linear voltage regulator

linear voltage regulators use an active pass element to reduce the input voltage to the regulated output voltage. Some devices use bipolar transistors and others use metal-oxide semiconductor field effect transistors (MOSFETS). The use of voltage-controlled sources enables IC linear voltage regulators to force a fixed voltage to appear at the output terminal. Control circuitry monitors the output voltage and adjusts the current source accordingly. Generally, the control circuitry contains a pass device such as pair of NPN transistors driven by a PNP transistor. NPN transistors contain a P region between two N regions. PNP transistors contain an N region between two P regions.

For IC linear voltage regulators, the regulator type determines the configuration of the pass device as well as the dropout voltage, the voltage at which the output falls out of regulation. Standard voltage regulators use an NPN Darlington configuration and have a dropout voltage between 1.5V and 2.2 V. Low dropout (LDO) regulators differ from standard regulators in that the pass device consists of a single PNP transistor. The dropout voltage equals the voltage across the PNP transistor and ranges from 100 mV to 300 mV. Quasi-LDOs are similar to standard regulators, but use NPN and PNP transistors as the pass device. Dropout voltages for quasi-LDOs are higher than for LDOs, but lower than for standard regulators.

In addition to the dropout voltage, IC linear voltage regulators include performance specifications such as the input current and the output current, both of which are expressed in continuous mode (DC). Input currents and output currents are voltages applied to ICs at both minimum and maximum levels. Another measurement, the voltage-out tolerance, represents the tolerance in plus and minus values of the principal output voltage. The voltage-out tolerance indicates how often IC linear voltage regulators can output regulated voltages that remain within a given range. The quiescent current, also known as the operating current or ground current, flows from the battery to power the regulator but does not reach the load itself.

IC linear voltage regulators can provide positive, negative, or both positive and negative polarity. With positive polarity, the output voltage is in phase (positive) with the input voltage. With negative polarity, the output voltage is out of phase (negative) with the input voltage. Reverse voltage protection prevents damage to regulators if the input voltage is reversed. Input overcurrent protection protects regulators if excessive input current is applied. The output voltage type determines whether the output voltage is fixed or can be adjusted within a specified range. IC linear voltage regulators with an internal current limit control the amount of current produced. Some regulators have a single output while others have multiple outputs. Error flags are available to indicate when an output has dropped below a percentage of its nominal value.

IC linear voltage regulators are available in a variety of package types and life stage levels. They are used in industrial, automotive, aerospace, and military applications, as well as in consumer electronics and telecommunications.


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