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DC-DC Converters (Choppers)

DC-DC converters can step up or step down DC voltages using switching circuits. A buck converter steps down voltage using a transistor switch and diode. The duty cycle of the switch controls the output voltage. A boost converter steps up voltage using a switch, diode, and capacitor. During the on cycle, current flows through an inductor, and during the off cycle the inductor voltage adds to the input voltage. DC-DC converters are classified based on the quadrants of input and output voltage/current they can operate in, from first quadrant only to all four quadrants.

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65 views14 pages

DC-DC Converters (Choppers)

DC-DC converters can step up or step down DC voltages using switching circuits. A buck converter steps down voltage using a transistor switch and diode. The duty cycle of the switch controls the output voltage. A boost converter steps up voltage using a switch, diode, and capacitor. During the on cycle, current flows through an inductor, and during the off cycle the inductor voltage adds to the input voltage. DC-DC converters are classified based on the quadrants of input and output voltage/current they can operate in, from first quadrant only to all four quadrants.

Uploaded by

Bharat
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PPT, PDF, TXT or read online on Scribd
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DC-DC Converters (choppers)

The objective is to convert a fixed DC voltage to a


variable DC voltage

It is possible to step up and step down voltage.

Voltage step down (buck converter)


First, suppose L=0, E=0.
The diode is not needed.
Va=(ton/T)Vs
k=ton/T is the duty cycle
VRMS=k1/2Vs

2
Pout=(kVs )/R

Step down converter with


RL load

Pspice schematics Step down dc-dc converter

Voltage step up (boost)


converter
On mode:

VL=L(di/dt)

Off mode: Assume


current decreases at a
constant rate. Then
Vo=Vs+VL
To ensure continuous current
flow, a capacitor is included.

Performance of a step up converter with resistive load (C=0).

DC-DC Converter classification


First

quadrant converter

Second

quadrant
converter

1st

and 2nd quadrant


converter

3rd

and 4th quadrant


converter

Four

quadrant converter

Second Quadrant Converter

1-2 and 3-4 quadrant converters


1st quad: S1, D4
2nd quad: S4, D1

3rd quad: S3, D2


4th quad: S2, D3
Polarity of the load EMF is
reversed.

Four quadrant converter

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