LM2678 5 Amp Step-down Voltage Regulator

Last Updated on March 16, 2024

Simple Step down Voltage Regulator Circuit designed by using IC LM2678 from Texas Instruments. This circuit takes 8V to 40 Volts as input and gives 5V/5 Amps (5 Volt, 5A) regulated DC as output. This LM2678 series of regulator are monolithic integrated circuit which provide all of the active functions for step down(buck) switching regulator.

IC LM2678 is capable of driving up to 5A load with regulation characteristics. The series consists of fixed output voltages of 3.3V,5V, and 12V an adjustable output version. As stated in the datasheet “The LM2678 series also has built-in thermal shutdown, current limiting, and an ON/OFF control input that can power down the regulator to a low 50μA quiescent current standby condition. The output voltage is ensured to a ±2% tolerance. The clock frequency is controlled to within a ±11% tolerance.” Refer LM2678 Datasheet for more Information.

Circuit Diagram


S NoDesignatorValueQuantity
1Transformer T18V to 40V1
6U1 ICLM 26781

Construction and working

In this step down voltage regulator circuit we have taken has an internal 5 Volt Regulator , 260KHz oscillator, and it also contain the blocks foe thermal shut down. Here T1 Transformer can be a 230V primary , 25V secondary, 5A step down transformer. Now rectified DC supply from bridge rectifier with 8V to 40Volt applied to the Vin pin through filter capacitor. Pin 4 is for the ground.

The capacitor are used for filtering purposes. Pin 3 is for the bootstrap capacitor connection .After these connection switch output is applied to the inductor and capacitor at the end we get the 5V voltage with 5A of current at the output. Connect any load of this voltage. IC LM2678 need only few components for its full operation. This IC consumes 50μA stand by current when switch off condition and this is very low when compared to its peers. LM2678 Contains DMOS Power MOSFET hence it can handle high current power supply designs with low external components.

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