Circuit Diagram of 5V Buck Regulator using LM2678

There are many manufacturers of buck regulators with both synchronous and asynchronous switches. These regulators offer typical features like input voltage capacity, switching frequencies, and high-efficiency operation. With burst mode operation, inactive currents in the tens of micro-amps level can be achieved. This mixture of features permits extremely small, low outline buck switching regulator circuit implementations with external components. This article gives an overview of 5V buck regulator using LM2678.

What is a Buck Regulator?

The buck regulator is a very simple kind of DC-DC converter that gives an output voltage which is less than its input. This converter is so called because the inductor always “bucks” or performs next to the input voltage. The output voltage of a supreme buck converter is equivalent to the product of the switching duty cycle and also the supply voltage.

Buck Converter
Buck Converter

5V Buck Regulator using LM2678

The LM2678 IC is monolithic integrated circuits (IC) for a step-down switching voltage regulator accomplished by driving up to 5A loads with characteristics like outstanding line and load regulation. The efficiency of this IC is high (>90%), which is gained through the use of a low ON-resistance DMOS power switch. The sequence includes permanent output voltages of 3.3V, 5V and 12V and a modifiable output version.

LM2678 IC
LM2678 IC

Features of LM2678

The features of LM2678 include the following.

  • It has up to 92% of Efficiency
  • Simple to design with (using off-the-shelf external components)
  • DMOS output switch will be 120 mΩ
  • Fixed outputs like 3.3V, 5V and 12V and changeable versions (1.2V to 37V )
  • When it switched OFF then the standby current will be 50μA
    Maximum o/p tolerance is ±2% over full line and load conditions
  • Wide i/p voltage range ranges from 8V to 40V
  • 260 KHz fixed frequency internal oscillator

The Applications of LM2678 include the following

  • Designing of LM2678 IC is very simple, efficiency is high (>90%) step-down switching voltage regulators
  • Efficient system pre-regulator for linear voltage regulators
  • Used in Battery chargers

5V Buck Regulator using LM2678 Circuit

The circuit diagram of a 5V buck regulator based on the LM2678IC is shown below. IC LM2678 regulator is monolithic integrated circuits which supply all required functions for a buck switching regulator and it can drive up to 5A loads.

5V Buck Regulator Circuit
5V Buck Regulator Circuit

The IC LM2678 has more than 90% efficiency and also line regulation and outstanding load. This is accessible in three-set output voltages such as 3.3V, 5V, 12V and a modifiable output version. The IC is also having some features like current limiting, thermal shutdown, and ON/OFF control.

The circuit gives an output of 5V because it is based on LM2678-5.0 version. The regulator input voltage is fed to the pin-2 of the integrated circuit. Here input bypass capacitors are C1 to C4. They also supply current to the control switch of ICs when it is activated first. Capacitor C5 enhances the gate drive of the inside MOSFET and makes it fully ON.

This reduces switching drops and helps to reach high efficiency. If the pin-7 (ON/OFF pin) is connected to the ground terminal then the pin will shut down. Present drain throughout the shutdown mode will be less than <50uA. Schottky diode (D1) is used as a freewheeling diode. When the control switch or internal MOSFET is turned OFF, then the current from L1 inductor flows through this diode. Capacitors C6 & C7 and output filter capacitors.

This article has given a brief introduction to buck regulator, which is used in various cool applications like smartphones, tablets, laptops, portable battery packs, quadcopters, flashlights. Audio amplifiers and motor control circuits have a huge deal in frequent with buck converters. We hope that you have got a better understanding of this concept. Furthermore, any doubts regarding this concept or to implement any electrical projects please give your valuable suggestions by commenting in the comment section below. Here is a question for you, what is the function of a regulator?

2 Comments

  1. mnr electrical says:

    gives a clear idea. very useful article. Thanks for sharing

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