Single Phase Variable Voltage Generation using Keyboard & Microcontroller
Normally a single phase voltage is varied by analog methods such as dimmer but we cannot get exact voltage by dimmer also. To achieve smart/exact voltage level VFD drives are used. To vary voltage by changing the firing angle of thyristor a variable ac voltage can be obtained. Thyristor conducts in both cycles of ac. If conduction angle is controlled by firing angle of thyristor. For half ac cycle firing angle changes from 0 degree to 180 degree according to that conduction angle changes. As conduction angle and firing angle are inversely proportional to each other. Means that if firing angle less then conduction angle is more and vice versa. A zero crossing detector circuit is used to know the zero point of ac. when zero crossing section gives output of logic 1 then from this point ac voltage starts to rise/fall. This is the reference point from that point to maximum 180 degree point firing angle can be controlled. In this way a variable output voltage is generated.
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