incandescent bulb on the same switched circuit. Though the basement isn't set up for dimming, it has a motion detector that switches the lights on. Without the incandescent, the LED's never shut off completely, and they sometimes flicker. Having the incandescent in circuit - they have worked just fine for the last five years.

Here's the video on dimming LED's with a single incandescent in circuit.
Can you share the schematic for reference?
 

Tonyr1084

Joined Sep 24, 2015
7,852
Can you share the schematic for reference?
There is no schematic to share.

The wall switch consists of a light and fan controller that sends radio signals to a receiver mounted in the base of the ceiling fixture. There's a second remote so you can turn the lights and/or the fan on and off from bedside. The control receiver in the lamp fixture is commercially purchased at the local big box store. It's wired into the house wiring just like any other dimmer.

The whole point of the video is to show that you don't have to buy a special dimmer designed for LED and CFL lamps. Simply adding a single incandescent bulb into the fixture or circuit will make the LED's follow along with the brightness. I couldn't tell you exactly why that is - I just know that it works.
 

pmd34

Joined Feb 22, 2014
527
The only way to reliably control an LED brightness is to either switch them off and on very fast, but this usually tends to be perceivable, or to current limit them. Using voltage limiting as with a triac directly will not give you good control, as the actual voltage range from LED just lit, to full power is very small.
That said, you can buy LED dimmable bulbs very cheaply, and the dimmers used are triacs.. so.. I would buy a bulb and take it apart, and either uses the parts or copy the design!
 
+1 to what pmd34 said.

There are dimmable LED lamps, designed to be directly retrofitted in incandescent sockets, and which can be reliably dimmed with the same Triac dimmer used for those incandescent lamps.

I have a couple of installations at home.

Warning: not all LED lamps are dimmable. The ones which are, have been clearly labeled.
 

ronsimpson

Joined Oct 7, 2019
2,985
There are several types of LED bulbs. Two of which are dimmable and non-dimmable.
Many types of bulbs regulate the LED current. Changes in line voltage do not effect the LED current. I know of bulbs that have no change in current from 70 to 150 volts. I designed LED torch/flash light bulbs that work from 3V to 30V with no change in LED current.

Most power line bulbs have diodes and a large cap. They live off the peaks of the voltage not off the average like a incandescent bulb. If a dimmer removes 1/2 of the sine wave the peak will still be the same. The LED will not see a change in power line voltage. To get any dimming you need to remove most of the power wave form so the peak is below 70 volts. At this point the PWM is not regulating and is on the edge of shutting down. The flicker you see is likely caused by the PWM working for 3 half cycles then off for 4 half cycles on for 1-4 half cycles and off for some number of half cycles. Very randomly.
1579013942933.png
Dimmable bulbs: There are several types. It is common to have the same diodes + capacitors. There is a wire from the power line to the PWM's enable pin. If the power line is there 100% of the time the PWM works all the time. Like in the picture if part of the power line voltage is missing then the PWM and the LED current is, stopped for that time.

Why do dimmable bulbs not dim: By looking at the power line after a dimmer, it can be seen there is a large amount of capacitance on the power line. Some of which is from power line filters inside the light bulb. There might be a capacitor inside the dimmer. It just might be the wire to wire capacitance. I found by looking at the power line from a dimmer, at no load the dimmer is not functioning. The entire wave passes through. Depending on the dimmer, a very small load will solve the problem. There needs to be a load to pull the wave to zero during the dead time. The load must be resistive not capacitive. The load must not be diode(s) + capacitor type. Some time a 1 watt resistor is enough to pull the line down.
 

Tonyr1084

Joined Sep 24, 2015
7,852
I did say that LED's will flicker. I also showed that the addition of an incandescent bulb WILL affect the brightness of the LED.
 

Tonyr1084

Joined Sep 24, 2015
7,852
The only way to reliably control an LED brightness is to either switch them off and on very fast, but this usually tends to be perceivable, or to current limit them.
You would be simulating a PWM Power Supply. They don't have to switch on and off at 27 Hz, you can switch them MUCH faster, far beyond the ability to perceive them being on and off. This gives LED brightness an unnatural linearity to them. Un natural because as you show, they depend on current, not voltage. But PWM can dim an LED. I've done it. Many have done it.

Please note the critical part in my video - the incandescent bulb on the circuit. Without it - the LED's did not dim. You can see that in the video as well. Actually I did perceive the slightest amount of dimming, but it was negligible. But with the incandescent bulb - they dimmed the full range of the dimmer being used. THAT dimmer does not dim the bulbs to complete extinguished. I have four LED sconces in my family room. No incandescent bulbs on that circuit. I bought the special dimmer designed for dimmable LED's. I'm not overwhelmingly impressed by the performance though. Nevertheless, I have both systems - dimmable and non-dimmable. I prefer the non-dimmable WITH an incandescent in circuit. Just works smoother and more natural (my opinion).
 
Top