Power supply is a broad term but this lesson is restricted to discussion of circuits that generate a fixed or controllable magnitude dc voltage from the available form of input voltage. Integratedcircuit (IC) chips used in the electronic circuits need standard dc voltage of fixed magnitude. Many of these circuits need well-regulated dc supply for their proper operation. In majority of the cases the required voltages are of magnitudes varying between -9 to +9 volts. Some equipment may need multiple output power supplies. For example, in a Personal Computer one may need 3.3 volt, ±5 volt and ±9 volt power supplies. The digital ICs may need 3.3volt supply and the hard disk driver or the floppy driver may need ±5 and ±9 volts supplies. The individual output voltages from the multiple output power supply may have different current ratings and different voltage regulation requirements. Almost invariably these outputs are isolated dc.voltages where the dc output is ohmically isolated from the input supply.

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