ElectroMaster

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).

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lobitoferoz

thanks for the circuit ,excellente'''

Hero999

You don't need an opto-isolator or a bridge rectifier though.

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kumyanski

I need the full detail for knowlegde gaining

kumyanski

I need the full detail for knowlegde gaining

Hero999

WTF does that mean?

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shokjok

You may want to add a resistor off the diode bridge, to save the zener diode and yourself from injury. I've tried a similar circuit as an extension phone ringer, to flash an LED or buzzer.

Leftyretro

Knowlege gaining is best obtained by individual study, research and experiance. Asking to be spoon fed such information will just further prevent you from being able to work out future knowlege on your own. There is nothing used in this circuit that would not be learned by the normal study and experiance in electronics circuits and components.

It's kind of the give a man a fish and feed him for a day, teach him to fish and he is fed for life....or something like that

A better question you might ask is how best to learn knowlege of electronics such that the above circuit would be understandable to me.

Lefty

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pohchinpoh

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?

Attached Images

triac circuit.JPG (13.0 KB, 8 views)

ericgibbs

hi,
Driving the Triac with a pulse generator in order to switch 'ac' will give a flickering/flashing light or it be on constantly.

It will not control the brightness/intensity of the light.

EDIT:
To control the brightness, you need to change the trigger point within the mains cycle, at which the Triac is triggered.

Look here:
Light Dimmer Circuit Using A Triac

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audioguru

The micro-controller needs to be sync'd to the mains frequency to enable it to trigger the triac early for each mains pulse for bright lights, or trigger the triac late for each mains pulse for dim lights. That is how a light dimmer works.

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