Designing Embedded Hardware, 2nd Edition

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 devices such 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 and sampling in Chapter 13.) Therefore, we need a voltage regulator 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 supply. If your system is operating from a battery, the varying current draw of your computer 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 since it provides a constant output. Including a voltage regulator in your design is good practice.

Tip

National Semiconductor has a good online tutorial on using and designing voltage-regulator circuits based on their chips. It can be found at ...