LM317T Voltage Regulator: Functions, Usage, Applications and LM317T vs LM317
22 January 2024
Ⅱ. What functions does LM317T have?
Ⅲ. Technical parameters of LM317T voltage regulator
Ⅳ. Circuit of LM317T voltage regulator
Ⅴ. What is the difference between LM317T and LM317?
Ⅵ. How to use LM317T voltage regulator?
Ⅶ. Applications of LM317T voltage regulator
LM317T is a three-terminal adjustable positive voltage regulator that can achieve stable voltage output. The device has good linearity, load regulation and temperature stability to meet the needs of most circuits. Since the LM317T can control the output voltage through external components, it is especially suitable for situations where rapid voltage adjustment is required. This article will introduce the LM317T to help you better apply this device.
The LM317T is a forward adjustable voltage regulator designed to supply load currents in excess of 1.5 A. Its output voltage is adjustable from 1.2 to 37 V, and the nominal output voltage is simply selected via a resistor divider. This makes the device easy to use and eliminates the hassle of installing a fixed voltage regulator. LM317T linear voltage regulators are very robust as they feature internal current limiting and thermal shutdown. This adjustable voltage regulator is available in various packages for TO220, TO220FP and D2PAK devices.
Alternatives and equivalents:
• B29150
• LM317TG
• LM217T
• LM317P
• Various packages: It can choose TO-220, TO-3 and other package forms to meet the needs of different application scenarios.
• Temperature protection: It has built-in temperature protection feature. This protection mechanism automatically cuts off the output in the event of overheating, thus protecting the regulator from damage.
• Good stability: LM317T has a high gain bandwidth product and excellent frequency response characteristics, and can achieve high-precision voltage stable output.
• Wide adjustment range: LM317T can easily adjust the output voltage through external resistors. The extensive adjustment range caters to diverse application scenarios, excelling in circuits demanding precise voltage control or situations necessitating flexibility in adapting to various power supply voltages.
• Overload protection: LM317T has overload protection function. This regulator adopts advanced short-circuit protection technology, which can automatically cut off the output when the output is short-circuited or overloaded, thereby effectively protecting the load and voltage regulator.
The following is how the LM317T regulator looks when it is connected to the circuit so that it provides a constant DC voltage output.
In this circuit setup, the DC voltage supply is connected to the VIN pin of the regulator. This particular pin is designed to accept the input voltage, after which the chip initiates a downward regulation process. It's crucial to note that the voltage applied to this pin should surpass the voltage it produces. Voltage regulators function solely to control voltage levels and are incapable of generating voltage independently. Thus, to achieve a desired output voltage, VOUT, the input voltage, VIN, must exceed VOUT. For our circuit, a stable 5VDC output is required, necessitating an input voltage higher than 5 volts. Typically, in voltage regulators, the input voltage is maintained approximately 2 volts above the regulator, unless a low voltage differential regulator is utilized. In our case, with a 5-volt output target, we supply 7 volts to the regulator.
Now that we have dealt with the input pin, in addition we must deal with the adjustable pin (Adj). This is the pin that allows the voltage to be adjusted to the level we want. Since we want to output 5 volts, we must calculate which value of R2 will produce a 5 volt output. We use the output voltage formula, VOUT = 1.25V (1÷R2/R1). Since R1 = 240Ω, the equation is 5V = 1.25V (1 + R2/240Ω), so R2 = 720Ω. Therefore, when the value of R2 is 720Ω, if an input voltage greater than 5 volts is fed in, the LM317T will output 5V. The last pin of the LM317T is the output pin. This is where the regulated voltage (in this case 5 volts) will appear. In order to supply the circuit with the regulated 5 volts, we now simply connect it to the output pin.
The LM317T is a voltage regulator based on a tension regulator design, while the LM317 is a three-terminal voltage regulator. The LM317T has a higher maximum current output capability (typically 1.5A), operates in a higher input voltage range (typically 40V), and has better linearity and temperature stability. In comparison, the LM317 has a lower input operating voltage range, usually below 35V. Its maximum output current is also small, only about 1A.
