What is LM350 Adjustable Voltage Regulator

The LM350 IC is an adaptable positive voltage regulator. It has three terminals like Vin, Vout and Adj. This kind of regulator is used to supply an extra 3 amperes current over an output range. This IC is extremely simple to utilize and needs simply two exterior resistors to fix the output voltage. In advance, it uses current limiting internally, compensation of safe area, thermal shutdown, etc. This regulator is used in a variety of applications like local and on-card regulation. By using this regulator we can design a programmable o/p regulator, an adjustable switching regulator otherwise it is used as a precision current regulator by using a fixed resistor among the two pins like adjustment & output.

LM350 IC Pin Configuration

The pin configuration of this IC is discussed below.

  • Pin1 (Adjust): This pin is used to adjust the o/p voltage.
  • Pin2 (Vout/Output Voltage): The regulated o/p voltage can be fixed using the adjust pin and thus can be attained from the Vout pin.
  • Pin3 (Vin/Input Voltage): The i/p voltage which we want to regulate is given to this pin


The features of this integrated circuit include the following.

  • The output current is 3.0 A
  •  Output can be changed between 1.2 V & 33 V
  • Typical load regulation is 0.1%
  • Line regulation is 0.005%/V
  • The protection of internal thermal from overload
  • Safe area compensation of output transistor
  • For high voltage applications, the operation will be floating.
  • Standard 3 terminal transistor package
  • It removes stored fixed voltages
  • Junction temperature operating range is 125°C
  • This IC is accessible in different packages like To-220, TO263, and SOT223,
  • Alternative and Equivalent LM350 Voltage Regulators
  • The alternative voltage regulators are like LM7805, 7806, 7809, 7812, 7905, 7912, 117V33, and XC6206P332MR.
  • The equivalent voltage regulators are like LM317, 1117, LT1086, PB137, and LM337.

Where to use LM350?

For changeable voltage regulation necessities, this regulator would be the primary choice. Because this IC offers up to 3A, so if we want to supply more than 1.5A then we can employ the LM350 IC. If you want to fix voltage between from 1.25V – 33V & to supply current up to 3A then a variable voltage regulator is used. This regulator is a good choice for different applications. Apart from that, this regulator includes a current regulator that is used in battery charging applications.


LM350 IC Circuit Diagram

The circuit diagram of the LM350 IC is shown below. It is a three-terminal integrated circuit. This regulator is used in a wide range of applications. And it can be used as a variable voltage regulator.


Already we have discussed that this IC includes three pins where the input voltage is given to Vin pin. After that, a potential divider is used to fix a voltage at the adjust pin. Here the voltage divider can be formed using a pair of resistors. So that output voltage can be decided through the Vout pin. The pair of resistors in the circuit can be connected to Vout.


To make this IC like a variable voltage regulator, a potentiometer is used to fix variable voltages at pin-1 within the potential divider. The potential difference can be formed by combining resistor R1 as well as the potentiometer at adjusting pin which controls the Vout pin accordingly. Based on the resistor value, the output voltage can be calculated using the following formula.

VOUT = 1.25 × (1 + (R2/R1)) + Iadj(R2)

Example Problem

The resistor R1 value is 240 ohms

The potentiometer R2 value is 5000

Because the value of potentiometer is 10k which is placed at 50% (50/100 of 1k is 5k).

The Iadj value is 50uA & the reference voltage is always 1.205

Vout = 1.25 * (1 + (5000/240) + (50*10-6)(5000) = 29.9V

The load regulation of LM350 provides an extremely high-quality load regulation however a few safety measures are required to attain the utmost performance. The connection of the existing set resistor can be done between the terminals like Adj and the output terminal.

LM350 Regulator using Protection Diodes

Whenever external capacitors are utilized for any regulator then sometimes it is essential to include protection diodes for avoiding the liberation of capacitors during low current point into this regulator.

Most of the 10 μF capacitors contain low sufficient internal series resistance. It delivers 20A spikes once it gets shorted. Even though the flow is short, and there is sufficient energy to harm the IC parts.

Whenever an o/p capacitor is allied to a regulator & the i/p is shorted, then the o/p capacitor will release into the regulator’s output. This mainly depends on the factors like the capacitor’s value, the regulator’s o/p voltage & the discharge rate of Vin.

The bypass capacitor can discharge over the Adj terminal during a low current junction. The discharge will occur while the input otherwise the output is shorted. The internal resistor used into the IC is a 50Ω which stops the maximum point discharge current.

Vout = 1.25(1+R2/R1) + IAdjR2


The applications of the LM350 voltage regulator include the following.

  • Positive voltage regulations
  • Current limiting circuits
  • Variable power supply
  • Reverse polarity circuits
  • The consumer products like DVD, Desktop, etc
  • In motor control circuits

Thus, this is all about the LM350 datasheet. From the above information finally, we can conclude that this is an adjustable three-terminal voltage regulator. It is used to supply in excess of 3 amperes over the output range of 1.2 volts to 33volts. It uses only two external resistors to fix the o/p voltage. Furthermore, both the regulations like line & load are similar to discrete designs. Here is a question for you, what are the main advantages of the LM350 integrated circuit?