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Step Up/ Step Down Chopper
his is also known as a buck-boost converter. It makes it possible to increase or reduce the voltage input
level. The diagram below shows a buck-boost chopper
Figure: 3.9 circuit diagram of step up chopper
When the chopper is
switched ON, the inductor L becomes charged by the source voltage V
s
. Therefore,
V
s
= V
L
.
,
When the chopper is switched OFF, the inductor’s polarity reverses and
this causes it to discharge
through the diode and the load.
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Hence,
V0 = −VL
By comparing the above equations
V
0
=
Principle of operation of class A chopper
Class A Chopper is a first quadrant chopper
• When
chopper is ON, supply voltage V is connected across the load.
• When chopper is OFF, vO = 0 and the load current continues to flow in the same
direction through the
FWD.
• The average values of output voltage and current are always positive. Class A Choppe
r is a first
quadrant chopper
• When chopper is ON, supply voltage V is connected across the load.
• When chopper is OFF, vO = 0 and the load current continues to flow in the same direction through the
FWD.
• The average values of output voltage and
current are always positive.
•
Class A Chopper is a step
-down chopper in which power always flows form source to load.
• It is used to control the speed of dc motor.
• The output current equations obtained in step down chopper with R
-L load can be used to study the
performance of Class A Chopper.