ElectroMaster said:This 800 W light bulb flasher operates directly off the line and needs no transformer. Power for the timer circuit is derived by limiting the current using a 330 nF capacitor (acts like a 9.6 k resistor at 50 Hz), rectifying with a full-wave rectifier composed of four diodes (you may also use a pre-made bridge rectifier instead of the diodes, of course, but make sure the voltage rating is 400 V, or 250 V RMS). Then the voltage is limited with a 9 V zener diode (almost any of this voltage will work), a 1 W type. The 100 µF capacitor filters the power, a 16 V rating may be a bit safer. Remember: if the zener diode fails, the capacitor will blow because it gets peaks of up to 330 V, although current-limited). In this configuration, the timer gives long pulses at 1.3 Hz.
Now there's one problem: we can't drive the triac directly, because the controlling voltage is not isolated from the line since there is no transformer. The easiest way to drive it is thus by using a triac optocoupler. The K3021 or MOC3021 is well suited for this purpose, as it works like a small triac and thus allows it to directly drive the gate of the larger triac. The coupler is connected to turn on when the timer outputs a low, so we get short pulses.
Please note that this only works with resistive loads like incandescent light bulbs or heaters. It does not work with fluorescent lamps (need a snubber network to do that).
I need the full detail for knowlegde gaining
I agree that we'll only gain knowledge through trying and reading up. It'll be good with guidance.
Here I am trying to use an optoisolator to drive a triac. I tried to pump in a square-wave kind of pulse into the optoisolator MOC 3010 and tried MOC 3020 too. The connection is as attached. This circuit is adapted from the application circuit from the datasheet. Triac I'm using is BT139-600 which I'll like to eventually drive halogen lamp up to 2kW. (My main objective is to be able to use software to vary the brightness of halogen lamps up to 2kW)
Can someone please advise me if my approach is wrong? I'm not really getting the output right, it actually flicker! My mains is 230V, 50Hz, & I tried pumping in 100hz, up to 500Hz then no more flicker. But....I can't control the brightness! I've read and searched for examples, some are using zero-crossing detector then drive the optoisolator. I tried to build that circuit, but it is also not working.
I feel quite dishearted that nothing works, and was thinking is it that triac is not suitable to vary halogen lamps?
Sure you can...If you get a three quadrant triac.Now there's one problem: we can't drive the triac directly, because the controlling voltage is not isolated from the line since there is no transformer.
You should not be dimming a halogen, it breaks the halogen cycle and causes the bulb to burn out.
Dimming Halogen Lamps:
Line voltage (120V) halogen bulbs can be dimmed by regular incandescent dimmers. Using a dimmer with halogen bulbs actually has negative effects. When dimmed, the halogen filaments do not reach the 250 C needed for the halogen cycle to take place. This could cause the inside wall of the bulb to blacken reducing light quantity and life. Running the lamp at full brightness will help restore and clean the bulb.
It sounds plausible, since that is what the halogen cycle does (redeposits vaporized carbon onto the filament) but I am not sure if there would be degraded lamp life from it or not.hi Uber,
Interesting effect, if its correct.
Regards
It sounds plausible, since that is what the halogen cycle does (redeposits vaporized carbon onto the filament) but I am not sure if there would be degraded lamp life from it or not.
Doing that repetitively might leave weak spots in the filament that would not be there otherwise. I suppose you would have to ask a mfg apps guy that one.
If the voltage is 230VAC and the mains frequency is 50Hz then this triac should be warm driving only 1kW. it has a current rating of 40A but you are using only 4.3A.Can anyone help me ?,
brothers i am using traic BTA41 for element dimmer of 1KW. I am using its driver MOC3021 it works well but after some time it becomes heats up, i have added a big heat sink and i am using it in closed envoirnament, its temperature goes up than 100 deg c. what should i do?
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