PB Fortich

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  • 5V Power Supply using Buck Converter

  • Created: Mar 02, 2016

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The reference design is a simple 5V switching power supply that uses a Buck converter. It features Texas Instrument’s LM2678, a high efficiency, 5A step-down voltage regulator. Its efficiency is up to 92% since it’s a switching regulator. It can have a fixed output voltage of 3.3V, 5V, and 12V, and an adjustable voltage from 1.2V to 37V. Also, it can accept a wide range input voltage. The input voltage can range from 8V to 40V.

The design shown is a typical setup for the device. Each component is selected for a specific application, this time, a 5V, 2A power supply. The source for the design is a 220V AC, 60Hz supply which then gives a 12V RMS after it is being stepped down by the transformer. The source is the rectified so that it will give a somewhat DC supply with a frequency of 120Hz. After rectification, the signal is filtered using a “smoothing” capacitor. This will form the signal into a much better shape with fewer ripples. The signal is then fed to the LM2678 buck converter which efficiently gives a 5V regulated voltage with a current of 2A. The device does a switching action that will turn on and off the supply voltage with the use of PWM. This in turn will give out the average voltage on the output. The duty cycle of the PWM is a crucial factor in this operation. It is the one that determines the output DC voltage. The inductor in the circuit prevents any sudden change in the current thus, maintaining the 2A output current. While the two capacitors, C3 and C4, prevent any sudden change in the voltage thus, smoothens out the output DC voltage. The Schottky diode found in the circuit protects the device from inductive spiking which could be very harmful to the circuit. It blocks the large negative voltage that is produced by the inductor when the circuit is pulled out of supply.

Typical applications for this design is cellphone charging, microcontroller voltage supply, DC motors, or any electronics project that require 5V input voltage.



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