Construction and Testing of a Step-Down DC Chopper Circuit

Experiment No:

Experiment Name:

Construction and Testing of a Step-Down DC Chopper Circuit

 Aim / Objective:

·       To construct and test a step-down (buck) DC chopper circuit.

·       To study the variation of output voltage with duty cycle.

·       To verify the operation of the buck converter in stepping down voltage.

 Theory:

A step-down DC chopper, also called a buck converter, converts a higher DC input voltage to a lower DC output voltage by rapidly switching a semiconductor device ON and OFF. The output voltage is controlled by the duty cycle $D$D of the switching signal.

·       When the switch is ON, the input voltage is applied across the load and inductor, storing energy in the inductor.

·       When the switch is OFF, the inductor releases energy to the load through the freewheeling diode, maintaining current flow.

The output voltage $V_o$ is related to input voltage $V_{in}$​ and duty cycle $D$ by the formula: Vo=D×Vin.

where $0<D<1$

 Apparatus Required:

DC Power Supply

Inductor

Capacitor

Diode

MOSFET

PWM Signal Generator

Load Resistor

Multimeter

Oscilloscope

Circuit Diagram:

Procedure:

1.      Assemble the buck converter circuit as per the circuit diagram.

2.      Set the input voltage to a constant value (e.g., 12 V).

3.      Apply a PWM signal with a low duty cycle (e.g., 20%) to the MOSFET gate.

4.      Measure and record the output voltage.

5.      Increase the duty cycle gradually (20%, 30%, ..., 80%) and record the output voltage at each step.

6.      Use an oscilloscope to observe the switching waveform and output voltage ripple.

7.      Ensure components operate within ratings.

Observation Table:

Duty Cycle (%)	Input Voltage (V)	Output Voltage (V)
20	12.0	2.4
30	12.0	3.6
40	12.0	4.8
50	12.0	6.0
60	12.0	7.2
70	12.0	8.4
80	12.0	9.6

Result:

The output voltage was successfully stepped down from the input voltage, varying proportionally with the duty cycle as predicted by $V_o=D\times V_{in}$​.

Discussion:

·       The buck converter efficiently steps down voltage with a simple switching mechanism.

·       Differences between theoretical and experimental results are due to losses in diode forward drop, inductor resistance, and switching.

·       Output voltage ripple and switching frequency impact the performance and can be optimized by component selection.

·       Buck converters are commonly used in power