• Chopper is a static device.
• It is a device which converts fixed dc input into variable
dc output voltage.
• It is also known as dc-to-dc converter.
• Widely used for motor control.
• And it is also used in switched mode power supply.
• Converter offers greater efficiency, faster response,
lower maintenance, smaller size and smooth control.
CHOPPER FED DC DRIVES
• A dc chopper is connected between a fixed-voltage dc
source and dc motor to vary the armature voltage.
• A chopper is a high speed on/off semiconductor switch
which connects source to load and disconnects the load
from source at a fast speed.
• Choppers are used to get variable dc voltage from a dc
source of fixed voltage.
• Chopper circuits are used to control both separately
excited and Series circuits.
ADVANTAGES OF CHOPPER CIRCUITS
• Ripple content in the output is small.
• Current drawn by the chopper is smaller than the
• Peak/average and rms/average current ratios are small.
• The chopper is supplied from a constant dc voltage using
• Chopper circuit is simple and can be modified to provide
regeneration and the control is also simple.
MULTIQUADRANT CHOPPER DRIVES
o Forward motoring (I-Quadrant)
o Forward Regeneration (II-Quadrant)
o Reverse motoring ( III-Quadrant)
o Reverse Regeneration (IV-Quadrant)
T1 & T4 is ON
Current Flow : VS
+ _ T1 _Motor_T4_VS
Current Ia & Va are positive
Operates in First Quadrant
T2 is OFF. Diode D2 is FB
Current flows through D3 & D2
Current Ia is negative & Va is positive.
Operates in second quadrant.
T3 & T2 is ON
Current Flow : Vdc
+ _ T3 _Motor_T2_Vdc
Current Ia & Va are negative
Operates in third Quadrant
T4 is Turned Off, D4 is FB
Current Flows through Va+ - D1 – D4 – Va-
Va is negative. But current Ia is positive
Operates in fourth quadrant
Single-Phase Half-Wave Converter Drive
(1 cos )
(1 cos )