Buck Convertor simulation in LTSPICE

 I have been doing a buck converter simulation recently.

Let's go with some basic or normally used requirements for the buck converter.


1. The first step would be calculating ripple current.

`\triangle I= K\times I_{out}`

`\triangle I= 1  Amps`

2. Now, calculate the ripple Voltage

`\triangle V= V_{r}\times V_{out}`

                                                `\triangle V= 5mV`

3. Let's calculate the Duty cycle, D

`D=\frac{V_{out}}{V_{i n}}`

`D=0.4167`

4. The value of the Inductor can be calculated by

`  L=\frac{Vi n\times D\times (1-D)}{\triangle I \times F_{s}}`

`L=116 mH`

5. Finally, calculating the output Capacitance value

`C=\frac{Vi n\times D\times (1-D)}{8\times\triangle V\times L\times C \times F_{s}^{2}}`

`C=1mF`

I made an Excel with the formula. I have given the snapshot of answers for the above requirement

Below is the Excel sheet for reference.
https://docs.google.com/spreadsheets/d/1g6hk6d9Injx8KBXFID2UZ6RKuIQoyRD5ycpD0WzAQt8/edit?usp=sharing

LTSPICE Simulation:

Now, it's time for the LTspice simulation.

So I defined the duty cycle and switching frequency as parameters and used the PWM signal for turning on and off the MOSFET. I have given the load resistance as 1 ohm.
Running the simulation gives the following results.

Output Voltage:


The output voltage comes under 4.45V, not the actual 5V. Since I am using very little load and drawing more current, there is a voltage dip at the output.

Load Current:

The Load current comes around 4.45A. Its follows basic ohms law. 4.45V divided by 1 ohm equals to 4..45A.

Inductor Current:


As calculated, the Inductor ripple current comes to around 1A.

Output ripple voltage:


As calculated, the output ripple voltage comes to around 5mV.

Interesting thing here is that we know the Load current, `I_{Out}= I_{L}-I_{C}`

From the above image, we can clearly see that most of the inductor ripple current flows through the capacitor, and we will get the DC current at the output.












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