DC – DC Voltage Step Down Switch Mode Buck Voltage Converter (LM2576/LM2596)

Making a highly efficient buck converter is a tough job and even seasoned engineers require multiple designs to come to the right one.

A buck converter (step-down converter) is a DC-to-DC power converter , which steps down voltage (while stepping up current) from its input (supply) to its output (load).

Switching converters (such as buck converters) provide much greater power efficiency as DC-to-DC converters than linear regulators, which are simpler circuits that lower voltages by dissipating power as heat, but do not step up output current.

The basic operation of the buck converter has the current in an inductor controlled by two switches (usually a transistor and a diode). In the idealized converter, all the components are considered to be perfect. Specifically, the switch and the diode have zero voltage drop when on and zero current flow when off, and the inductor has zero series resistance. Further, it is assumed that the input and output voltages do not change over the course of a cycle (this would imply the output capacitance as being infinite).

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Step 1: LM2576/2596, 3-A Step-Down Voltage Regulator

Features

  1. 3.3-V, 5-V, 12-V, 15-V, and Adjustable Output Versions
  2. Adjustable Version Output Voltage Range,1.23 V to 37 V (57 V for HV Version)
  3. Specified 3-A Output Current
  4. Wide Input Voltage Range: 40 V Up to 60 V for HV Version
  5. Requires Only 4 External Components
  6. 52-kHz Fixed-Frequency Internal Oscillator
  7. TTL-Shutdown Capability, Low-Power Standby Mode
  8. Monolithic integrated circuits that provide all the active functions for a step-down (buck) switching regulator
  9. High Efficiency

LM2576 DataSheet

Step 2: PCB Design

I have used EasyEda to design the 2-layer PCB.

If anyone wants i can always post the gerber files for you.

Most important design consideration to be kept in mind is that the ground terminals of the diode,caps and IC should be as close as possible.

Also the track length of Output pin of IC (pin 2) to inductor should be as short as possible.

Step 3: Ordering the PCBs

Now we have got the PCB design and it’s time to order the PCB’s. For that, you just have to go to JLCPCB.com , and click on “QUOTE NOW” button.

JLCPCB are also sponsor of this project. JLCPCB (Shenzhen JLC Electronics Co., Ltd.), is the largest PCB prototype enterprise in China and a high-tech manufacturer specializing in quick PCB prototype and small-batch PCB production. You can order a minimum of 5 PCBs for just $2. To get the PCB manufactured, upload the gerber file you downloaded in the last step. Upload the .zip file or you can also drag and drop the gerber files. After uploading the zip file, you’ll see a success message at the bottom if the file is successfully uploaded. You can review the PCB in the Gerber viewer to make sure everything is good. You can view both top and bottom of the PCB. After making sure the PCB looks good, you can now place the order at a reasonable price. You can order 5 PCBs for just $2 plus shipping. To place the order, click on “SAVE TO CART” button. My PCBs took 2 days to get manufactured and arrived within 20 days using standard registered post delivery option. There are fast delivery options also available.PCBs were well packed and the quality was really good.

Step 4: Assembling and Working

Before ordering the PCBs, always make sure that the layout and circuit is working.

I tested the circuit on perf board and then on home etched PCBs and then I ordered the PCBs.

In my circuit I have added additional points for PIN 4 and 5 to be connected to arduino or other MCU.

Pin 5 can be used as an on/off switch (active LOW), so when PIN 5 is grounded the buck converter is on and when PIN 5 is above 1.8V the converter is off.

PIN 4 is the feedback pin and with the help of PWM from arduino/MCU we can control the output voltage using an additional resistor at the resistor divider circuit.

At the end I would say that the LM2576 or LM2596 are one of the most easy buck converter IC to work with and are easily available at local electronics shop and online.

Also this IC is very forgiving and works with poor designed layouts.

I would recommend using heatsinks on IC to increase their life.

Watch the full tutorial on YT

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