LM338 Pinout, Equivalent, Features, Applications and Other Details

LM338 is a widely used 5A adjustable voltage regulator IC. In this post, we are going to discuss LM338 pinout, equivalent, features, applications and other details about how to use this IC in your design or circuits.


LM338 Pinout, Equivalent, Features, Applications and Other Details



LM338 IC Features / Technical Specifications

  • Package type TO-220
  • Capable of providing upto 5A current at the output.
  • Up to 7A output peak current
  • Voltage adjustable from 1.2V to 32V
  • less external components required
  • Only two external resistors are required for output adjustment.
  • Short circuit protection capability
  • Overheat shutdown functionality
  • Reliable to use in commercial applications
  • Maximum input voltage is 40V DC
  • Low standby current
  • Low price


LM338 Explained / Description

LM338T is a three terminal positive adjustable voltage regulator IC available in TO-220 package. The IC provides stable output voltage for example if the user set its output on 5V then it will provide stable 5V output no matter if the input voltage is fluctuating. But the user or designer of the circuit has to keep one more thing in mind that the input voltage must be 2V to 3V higher than the output voltage in any condition. To solve this problem the user should provide higher input voltage than the output for example for 5V output the input voltage can be 12V or more so if the input voltage fluctuates 3V to 5V then we still get a stable 5V at the output. One best example of this can be a solar panel that changes the output voltage frequently on a partly cloudy day.

This IC is adjustable from 1.2V to 32V DC and the maximum input voltage can be applied to the IC is 40V. LM338T can be easily used in the place of LM317 if there is a requirement for higher amperes, the IC Is capable to deliver load of upto 5A output current. However, this can also be done by using one or two high current transistors with the LM317 IC but using LM388T is still a good option if the output current requirement is under 5A.

Moreover LM338T requires very low external components because all the important circuitry is built inside the IC and hence at the output it requires only two capacitors (in some conditions), and two external resistors to adjust the output voltage. There is also an output voltage calculator available online for the IC which shows the value of the resistor to be used for a specific output.


Features Explanation

LM338 has many features which make this IC robust and reliable to use in a wide variety of educational and commercial applications. The built-in over current protection circuitry immediately shut down the IC to save it from overload damage. On the other hand, there is also a built in overheat protection circuitry which also makes shutdown the IC in case of overloads and the output NPN darlington stage get shutdown or reduces the current to save the internal circuitry from damage.


How to Use in Your Design or Circuit

The IC only required two external resistors at the output to adjust or get the desired output voltage. As shown in the circuit above one is 240 Ohms and the other is 5K variable resistor. In the place of 5K variable resistor a fixed resistor can also be used to get a fixed voltage output. Using capacitors are not necessary in case the IC is placed more than 6 inches away from the input capacitor that is used as a filter. If it is placed more than 6 inches away then an input bypass capacitor will be necessary. Another capacitor at the output can also be used to improve the output stability and transient response. When using external capacitors at the input and output of the IC, two protection diodes are must because the capacitor can deliver upto 20A spikes when they are shorted. Although the spikes are not very heavy but it contains enough power to weak or damage the internal circuitry.



Application Circuit

The applications circuit of LM338T adjustable power supply shown here is using few external components, the max input of the circuit is 40V DC and the max input amperes should be 5A to get 5A at the output. A 330nF capacitor is used at the input as a bypass capacitor and the 1uF capacitor is used to improve the output stability and transient response. Two 1N4007 diodes are used to prevent the IC from voltage spikes from capacitors. The two resistors which are 240 Ohms and 5K variable resistor are used for the output voltage adjustments. The desired output voltage from 1.2V to 25V can be set with the 5K variable resistor.

LM338 Adjustable Power Supply with Protection Diodes



Commercial power supplies

Educational power supplies

Lab power supplies

Voltage step down circuits

Battery chargers circuits

Solar power supplies

Solar battery charger circuits

Microcontroller Applications

DC to DC converters Circuits

Portable Instrument applications


Replacement and Equivalent / Other Part Numbers

LT138A, LT338A, LM138, LM2678T-ADJ, LT1084-ADJ, LT1085


How to Safely Long Run in a Circuit

To get long life performance with LM338T IC do not provide more than 40V at the input, do not drive load of more than 5A and the peak load should be more than 7A. Use protection diodes as described above, use a heat sink, and always operate the IC in temperature above 0 centigrade and below +125 degrees centigrade. The storage temperature of the IC is -65 degrees centigrade to +150 degrees centigrade.



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