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DC DC Converters 1
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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
VRMS=k1/2Vs
Pout=(kVs2)/R
k=ton/T is the duty cycle
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 converters1st 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