Transformer is a magnetic circuit whose name is derived from its ability to transform (i.e. change) the magnitude of an AC voltage applied to it
Construction of Multi-voltage transformer
So we can say that multi-voltages may be included in secondary that depends upon our requirements. For this purpose, a number of secondary windings are used as the secondary. The voltages induced that we want depends upon the number of turns. The current requirement is achieved by the diameter of the coil used.
Multi-voltage supplies circuit is shown in figure. The main component is a multi-voltage transformer which has one primary winding and a number of secondary windings. When alternating current passes through primary winding then alternating flax will be induced this induces e.m.f in the secondary. Since there are a number of secondary windings hence a number of voltages will be induced. The magnitude of the induced voltages depends upon the number of turns. More the number of turns, more flux cuts this secondary and more voltages will be induced. Less number of turns, less flux cuts this seconding winding and fewer voltages will be induced. So we can say that induced voltages in the secondary are directly proportional to the number of turns in the secondary. The current requirement is handled by the thickness of the secondary windings.
As shown in figure, in the upper winding, 20 Vrms a.c. voltages are induced which are then rectified by a single diode 1N2070. Then a low-pass T-type filter is used for filtration of the rectified output. This rectified and filtered voltages are then regulated by a zener IN4749, hence +24V dc is obtained.
In the second winding negative voltages will be induced in the tapped connection. Which is then regulated by transistor in the third winding the positive voltages will be induced in the tapped connection which is then filtered by a low pass filter and +100 voltages are obtained. In the last winding fewer voltages are produced.