The IC is capable of delivering up to 1A of output current. Input voltage can be up to 40V and output voltage can be adjusted from 1. Typical positive voltage regulator circuit using LM Input voltage is fed to the pin3 v in of the IC and regulated output voltage is available from pin 2 V out of the IC.

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LM 1. They are designed to supply more than 1. The nominal output voltage is selected by means of only a resistive divider, making the device exceptionally easy to use and eliminating the stocking of many fixed regulators.

Vo Line Regulation? Input-output Differential Voltage. Figure 2 : Dropout Voltage vs. Junction Temperature. Figure 3 : Reference Voltage vs. Junction Figure 4 : Basic Adjustable Regulator. This is used to set a constant current flow across an external resistor divider see fig.

A max and to maintain it very constant with line and load changes. Usually, the error term IADJ? R2 can be neglected. To obtain the previous requirement, all the regulator quiescent current is returned to the output terminal, imposing a minimum load current condition.

If the load is insufficient, the output voltage will rise. Furthermore, programmable regulator are easily obtainable and, by connecting a fixed resistor between the adjustment and output, the device can be used as a precision current regulator. In order to optimise the load regulation, the current set resistor R1 see fig.

Performance may be improved with added capacitance as follow: An input bypass capacitor of 0. F An adjustment terminal to ground 10? F tantalium or 25? FAluminium electrolitic capacitor on the output to improve transient response. In additional to external capacitors, it is good practice to add protection diodes, as shown in fig. D1 protect the device against input short circuit, while D2 protect against output short circuit for capacitance discharging.

Figure 5 : Voltage Regulator with Protection Diodes. D1 protect the device against input short circuit, while D2 protects against output short circuit for capacitors discharging Figure 6 : Slow Turn-on 15V Regulator.

Figure 7 : Current Regulator. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use.

No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specification mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied.

STMicroelectronics products are not authorized for use as critical components in life support devices or systems withoutexpress written approval of STMicroelectronics.



Linear regulators inherently waste power; the power dissipated is the current passed multiplied by the voltage difference between input and output. A LM commonly requires a heat sink to prevent the operating temperature from rising too high. For large voltage differences, the power lost as heat can ultimately be greater than that provided to the circuit. This is the tradeoff for using linear regulators, which are a simple way to provide a stable voltage with few additional components.

AS 1668.1 PDF

LM317K STMicroelectronics, LM317K Datasheet



Few LM317 voltage regulator circuits


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