When the power source is an ac voltage, the transformer. Rectifier, and input filter design are as important as the regulator design itself for optimum system performances. This section presents input supply and filter design information for designing a basic capacitor input supply.
The input supply consists of three basic sections: (I) input transformer, (2) rectifier, and (3) filter as illustrated in Figure 5-42.
The first two sections, the transformer and the rectifier, are partially dependent upon each other because the structure of one depends upon that of the other. The most common transformer configurations and their associated rectifier circuits are illustrated in Figure 5-43.
The particular configuration used depends upon the application. The half-wave circuit [Figure 5-3(a)] is used in low-current applications. This is because the single rectifier diode experiences the total load current and its conversion efficiency is less than 50%. The full-wave configurations [Figures 5-43(b) and 5-43(c)] are used for higher current applications. The characteristic output voltage waveforms of these configurations are illustrated in Figure 5-44.
Before the input supply and its associated filter can be designed, the voltage, current, and ripple requirements of its load must be fully defined. The load, as far as the input supply is concerned, is the regulator circuit. Therefore, the input requirements of the regulator itself become the governing conditions.
Because the input requirements of the regulator control circuit govern the input supply and filter design, it is easiest to work backwards from the load to the transformer primary.