[SOLVED] Produce Flickering of Light Bulb

[Jay_]

Hi guys,

How do I produce flickering effect (at a desired frequency) of a light bulb working in 220 V (mains)? If I was working with say LEDs, I guess I would step-down the mains voltage, convert it to a square wave of lower duty-cycle which would switch on-off the LEDs.

How do I produce this effect with a light bulb (say 40 or 60 W)? Because the light bulb needs to be in full brightness and it would become dim I guess if I made the voltage lower from the 220 V mains.

 

[KJ6EAD]

There are several way to accomplish what you want. Most use a microcontroller with a pseudorandom flicker program and adjust the duty cycle and pulse width to get the effect you want, then output to a triac through an optocoupler. This link has lots of sources including a kit from North Country Radio that probably fits your needs: Flickering Lights - Theory.

 

[Jay_]

I don't think I can connect a microcontroller, because I have no idea on how to program it. I thought I would use an IC like 555 to produce the required duty cycle and pulse width. I checked your link and it may have something useful. Thanks a lot.

 

[Archerman]

You can use your 555 timer and then drive either a TRIAC, 2 SCR's, or a MOSFET. There is also light bulps available working on 32V if you don't want to use the 220V.

 

[JayantD]

Try MOC30xx series opto triac drivers. See Fairchild application note AN 3006.

 

[Jay_]

Could anyone give me a circuit diagram? I plan to use a 40 or 60 W bulb with 240 AC mains as supply. The type of flickering I need isn't "random" or anything, I just need the bulb to go on and then become dim, again on and then dim. I would prefer something like this: 500 ms on, 100 ms dim and repeating. I could easily use IC 555 to give the required duty cycle, IF I had something like but IC 555, but right now I can't because it doesn't work on 240 AC and I need to use a bulb which works in 240 AC. What would be the simplest circuitry to do this? I don't have knowledge too much of programming 8051 and even if I did get the program, I don't know how exactly to feed that program into the micrcontroller.

Would there be a problem (like to the bulb, or the tungsten filament in the bulb) if a 40/60W bulb working with 240 AC flickers?

 

[kabiru]

You can step down the voltage to a required supply needed for the oscilator by using a resistor and zenar diode.

 

[Jay_]

Do I need an oscillator in this? I could easily generate a square wave using 555, but maximum Vcc for IC 555 is 15 V DC which is the problem. Even if I did step down the voltage, I want the bulb to get supplied by 240 V AC mains, I would have to step up the voltage again, wouldn't I?

Could anyone give me an easier way to do this? Even if not the flickering effect, the bulb needs to produce a star-like "twinkling" effect. What would be the best thing to do here?

 

[djsfantasi]

You would step down the voltage for the oscillator or 555 circuit. This would then drive the input of a device like the MOC30xx series opto triac driver that JayantD suggested. That device would then control the mains voltage; you wouldn't step up the 15v or so again... Read through the application notes that he had suggested for another explanation, at Applications of Triac Drivers. There are schematics for driving lights, specific notes for 240 Ac mains, etc...

 

[kabiru]

Hi jay,the out put of your oscilator is going to the gate of your traic, you dont need to step up your voltage to high voltage, your triac is capable of driven up to 220voltAC to your load by controlling the gate of the traic.

 

[FvM]

Would there be a problem (like to the bulb, or the tungsten filament in the bulb) if a 40/60W bulb working with 240 AC flickers?

It's life-time will be surely reduced. Switching between "dimmed" and on is more friendly to the filament than hard on/off switching, because most stress is caused by powering a cold filament. Stage lighting systems are often preheating the filaments at a few percent of rated voltage to increase their lifetime.

 

[KJ6EAD]

A twinkling effect is accomplished by having the light on most of the time and imposing a short random off time pulse at a random interval. We used this circuit to create a very effective star prop for a nativity scene in a stage play many years ago: Popular Science - Google Books. We attached strings of miniature white lights to the shimmer control and an equal number were connected directly to power (unshimmered). By physically intermixing the strings in a high density configuration on our star we got a great twinkling effect. It's for U.S. mains so some components may have to be changed.

 

[Jay_]

Thanks all of you .

I got some help here.. will buzz you guys again if I have any doubts.