This document provides an introduction to DC-DC converters known as choppers. It discusses the principle of operation where a chopper uses a switching device to vary the duty cycle and produce a chopped DC voltage at the load. This allows obtaining a variable DC output voltage from a constant DC source. Specific converter circuits are described including buck converters for stepping down voltage, boost converters for stepping up voltage, and buck-boost converters for both stepping up or down voltage. The operation and analysis of these converters is explained through diagrams and waveforms.

1. Introduction to DC-DC Converter
ChopperFixed DC Supply
Variable DC Output

2. Contents
 What is chopper
 Principle of operation of chopper
 Steady state analysis
 Switch mode regulator..
.Buck converter (Step-down converter)
.Boost converter (Step-up converter)
.Buck-Boost converter (Step-down/step-up converter) and

3.  A chopper is a static device which is used to obtain a variable dc
voltage from a constant dc voltage source.
 Also known as dc‐to‐dc converter.
 It offers greater efficiency, faster response, lower maintenance,
smaller size and smooth control.
 Widely used in trolley cars, battery operated vehicles, traction
motor control, control of large number of dc motors, etc…
 …..

4.  Principle of Chopper Operation
Output wave form
Chopper circuit
Toff

5. • During the time period Ton the chopper is turned on and the
load voltage is equal to source voltage Vs.
• During the interval Toff the chopper is off and the load current will
be flowing though the freewheeling diode FD .
The load terminals are short circuited by FD and the load voltage is
therefore zero during Toff. Thus, a chopped dc voltage is produced
at the load terminals.
We can see from the graph that the load current is continuous.
During the time period Ton, load current rises but during Toff load
current decays .

6. Average load Voltage,
V0 = Ton/ (Ton +Toff) * Vs = (Ton/T) V
’
here T = Ton +Toff
A = Ton /T = duty cycle
So ‘ V0=A Vs
& V0 = f. Ton .Vs
f= 1/T = chopping frequency

7. Output
voltage
Output
current
v0
V
i0
Imax
Imin
t
t
tON
T
tOFF
Continuous
current
Output
current
t
Discontinuous
current
i0

8. V
i0
V0
R
L
E
+
-

11. Step-Down Step-Up Step-Down/Up

12. As shown in Fig. the buck converter consists of a DC supply or a
rectified AC output, two switches i.e. D (diode) and S (can be
semi-controlled or fully-controlled power electronics switches),
two-pole low-pass filter (L and C) and a load.
(i) When the switch is ON condition (ie, TON), the input provides
energy to inductor and output.
(ii) The difference between the input and output voltage is applied
to inductor as shown in waveform.
(iii) When the switch is turned off, the inductor current will flow in
the same direction to load. It is inductor property to maintain the
current flow in the same direction.
(iv) The freewheeling diode D1 is forward biased at this time and
completes the inductor current path.
Let the duty ratio of switch S be…
D =Ton/T whrer T= Ton+ Toff

13. The first mode is when the switch S is on

14. Mode 2:

15. Waveform..
Here : D is the duty cycle.
It represents the fraction
of the commutation period
T during which the switch
is On.

17. When S is turned on..

19. Waveform..