We have AC loads all around us. And most household appliances are powered by 220 V AC. There are a lot of situations that we want to have full control over an AC load like controlling the light of a lamp, controlling the speed of the AC motor / fan, controlling the vacuum cleaner and so many more. applications. The correct way to control the variation of 220 V AC is by phase control with a Triac.
But controlling an AC load is not as simple as controlling a DC load. The electronic circuit for these two applications is different. The AC mains with a sine wave has the frequency of 50Hz. To build an AC dimmer, zero crossing points (the points where the wave changes polarity) are important. To detect these points, we must first build a zero crossing detector. Likewise, we need to control the phase and cycle of the waveform. Since each component cannot tolerate 220V AC, we therefore have to isolate the circuit from 220V AC using another component called an opto-isolator.
The circuit is divided into 4 parts:
1.Zero detection circuit
2.Phase / angle control using Triac
3.Circuit to control dimming
4.Delay angle display circuit
1. Zero detection circuit
The AC voltage we get from home power is around 311 volts peak to peak or 230V RMS. The frequency is usually equal to 50 Hz. We have a positive and a negative part, so there will be a zero crossing. We will therefore have to detect this zero crossing because our pulse must be in phase with the alternating voltage.
So, we have to detect when the voltage goes from positive to negative or from negative to positive and synchronize our pulse with it so that it always fires in the same place.
2. Phase / angle control using Triac
The TRIAC will remain disabled until it receives a trigger pulse.
Once received, it will remain on until the main input changes polarity.We must first detect the zero crossing because the pulse must be in phase with the AC voltage. So, we have to detect when the voltage goes from positive to negative or from negative to positive and synchronize our impulse with it so that it always fires in the same place.
3. Circuit to control dimming
To control the power all we have to do is control the time between zero crossing and when we trigger the pulse at the TRIAC gate. We are therefore going to use a potentiometer to modify the delay time.
4. Delay angle display circuit
To display the value of the delay angle we will use an LM016L type LCD display
5. The simulation
- For α = 3π / 4
- For α = π / 4
- For α = π / 8
- For α = π / 2
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