Introduction
All electronic systems require a source of power. In almost all cases the voltage and current values are
specified. The current value is in amperes as a load on the supply, and the voltage value is to be held within a specified tolerance (usually a percentage of the nominal value) as the current value varies within specified limits as the load changes. The nominal value of voltage times the nominal value of current determines the watts of power required of the supply. In this chapter, not only will the source of the voltages and their regulation be discussed, but the way the supply voltages are distributed throughout a system. In addition, the sophisticated circuits that are now available to monitor, detect and protect systems from damage, errors and failure will be discussed.
AC to DC Power Supplies :
Figure 9-1a shows a general AC to DC power supply. Its source is the alternating current voltage of
120VAC or 250VAC, 60 Hz that is distributed commercially by the local power company. The alternating
voltage varying plus and minus around zero is rectified into voltages that vary only above zero. The half-alterations are passed through a filter that produces a DC voltage of designed amplitude. A small ripple
voltage results from the amount of filtering compared to the input voltage variations. The ripple is superimposed on the DC voltage and represents a so-called noise. Because the output voltage must be controlled accurately within tight tolerances, a voltage regulator (or it could be a current regulator) is required. The voltage is held to within 1% to 10% of VOUT over the specified load current and its changes depending on the application and type of regulator. Many AC to DC power supplies must be isolated from the incoming AC line. Figure 9-1b shows such a design using a full-wave rectifier and transformer isolation. If the power supply need not be isolated, Figure 9-1c shows a design using a bridge rectifier supplied directly from the AC line.
All electronic systems require a source of power. In almost all cases the voltage and current values are
specified. The current value is in amperes as a load on the supply, and the voltage value is to be held within a specified tolerance (usually a percentage of the nominal value) as the current value varies within specified limits as the load changes. The nominal value of voltage times the nominal value of current determines the watts of power required of the supply. In this chapter, not only will the source of the voltages and their regulation be discussed, but the way the supply voltages are distributed throughout a system. In addition, the sophisticated circuits that are now available to monitor, detect and protect systems from damage, errors and failure will be discussed.
AC to DC Power Supplies :
Figure 9-1a shows a general AC to DC power supply. Its source is the alternating current voltage of
120VAC or 250VAC, 60 Hz that is distributed commercially by the local power company. The alternating
voltage varying plus and minus around zero is rectified into voltages that vary only above zero. The half-alterations are passed through a filter that produces a DC voltage of designed amplitude. A small ripple
voltage results from the amount of filtering compared to the input voltage variations. The ripple is superimposed on the DC voltage and represents a so-called noise. Because the output voltage must be controlled accurately within tight tolerances, a voltage regulator (or it could be a current regulator) is required. The voltage is held to within 1% to 10% of VOUT over the specified load current and its changes depending on the application and type of regulator. Many AC to DC power supplies must be isolated from the incoming AC line. Figure 9-1b shows such a design using a full-wave rectifier and transformer isolation. If the power supply need not be isolated, Figure 9-1c shows a design using a bridge rectifier supplied directly from the AC line.
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