When using LM317T, we should pay attention to the following aspects:
1. Thermal management: Since the LM317T generates heat when working, we need to take appropriate thermal management measures. To lower the temperature, we can attach a heat sink to the bottom of the LM317T and make sure the surrounding environment is well ventilated. In addition, we should also check the temperature of the equipment regularly to ensure that it is working within a safe range.
2. Circuit connection: The circuit connection of LM317T is relatively simple. Typically, we need to connect its input to the power supply, its output to the device you want to regulate, and the adjustment terminal (also called "adj" or "SET") to ground through an appropriate resistor.
3. Current limit: The LM317T has a built-in current limit function to protect the device from overload current. By default, the maximum output current is 1.5A, but it can be adjusted as needed. To adjust the maximum current, we need to adjust the current flowing through the adjustment terminal, which can be achieved by changing the resistance value of R1.
4. Voltage adjustment: Voltage adjustment is realized by changing the resistor on the adjustment terminal (usually marked as "SET" or "Adj"). We need to use an appropriate resistor (usually between 200 ohms and 1 megohm) to control the output voltage. The output voltage can be calculated by the following formula: Vout = 1.25 * (R1 + R2) / R1. where R1 is the resistor input to the adjuster and R2 is the feedback resistor (usually 10K ohms).
5. Protective measures: In order to protect the LM317T from potential hazards such as overvoltage, overcurrent and overheating, we should take a series of protective measures. For example, we can add protection circuits to limit input and output voltages, as well as use temperature sensors to monitor chip temperature. In addition, we should perform regular maintenance and inspection to ensure that the device works properly.
Due to its excellent performance and characteristics, LM317T is widely used in many fields. Some common application scenarios are listed below:
• Power supply filtering: LM317T can be used as part of the power supply circuit to provide a stable power supply voltage, and to a certain extent, the power supply fluctuation filtering to ensure the stability of the power supply.
• Battery charger: The LM317T can be used to design a simple battery charger circuit. By controlling the output voltage and current, it enables safe and effective charging of different types of batteries. For users, using the LM317T to design battery charger circuits can eliminate a lot of tedious steps, such as adjusting resistor values and measuring the battery's state of charge.
• Current regulator: The LM317T can also be used as a current regulator. By inserting a current sense resistor between the adjusting resistor and the output, we can make the LM317T provide a stable current at the output.
• Voltage reference source: Because its output voltage has high stability and accuracy, it can be widely used as a voltage reference source in various circuits. As a voltage reference source, LM317T can provide an accurate reference voltage for other circuits to ensure the normal operation of the circuit.
• Fixed output voltage regulator: LM317T can also be used to realize fixed output voltage regulator. By choosing the right resistor value, we can configure the LM317T to output a specific voltage, such as 5V, 9V, etc.
• Wireless communication equipment: Since LM317T can provide stable voltage output, it is often used in wireless communication equipment to ensure the normal operation of RF circuits and other critical parts.
• Adjustable voltage regulators: The most common use of the LM317T is as an adjustable voltage regulator. It stabilizes the input DC voltage and outputs it as a fixed DC voltage. When using LM317T, we need to set the output voltage of LM317T by connecting resistors and adjusting resistors.
Frequently Asked Questions
1. What is the maximum voltage of LM317T?
The LM317 device is an adjustable three-terminal positive-voltage regulator capable of supplying more than 1.5 A over an output-voltage range of 1.25 V to 37 V.
2. What is the difference between LM317 and LM317T?
There is no functional difference as they are one in the same. The T at the end just indicates that it's in a TO-220 package.
3. What is the use of LM317T?
The LM317 serves a wide variety of applications including local, on card regulation. This device can also be used to make a programmable output regulator, or by connecting a fixed resistor between the adjustment and output, the LM317 can be used as a precision current regulator.
4. What is the difference between LM317T and 7805?
LM317 is an adjustable voltage regulator, while LM7805 is the constant voltage regulator. LM317 can give an adjustable output voltage in the range of 1.5V to 37V, whereas LM7805 can only give an output voltage of 5V.
5. What is the difference between LM317T and 7805?
LM317 is an adjustable voltage regulator, while LM7805 is the constant voltage regulator. LM317 can give an adjustable output voltage in the range of 1.5V to 37V, whereas LM7805 can only give an output voltage of 5V.
