A voltage regulator is an electronic device used to maintain a power source’s voltage at suitable limits. This device is mainly required to maintain voltages in the set range that can be accepted by the equipment through that voltage. Such type of device is used extensively in all kinds of motor vehicles to match the generator’s o/p voltage to the electrical load as well as to the charging necessities of the battery. Voltage regulators are utilized within electronic equipment where extreme changes in voltage would be harmful. There are two kinds of voltage regulators: linear & switching. These regulators are used to control the voltage of a system, although linear regulator operates with low efficiency whereas switching regulator operates with high efficiency. This article provides brief information on the LM338 voltage regulator, pin configuration, specifications, circuit, working, and its applications.
What is the LM338 Voltage Regulator?
The LM338 voltage regulator is a versatile integrated circuit that can be connected in different ways to get high-quality power supply circuit arrangements. This is a three-terminal adjustable positive voltage regulator and is capable of supplying more than 5A above a 1.2V to 32V o/p range. This IC is very simple to use & needs two resistors only to set the o/p voltage. The LM338 family has a unique time-dependent current limiting feature.
The LM338 voltage regulator IC can be adjustable from 1.2Volts to 32V DC. The highest input voltage that can be provided to this regulator IC is approximately 40V. This IC can be used easily instead of LM317 if there is a necessity for high amperes. This IC is still a better option to choose if the requirement of output current is below 5A. In addition, this IC needs very less external components because all the significant circuitry is built within the chip and therefore it needs two capacitors only at the output & two exterior resistors to regulate the o/p voltage.
The LM338 voltage regulator pin configuration is shown below. This IC includes three pins which are discussed below.
- Pin1 (IN): This is an input pin that is connected directly to the i/p voltage source.
- Pin2 (Out): This is an output pin that is used to provide the regulated o/p voltage.
- Pin3 (Adj): This is an adjust pin, used to adjust the o/p voltage based on the desired level.
Features & Specifications:
The features and specifications of the LM338 voltage regulator include the following.
- It is available in a TO-220-type package.
- It has guaranteed thermal regulation.
- It has guaranteed 5A of o/p current.
- It has guaranteed 7A of peak o/p current.
- It has adjustable o/p down to 1.2Volts.
- Its o/p is protected from short-circuit.
- It provides upto 5A of current at the o/p.
- It has adjustable voltage from 1.2Volts to 32Volts.
- It needs fewer external components.
- It needs two external resistors for adjustment of output.
- It has the functionality of overheating shutdown.
- It is consistent to utilize within commercial applications
- Its maximum i/p voltage is around 40V DC.
- Its dropout voltage typically is 1.5V.
- Its ripple rejection typically is 80dB.
- It has a low standby current.
- These are available in low prices.
- This IC is reliable and robust.
- It has built-in overcurrent protection.
- Equivalent & Replacement of LM338 voltage regulators are; LT338A, LT138A, LM138, LT1084-ADJ, LM2678T-ADJ, LT1085
How to Securely Use LM338 Voltage Regulator in a Circuit?
To use the LM338 voltage regulator within a circuit for a long time, this IC should not provide above 40V at the i/p. This IC does not drive any load above 5A & the peak load must be above 7A. Protection diodes and a heat sink must be used. This IC must be operated in temperatures> 0 degrees C < +125 degrees C. The storage temperature of this IC must be > -65 degrees C < +150 degrees C.
Adjustable Voltage Regulator Circuit with LM338 IC
Generally in different electrical and electronic circuits, there is no voltage controllers are used, thus if there is any adjustment within the input voltage, then it would appear at the output. So such kinds of circuits are used mostly for DC motors, LED lights, and many more. So, we know that unregulated voltage permits change at the output side.
However, these changes for TVs or laptops can be hazardous because they can cause poor regulation, temperature variation, etc. To overcome this, voltage regulators are used so that they decrease the fluctuations and ripples within the voltages. So an adjustable voltage regulator circuit with LM338 IC is designed which is shown below.
The required components to make this simple adjustable voltage regulator circuit mainly include; LM338 IC, 2-Pin connector, 1N5821 diode, 7LTX17.5µH Inductor, 10µF/25V, and 4.7µF/25V 5 electrolyte capacitor, 120Ω resistor, 1N4007 diode, and 1K variable resistor. Connect the circuit as per the diagram shown below.
This circuit is designed with LM338 voltage regulator IC which has three terminals. At pin 3 of this IC, unregulated supply can be supplied. The potentiometer is connected at pin 1 of the IC. So the output voltage can be decided by the potentiometer and R1 resistor together. The regulated voltage at the output can be changed by changing the potentiometer. In the circuit, the two diodes are used as reverse protection components to absorb the spikes & defend the entire circuit. Adjustable voltages can be monitored at the o/p C2 capacitor. These circuits are used in laptops, power supply circuits, and many more electronic devices.
While designing any circuit using an LM338 voltage regulator, some particular considerations can improve performance which are discussed below.
Dissipation of Heat
The LM338 voltage regulator produces heat while operating at higher currents. So sufficient heat sinking measures should be implemented to stop overheating & ensure correct functioning like; providing adequate airflow or using a heat sink.
Protecting the LM338 voltage regulator from extreme current is essential. So a current-limiting resistor must be added in series through the ADJ pin to avoid harm caused by sudden high currents.
Input & Output Capacitors
In the circuit, input & output capacitors are recommended to use to maintain stability as well as decrease noise. These capacitors assist in filtering out unnecessary signals & providing a consistent & smooth voltage supply.
Voltage Surge Protection
When the input voltage in the circuit faces sudden surges or spikes then this voltage regulator may be vulnerable to harm. So protective measures need to be incorporated like; transient voltage suppressors to protect this regulator from voltage transients.
LM338 IC is a reliable voltage regulator so while designing any circuit, some issues may occur. Here some common troubleshooting tips are discussed below. Some precautions need to be taken before connecting a voltage regulator to a circuit. To know how, please refer to this link: Precaution to be taken while connecting a constant current voltage regulator to a circuit.
Instability of Voltage
If the regulated o/p voltage is not stable, then make sure the input & output capacitors for correctly installed and also check whether they are in the suggested capacitance values or not.
If the LM338 voltage regulator is overheated, then make sure that it is heat-sinked correctly or not. Confirm the differentials of input & output voltage and check whether they are within the specified limits of the regulator or not.
If the o/p voltage shows a major ripple, validate the quality of input & output capacitors and make sure that they are connected properly or not.
No O/P Voltage
If the voltage regulator IC does not provide any o/p voltage, then check the connections of the circuit and verify any short/open circuits. Make sure that the i/p voltage is in the particular operating range or not.
LM338 Voltage Regulator Applications
The applications of the LM338 voltage regulator are discussed below.
- LM338 voltage regulators are used in power supply units, battery chargers, audio amplifiers, LED lighting systems, and testing & measurement equipment.
- These ICs are used in various electronic projects because they are versatile.
- These are used in lab, educational, solar, and commercial power supplies.
- These voltage regulator ICs are used in different circuits like; voltage step-down, DC to DC converter, solar battery charger, microcontroller, and portable instrument-based applications.
Please refer to this link for the LM338 voltage regulator datasheet.
Thus, this is an overview of the LM338 voltage regulator. Generally, voltage regulation is the procedure used to maintain a stable o/p voltage in spite of changes within the load conditions or input voltage. It is necessary to ensure reliable electronic devices or systems operation. So LM338 voltage regulator is used by engineers to attain accurate control above the preferred levels of voltage by enabling the best performance & safety of electronic components. Here is a question for you, what is an LM340 voltage regulator?