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Designing Embedded Hardware by John Catsoulis

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Regulators

A voltage regulator is a semiconductor device that converts an input DC voltage (usually a range of input voltages) to a fixed-output DC voltage. They are used to provide a constant supply voltage within a system.

While many components in an embedded system can operate from a wide power-supply range, a fixed operating voltage is necessary for such devices as Analog-Digital Converters (ADCs), since many use the internal power supply as a reference. In other words, the output voltage of a sensor is sampled as a percentage of the voltage supply of the ADC. If the supply is not a known voltage, then any sampling performed by the ADC is meaningless. (We’ll look at ADCs in Chapter 12.)

Therefore, a voltage regulator is required to provide a constant voltage source and, thereby, a constant voltage reference. Further, a voltage regulator can assist in removing power-supply noise and can provide a degree of protection and isolation for the embedded system from the external power source. If your system is operating from a battery, the varying current draw of your system can combine with the battery’s internal resistance to create a varying supply voltage. The addition of a voltage regulator prevents this from becoming a problem to your embedded system. Including a voltage regulator in your design is good practice. National Semiconductor has a good online tutorial on using and designing voltage regulator circuits. It can be found at http://www.national.com/appinfo/power/webench ...

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