This document summarizes a seminar presentation on DC-DC converters. It discusses how DC-DC converters, also known as choppers, are increasingly important for applications that require variable DC voltage levels, such as subway cars and electric vehicles. Choppers use fast switching devices like transistors to rapidly connect and disconnect a load from the power source, producing a chopped or variable output voltage. The document focuses on step-down choppers, which reduce the input voltage level, and describes how the duty cycle of the switching device controls the output voltage. Resistive load examples are provided to illustrate how step-down choppers work.

1. A
seminar
on
DC-DC Converter
PRESENTED BY :
Sanjay Kumar 8th SEM / 4rd YEAR
ELECTRICAL DEPARMENT MITS
JADAN,PALI
GUIDE BY :
Mr. HITESH JAIN (Asst. Professor)
ELECTRICAL DEPARMENT
MITS JADAN,PALI

2.  DC to DC converter is very much needed nowadays as many industrial
applications are dependent upon DC voltage source. The performance of these
applications will be improved if we use a variable DC supply. It will help to
improve controllability of the equipments also. Examples of such applications are
subway cars, trolley buses, battery operated vehicles etc. We can control and
vary a constant dc voltage with the help of a chopper.
 Chopper is a basically static power electronics device which converts fixed dc
voltage / power to variable dc voltage or power. It is nothing but a high speed
switch which connects and disconnects the load from source at a high rate to get
variable or chopped voltage at the output.

3.  Chopper can increase or decrease the dc voltage level at its opposite side. So,
chopper serves the same purpose in dc circuit transfers in case of ac circuit. So it
is also known as DC transformer.
 Devices used in Chopper
 Low power application : GTO, IGBT, Power BJT, Power MOSFET etc. High power
application : Thyristor or SCR.
 These devices are represented as a switch in a dotted box for simplicity. When it
is closed current can flow in the direction of arrow only.

4.  ) Step down Chopper : Step down chopper as Buck converted is used to reduce
the i/p voltage level at the output side. Circuit diagram of a step down chopper
is shown in the adjacent figure.

5.  When CH is turned ON, Vs directly appears across the load as shown in figure. So
VO = VS.

6.  When CH is turned off, Vs is disconnected from the load. So output voltage VO = 0.

7.  The voltage waveform of step down chopper is shown below:

8.  TON → It is the interval in which chopper is in ON state. TOFF → It is the interval in
which chopper is in OFF state. VS → Source or input voltage. VO → Output or load
voltage. T → Chopping period = TON + TOFF
 Operation of Step Down Chopper with Resistive Load
 When CH is ON, VO = VS When CH is OFF, VO = 0

9. Where, D is duty cycle = TON/T. TON can be varied from 0 to T, so 0 ≤ D ≤ 1. Hence
output voltage VO can be varied from 0 to VS.

10.  So, we can conclude that output voltage is always less than the input voltage
and hence the name step down chopper is justified. The output voltage and
current waveform of step down chopper with resistive load is shown below.

11. THANK
YOU