Design of the power electronics circuitry are now-a-days reducing the size, space and weight of converter and inverter circuits. This is possible because of the availability of new high switching frequency devices. This paper presents a generalized model of buck converters that is programmable. The converter used for stepping down the voltage is called buck converter. Buck converter is designed, analysed, simulated & developed. The proposed model of this Buck converter consists of two parts: (a) Main converter circuits with the components like switch, inductor, diode, capacitor, and a load, (b) A control circuit for controlling the operation of the switch using microcontroller through digital potentiometer. This model can accurately give the power output voltage up-to three decimals.
The objective of this design is to design a programmable DC-DC buck converter for the embedded users and for industrial purpose. This is the second version of non-programmable DC-DC step down converter (Buck converter) in this board there are two inputs which is used for provide input power supply to the board one is Micro USB socket and another is two pin male header and in the output side there are three two pin headers out of which two headers having variable supply 1.23 to 11V and one is fixed 3.3V.
The variable output voltage is programmable in this version we used a atmega328p microcontroller and a 10K digital potentiometer AD5175 1024 Tap by varying the potentiometer value through program you can vary the output voltage
Atmega328p microcontroller is directly connected to a USB to serial driver IC CH340G so it is easy to program. Atmega328 microcontroller used in Arduino’s board here we can use Arduino IDE software to program this board
Use a Micro USB B 2.0 to USB Male cable to program this board.
A blue LED is connected to D13 pin same as Arduino Nano/UNO to test the board and program and another blue LED is connected to output 3.3v to test the output voltage.
Input voltage can be 5V to 24V and maximum up-to 40V.
II. BLOCK DIAGRAM
III. INDENTATIONS AND EQUATIONS
In this project I used LM2576 voltage regulator IC to get the adjustable output voltage, this is an industrial use voltage regulator IC which is widely used. The range of the output voltage vary from 1.23v to 37v with 4% tolerance. It is a monolithic integrated circuits ideally suited for easy and convenient design of a step-down switching regulator or buck converter. This ICs are available in fixed and variable output version. These regulator ICs is designed to reduce the number of components and minimize the size of buck converter and simplify the design.
IV. BASICS OF BUCK CONVERTER
The LM2576 is a “Buck” or Step−Down Converter which is the most elementary forward−mode converter. Its basic schematic can be seen in Figure 16. The operation of this regulator topology has two distinct time periods. The first one occurs when the series switch is on, the input voltage is connected to the input of the inductor. The output of the inductor is the output voltage, and the rectifier (or catch diode) is reverse biased. During this period, since there is a constant voltage source connected across the inductor, the inductor current begins to linearly ramp upwards, as described by the following equation.
During this “on” period, energy is stored within the core material in the form of magnetic flux. If the inductor is properly designed, there is sufficient energy stored to carry the requirements of the load during the “off” period
The next period is the “off” period of the power switch. When the power switch turns off, the voltage across the inductor reverses its polarity and is clamped at one diode voltage drop below ground by the catch diode. The current now flows through the catch diode thus maintaining the load current loop. This removes the stored energy from the inductor. The inductor current during this time is.
Where the R2 is Digital Potentiometer AD5175 1024 tap which is controlled by microcontroller, by varying the R2 value we can adjust the output voltage from 1.23 to 37V when R1 need to be fixed as per calculation.
Below is the circuit diagram of the final circuit.
This diagram represents the basic circuit of a voltage regulator, her HD2 connector provides the output voltage and which you can adjust through the DA1 and DW1 (Digital potentiometer) while the value of R1 will be fix.
ADC7 is used to measure the output voltage using an analog pin of microcontroller and LCD Display.
VI. DESIGNING PART
This is the final design that I had done on PCB designing tools. I used to prefer KiCAD for my work but there are many tools to design a PCB. The final design has come up with very minimum size and in good look.
Here you can see the no. of components which is SMD and THT type. It is having two input connectors and three output connectors.
VII. FINAL OUTPUT
Below is the table for parallel resistor calculator. here I set the taping value of digital potentiometer by program in microcontroller and then fixed the value of R1 10KOhm. The output value came as expected which you can see in the below table. I have tested the value from 0 to 1023 Tap but here I attached limited values. The output voltage value is correctly matching with the theoretical calculations with 5% tolerance.
After all of these my research work. I have placed the designing file for PCB manufacturing and then bought all the required components after this I assembled all the components and tested it, it is working as expected up to two decimal digit of output voltage value (my expectations was for three decimal value) but after some time I found some errors that microcontroller was not able to program perfectly may be due to some hardware issue or I used this project as a bench power supply so.
The further research is going on continuously to get the perfect efficiency up to three decimal digits of output voltage value.
 Muhammad H. Rashid, “Power Electronics: Circuits, Devices, and Application”. THIRD EDITION.
 R. D. Middlebrook, “Power Electronics: Topologies, Modeling and Measurement”. Proc. IEEE Int. Symp. Circuits System, April 1981.
 Robert W. Erickson and Dragon Maksimoni, “Fundamentals of Power Electronics”. SECOND EDITION, Springer International Edition.
 Wikipedia, the Free Encyclopedia, “Buck Converter (online), Available from http://en.wikipedia.org/wiki/Buck converter”.
 Wikipedia, the Free Encyclopedia, “Boost Converter (online), Available from http://en.wikipedia.org/wiki/Boost converter”.
 Wikipedia, the Free Encyclopedia, “Buck-boost Converter (online), Available from http://en.wikipedia.org/wiki/Buck-boost converter”.