Lm317 Adjustable Voltage Regulator

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. 5V 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 reference voltage is impressed across the resistor R1 and, since the voltage is constant, a constant current I1 then flow through the output set resistor R2, giving an output voltage of: VOUT = VREF (1+ R2/R1) + IADJ R2 (The IADJ is typically a 50 µA; it is negligible in most applications and the input voltage should be 2-3V higher than with its output voltage. Application Information: NOTES: A. Ci is not required, but is recommended, particularly if the regulator is not in close proximity to the power-supply filter capacitors. A 0. 1-? F disc or 1-? F tantalum provides sufficient bypassing for most applications, especially when adjustment and output capacitors are used. B. CO improves transient response, but is not needed for stability. C. The Output Voltage (Because IAdj typically is 50 ? A, it is negligible in most applications. ) D. CADJ is used to improve ripple rejection; it prevents amplification of the ripple as the output voltage is adjusted higher.

If CADJ is used, it is best to include protection diodes. E. If the input is shorted to ground during a fault condition, protection diodes provide measures to prevent the possibility of external capacitors discharging through low-impedance paths in the IC. By providing low-impedance discharge paths for CO and CADJ, respectively, D1 and D2 prevent the capacitors from discharging into the output of the regulator. Schematic Diagram: Solving for IREF: IREF = VREF / R1 IREF = 1. 25V / 10000? IREF = 125mA Solving for VOUT(MIN) and VOUT(MAX):

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VOUT (MIN)/(MAX) = VREF (1+ R2/R1) + IADJ R2 VOUT(MIN) = 1. 25V (1+ 0? /10000? ) + 0. 000050A * 0? VOUT(MIN) = 1. 25V VOUT(MAX) = 1. 25V (1+ 50000? /10000? ) + 0. 000050A * 50000? VOUT(MAX) = 10V (Therefore, the minimum input voltage that in order to supply its maximum output voltage is 12V. ) List of Components: Name| Type| Symbol| Material| Description| LM317 (IC) | Adjustable Linear Voltage Regulator| | | It is an adjustable three-terminal positive voltage regulator capable of supplying more than 1. 5A over an output-voltage range of 1. 5 V to 37 V. | Potentiometer| Variable Resistor| | | Informally, a pot, in electronics technology is a component, a three-terminal resistor with a sliding contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat. | Ceramic Capacitor| Unpolarized| | | It is a two-terminal non-polar device that is constructed of alternating layers of metal and ceramic, with the ceramic material acting as the dielectric. | Name| Type| Symbol| Material| Description|

Electrolytic capacitor| Polarized| | | Formerly known as condenser, is a passive two-terminal electrical component used to store energy in an electric field. | Resistor| Carbon Film| | | It is a passive two-terminal electrical component that implements electrical resistance as a circuit element. The current through a resistor is in direct proportion to the voltage across the resistor’s terminals. | Diode| Rectifier| | | It is a two-terminal electronic components that allow current to flow in only one direction, from an anode (+) to a cathode (-), and that convert AC to DC. Component Layout: PCB Design Layout: Conclusion: I observed that the output voltage of the regulator (LM317) is depend on the R1 and R2 because when the R2 is set to minimum output resistance, the output voltage decrease to its minimum value that is equal to the voltage reference (VREF) while it is set to the maximum resistance, its output voltage will increase and it will reach its maximum output voltage that it can supply. As I said, that the output voltage can control and set it to the value that you desired or enough to supply a load or a circuit.

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