# Buck converter simulation using PSpice : tutorial 8

In this tutorial I will explain you the working of a buck converter which is used to convert the voltage or current of the source to a desired level. The converter is then explained and simulated using PSPICE. At the start a brief and concise introduction of converters specifically buck converts along with their circuit diagram is provided with the explanation of the output they will show. After that the circuits is simulated using PSPICE and the result are compared with the theoretical discussion provided (which should be same). At the end of the tutorial you are provided with an exercise to do it by yourself, and in the next tutorials I will assume that you have done those exercises and I will not explain the concept regarding them

### Introduction to Buck Converter simulation in PSpice

A buck converter is the one which converts the DC voltage level of an input source to a lower value and shift the current level of the source to a higher value at the output. A simple circuit diagram of a buck converter is shown in the figure below,

Figure 1: Buck converter

The switch in the circuit is the main component and it controls the voltage level at the output, and the on and off states of the switch are shown in the figure below,

Figure 2: On off states

### How to design Buck converter in PSPICE

• Lets’ design a simple circuit of a buck converter which is to be discussed in this tutorial and the boost converter with a few details provided is left for you as an exercise. Open the PSPICE design manager on your PC by typing design manager in the search bar. From the design manager click on the run schematic button to open a new blank schematic as shown in the figure below,

Figure 3: Opening schematic

• After opening the new schematic before jumping into designing first save the schematic by clicking on the file button at the top left corner and then selecting save as so that we can access it anytime in the future. Refer to the figure below,

Figure 4: Saving schematic

• Click on the get new part icon at the top bar of the schematic window in order to search for the components that are needed for circuit designing.

Figure 5: getting new part

• In the get new part window, type ‘d’ it will display all the diodes available in PSPICE. From that list select a simple diode as shown in the figure below,

Figure 6: Placing diode

• Again open the get new part window and in the part name block type ‘L’, select the inductor from the list given and then click on place & close as shown in the figure below

Figure 7: Placing inductor

• Again open the get new part window and in the part name block type C, select the capacitor from the list given and then click on place & close as shown in the figure below

Figure 8: Placing capacitor

• Again open the get new part window and in the part name block type ‘R’, select the resistor from the list given and then click on place & close as shown in the figure below

Figure 9: Placing resistor

• This resistor will act as a load in the circuit. Again open the get new part window and in the part name block type Vdc, select the supply from the list given and then click on place & close as shown in the figure below

Figure 10: Placing DC supply

• Now we have to place a switch which is the main component in the buck converter circuit diagram, open the get part window and type “S” in it and select the switch that pop up first as shown in the figure below,

Figure 11: Placing switch

• Also we have to supply a pulsating dc or you can say a pwm waveform using a pulse source. In the get part window type VPULSE and place the component as shown in the figure below,

Figure 12: Placing VPULSE

• Next step is to place a ground, do the same again and in the part name type Gnd and select the ground and then click on place & close as shown in the figure below,

Figure 13: Placing ground

• The placed components in the schematic window are shown in the figure below,

Figure 14: Placed components

• Click on the draw wire icon at the top bar of the schematic window in order to connect the already placed components for circuit designing.

Figure 15: Drawing wire

• Connect all the components to complete the circuit diagram as shown in the figure below,

Figure 16: Complete circuit diagram

• On the top of the schematic window, click on the Voltage/Level Marker button as shown in the figure below,

Figure 17: Voltage marker

• Place it at the output resistor and at the input node as shown in the figure below,

Figure 18: Placed voltage marker

• Next step is to set the attributes of the input VPULSE voltage supply connected to operate the switch. Double click on the input supply you connected in the circuit previously and set the magnitude of the all the attributes as shown in the figure below,

Figure 19: VPULSE attributes

• Adjust the value of the input dc source to 10 volts as shown in the figure below,

Figure 20: Input voltage

• Set the value of the capacitor to 100u as shown in the figure below,

Figure 21: Capacitor value

• Set the value of the load resistor to 10 ohms as it will make the voltage difference obvious as shown in the figure below,

Figure 22: Resistor value

• Next step is to adjust the properties of the simulations in order to produce the graph of the voltage at the marker. Click on analysis and then click on Setup as shown in the figure below

Figure 2123: Analysis setup

• A widow will appear, click on the transient block on the window and adjust the properties of the window according to your requirement, refer to the figure below

Figure 2224: Transient properties

• Now comes the simulation part, click on the analysis at the top bar of the schematic window and then click on simulate as shown in the figure below,

Figure 23: Simulating

• A schematic window will appear showing the voltage across the load resistor as shown in the figure below,

Figure 25: Output and input voltage

• The red waveform is the voltage level across the output whereas the green waveform implies the input voltage level. As we have discussed in the introduction part the voltage level of output should be lower than the input thus the simulation gives the same results. Converting the voltage markers to current markers and the current at the output will be higher as shown in the figure below,

Figure 26: Output current

The boost converter is another type of a DC level converter which is opposite to that of the buck converter i.e. it increases the voltage level at the output compared to the input and decreases the current level at the output compared to the input current level.

Exercise:

• Design and simulate a boost converter using PSPICE.

(Hint: The voltage level at the output will be higher than the input voltage as the name suggests)

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