Lm317 Adjustable Voltage Regulator

Topics: Resistor, Electronic component, Voltage divider Pages: 4 (918 words) Published: November 20, 2012
Research about LM317 Positive Adjustable Linear Voltage Regulator: The LM317T is a 3-terminal integrated circuit which can supply a load current of up to 1.5 Amps with an output voltage of between 1.2V and 37 Volts. It accepts an input voltage of between 3 and 40 volts. It can be used to regulate either current or voltage in situations where a fixed current or fixed voltage is required. The level of current or voltage required can be adjusted by connecting the chip in series with a fixed resistor and a potentiometer. The LM317 is also a popular variable voltage regulator. It was invented by Robert C. Dobkin and Robert J. Widlar in 1970 while they worked at National Semiconductor. Furthermore, both line and load regulation is better than standard fixed regulators. In addition to having higher performance than fixed regulators, this device includes on-chip current limiting, thermal overload protection, and safe operating-area protection. All overload protection remains fully functional, even if the adjust terminal is disconnected. The LM317 is versatile in its applications, including uses in programmable output regulation and local on-card regulation. Or, by connecting a fixed resistor between the adjust and output terminals, the LM317 can function as a precision current regulator. An optional output capacitor can be added to improve transient response. The adjust terminal can be bypassed to achieve very high ripple-rejection ratios, which are difficult to achieve with standard three-terminal regulators.

LM317 Adjustable Voltage Regulator pin configuration.

LM317 Adjustable Voltage Regulator Internal Block Diagram

Operation of the LM317 Adjustable Voltage Regulator:
A constant 1.25V reference voltage (VREF) produces a constant current (IREF) through R1 regardless of the value of R2. IREF = VREF / R1
In operation, the LM317 develops a nominal 1.25V reference voltage, VREF, between the output and adjustment terminal. The...
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