How to control the brightness of a light bulb?
How to control the brightness of a light bulb? If it is DC, give the triode PWM wave selection to control its brightness.
But what if it’s AC? For example, the 220 volt 50 Hz alternating current in our home is obviously not suitable to use a triode at this time, because the voltage of the alternating current is constantly changing, and the triode cannot work normally at all. In addition, the voltage of the alternating current is too high, and generally a triode cannot withstand it. Such a large voltage.
Is there any way to control the brightness of this light? Of course, there is, that is, thyristors, which are very important. AC control devices, such as adjusting the brightness of AC lights, adjusting the water temperature of electric kettles, and stepless speed regulation of fans, can all be implemented with thyristors.
Next, let's talk about how the thyristor adjusts the brightness of the light bulb. Before we talk about it, we need to understand how to control the opening and closing of the thyristor.
This is an ordinary thyristor. When we give the G electrode an appropriate voltage, it will conduct. However, if the voltage is removed at this time, it cannot cut off. To make it cut off, we only need to remove the power supply voltage and use the thyristor. With this characteristic, you can use it in AC light adjustment.
This is the AC dimming circuit of the thyristor. We only need to turn the sliding rheostat to adjust the brightness of the bulb and the waveform of the power supply. When the alternating current increases to point A, through the voltage division of the rheostat R2 and R1, the voltage output by R2 at this time is just right. When the thyristor is turned on, the bulb is lit. After that, the bulb will continue to light up until point E, when the AC voltage drops to zero, the thyristor is cut off, and the bulb goes out again.
Then when the next point A comes, the light bulb is lit again. During this process, the waveform on the small light bulb is like this, but because the frequency of the alternating current is very fast, we can hardly see its flicker. If we want the light bulb to For higher brightness, the sliding rheostat R2 can be adjusted upward, so that the voltage output by R2 will be larger.
Before the alternating current reaches point A, the thyristor turns on at point B. Then, in the same process as above, when the alternating current reaches point E, the thyristor will turn off again, and so on. The waveform falling on the small light bulb at this time is like this, you can It can be seen that their waveforms are similar, but the conduction time after adjustment is obviously longer than before.
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