Power Electronic subject

1. LAB.NO.12: To Design Buck Converter.
Subject: Power Electronics ET-317(L)
 SUBMITTED BY
 Name: KIFAYAT ULLAH
 ID: 11241
 Program: BSC. EET
 Semester: 4th
Submitted to (Teacher Name): Sir Abdullah
SIGNATURE:
City University of Science andInformation TechnologyPeshawar

2. Experiment NO.12
Title:
To Design Buck Converter.
Objective:
In this lab we will study and know about to design buck converter.
Apparatus:
 DC power supply
 MOSFET Switch (IRF1010NS)
 Signal voltage source (Clock Voltage)
 One Power diode (IN4001)
 Inductor
 Capacitor
 Load Resister
 Connecting wires
 Power electronics trainer
 Oscilloscope
Modern Tool:
Multisim
Theory:
Buck converter is a DC-DC converter which will step down a higher voltage to a
lower voltage level, that means output voltage magnitude is less than the input voltage magnitude.
It uses a power semiconductor device as a switch to turn on and off the DC supply to the load. The
switching action can be implemented by a BJT, a MOSFET, or an IGBT. Figure 1 shows a
simplified block diagram of a buck converter that accepts a DC input and uses pulse-width
modulation (PWM) of switching frequency to control the switch. An external diode, together with
external inductor and output capacitor, produces the regulated dc output. Buck, or step-down
converters produce an average output voltage lower than the input source voltage.

3. The following diagram shows the working operation of the buck converter. In the buck converter
first transistor is turned ON and second transistor is switched OFF due to high square wave
frequency. If the gate terminal of the first transistor is more than the current pass through the
magnetic field, charging C, and it supplies the load. The D1 is the Schottky diode and it is turned
OFF due to the positive voltage to the cathode.
The inductor L is the initial source of current. If the first transistor is OFF by using the control
unit, then the current flow in the buck operation. The magnetic field of the inductor is collapsed
and the back e.m.f is generated collapsing field turn around the polarity of the voltage across the
inductor. The current flows in the diode D2, the load and the D1 diode will be turned ON.
The discharge of the inductor L decreases with the help of the current. During the first transistor
is in one state the charge of the accumulator in the capacitor. The current flows through the load
and during the off period keeping Vout reasonably. Hence it keeps the minimum ripple amplitude
and Vout closes to the value of Vs
Circuit Diagram:
Procedure:
 First of all, we took all the apparatus and keep on the experiment table.
 Then we connect all the connection as shown in circuit diagram on the power electronic trainer.
 Then we adjust the MOSFET switch and given their values of the duty cycle is 50, frequency
is 1kHz, signal volage is 10v.

4.  Then we give the DC power supply which is V1(12v).
 After suppling the DC voltage, we saw the values of parameters.
 Which was the Buck converter.
 Then we noted the values of buck converter.
 Then we repeat the experiment.
Observation Table:
S. No 𝑽𝟏 (V) D.C 𝑽𝒐 (V) 𝑰𝒊 (A) 𝑰𝟎 (A) 𝑷𝒊 (W) 𝑷𝒐(𝑾) Gain =
𝒐/𝒑
𝒊/𝒑
01 12 70% 8.09 1.16 1.62 14 13
02 12 50% 5.53 0.578 1.11 7 6
03 12 30% 3.25 0.217 0.651 2.60 2.11
Calculation:
Input Power.
𝑷𝒊 = 𝑽𝟏𝑰𝒊 = 12V*1.16A = 14W
Output Power.
𝑷𝒐 = 𝑽𝒐𝑰𝒐 = 8.09V*1.62A = 13W
Gain.
Gain =
𝒐/𝒑
𝒊/𝒑
=
Conclusion:
In this lab we studied and learn about buck converter and its connection and their working operation of
the Buck Converter.