Switch-Mode Power Supply Circuit using LM2674

Overview

For years, National Semiconductor has crafted and designed integrated circuits (ICs) tailored for switch-mode power supplies. Utilizing these devices is typically straightforward, thanks to the detailed documentation at hand. Take, for instance, the LM2671 or LM2674-based switch-mode power supply, a common example. These supplies come in variants capable of delivering outputs at 3.3 V, 5 V, and 12 V, with a version even offering presettable output voltage. In their designated application, these supplies can handle currents up to 500 mA. Notably, they operate at a high switching frequency of 260 kHz.

In today’s tutorial, we are going to make a “Switch-Mode Power Supply Circuit” using an lm2674.

Hardware Components

You’ll need the following hardware components to get started:

S.no	Components	Value	Qty
1	Integrated Circuit IC	LM2674	1
2	Diodes	–	1
3	Capacitors	C1 = 100µ 40V C2 = 10nF C3 = 100µ 10V	1 1 1
4	Inductors	150uH

Schematic

The benefit here lies in the requirement for only low-value inductors and capacitors, resulting in exceptional efficiency and compact dimensions. Typically, efficiency stands at 90% under normal conditions and can even reach up to 96%. Both ICs come with safeguards against current and temperature overloads. The LM2671 boasts additional features like a soft start and the ability to sync with an external clock, facilitating the synchronized operation of multiple supplies for enhanced EMC control. In the diagram’s depicted application, a 5 V output voltage and up to 500 mA output current are achieved. Diode D1, being of the Schottky type (with Uco≥ 45 V and Imax≥ 3 A), is included in the setup. National Semiconductor has a long history of manufacturing and designing ICs specifically tailored for switch-mode power supplies.

The straightforward nature of these devices’ applications is aided by the comprehensive documentation available. An illustrative example of such a power supply is one based on the LM2671 or LM2674, with component options for outputs at 3.3 V, 5 V, and 12 V, including a version with presettable output voltage. These supplies can deliver currents of up to 500 mA within their designated application, notable for their high switching frequency of 260 kHz.

The benefit of this setup is that it requires only low-value inductors and capacitors, leading to excellent efficiency and a compact design. Under normal conditions, efficiency reaches 90% and can even peak at 96%. Both ICs come equipped with safeguards against current and temperature overloads. The LM2671 offers additional features like a soft start and the ability to synchronize with an external clock. This synchronization option allows multiple supplies to sync up, providing better control over ElectroMagnetic Compatibility (EMC) issues. In the diagram’s configuration, an output voltage of 5 V and a maximum output current of 500 mA is achieved. The diode D1 used is of the Schottky type, with a minimum reverse breakdown voltage (Uco) of 45 V and a maximum forward current (Imax) of 3 A