220V AC Voltage regulator, controlled with micro controller?


I'm fairly new to Arduino (I'm actually using Netduino), and I have been puzzling with making a voltage regulator, for a 100W lightbulb. But my issue is, that I would like to control it digitally, with a micro controller - and not with the usual potentiometer.

Is there some kind of digital potentiometer I could use, or create?
Or better yet, instructables on doing something similar to this? I've been looking, but all seems to be manually operated, and most of them are for low voltage DC.

I'm pretty new to electronics as well, and I definitely would prefer, to NOT burn down the house.

Any advice, comments and links are much appreciated :)

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Look for circuits using OPTO-ISOLATED TRIACS, like the MOC3010 or MOC3050. They need an EXTRA, bigger Triac to work a real load.

goehler_dk (author)  steveastrouk2 years ago

I see I have some research to do, before I can fully appreciate your answer.

But just to make sure, I have to ask: Will this allow me to regulate the Voltage for my lightbulb, thus enabling me to turn the light intensity up and down, with a digital signal?

Yes, although actually its adjusting the maximum power into the bulb, the maximum voltage will be fixed, but not on as long.

goehler_dk (author)  steveastrouk2 years ago

Okay, so I'm varying the Amps? :) Sorry for my illiteracy - I'm working on it :)

In the olden days, huge POTs were used to control the brightness of a light, they were called rheostats. They dissipated and wasted a LOT of power, and were expensive because they were difficult to design in such a way that they won't burn the house down, so solids state technology has replaced them.

The reason they were inefficient is because they limited current by adding resistance to the circuit, making it more difficult for electrons to force their way through it, causing a voltage drop to develop across the rheostat, so less voltage got to the bulb, and consequently because the lamp could not draw as much current or power, and it got dimmer.

Another old way to do it was to use a autotransformer, and although this is very efficient, variacs are big and $$$ too. (a autotransformer is a special type of transformer with a single coil with a wiper that can continuously wipe across the coil and select how much the voltage will be stepped down)

finally, the way modern small dimmers work is by essentially chopping parts of the AC waveform away so less average power will reach the bulb. (it works sort of like PWM) This works well for simple incandescent lamps, but many CFLs and LED lights as well motorized things do NOT like this choppy waveform, and will act weird and cause problems.

You're varying where the voltage is turned ON. The total area under the graph of voltage is proportional to the bulb power.


Hope my 40 Amp meets a real load :)

I've seen people driving bulbs direct, hence the comment about additional triacs

Yea, they only survive inrush when accidentally switched at zero crossing !

-max-2 years ago

If you already have a circuit that uses a potentiometer, you might be able to retrofit a digital pot in it's place, and if the 2 connectors other than the wiper are connected across a low voltage source and ground, you may be able to get away with using just a simple DAC.

If you are designing it from scratch, then you will definitely want a triac (they work well with AC, unlike many other types of transistors, but have the downfall that once it is triggered, it stays tached on until the AC reverses direction or goes to 0V.). as well as a way to trigger the triac, that must be galvanically (fancy word for electrically) oscillated from the micro, so the design isn't simple. The most common way to do that is to have digital output of a microchip power the LED side of an opto-coupler (basically an LED with a light sensor glued to it, basicly) and the output of the opto-coupler will have to be set up to drive the gate of the TRIAC. That way a positive pulse from the micro will trigger and latch the triac onto it's ON position and allow power to flow into a load until the AC reverses polarity.

By Controlling how late that pulse is given from the micro, we can control how long that the AC will flow through the triac and into the load before the AC reverses direction and switches the TRIAC back off. In order for the micro to "know" the phase of the AC, and when it will be reversing voltage and passing the 0V point, we can capacitively couple a long insulated wire tapped along the live AC wire, or use a small transformer that steps down the voltage to less than 5V and feeds into the analog input of the microchip). Then once a point where 0V is detected,

It will probably be easier to use something like a servo motor to control the position of a dimmer switch. All the difficult electronics are already taken care of and UL listed.

iceng2 years ago

Use a triac driven by an opto-isolator which is driven by a 5V microprocessor that has an AC line synch to aid in power phase timing the lamp.

You can replace the pot with an UP / DOWN Button or a 555 for reference.