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DC to DC ConvertersUsually use transistors as switches
Act as a DC transformer
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Buck Converter
• Step down converter
• Switch
• Low-pass LC filter
• Diode
• Continuous conduction
• Discontinuous current
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Buck Converter Analysis
• �� = �� = ����; D = switch duty ratio
• ∆�=
��� − �� �� =
�� 1 − � �
• � = �� =��
�
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Example
• In Buck converter, L = 24µF (steady-state): Vin = 20V; D = 0.6;
Po = 14V; fs = 200 kHz. Calculate and draw the waveform.
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Boost Converter
• Step-up
• Same components
• Different topology!
• See stages of operation
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Boost Converter
• ∆�=
��� �� =
(�� − ���) 1 − � �
•��
���=
��
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Example
• Consider a boost converter, the inductor current has ΔiL=2 A.
Vin = 5 V, Vo = 12 V, Po = 11 W, fs = 200 kHz. Calculate L and
draw the waveform.
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Control of DC to DC Converter
• Error voltage = desired – actual
• Controller: Control duty cycle (PID)
• Modulator
• Entire controller is available as an IC.
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Switch, PWM, Electronics, Reference, and Buck Converter
(LM2529: Courtesy of National Semiconductors)
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LM2585 with Boost RegulatorNational Semiconductors
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Flyback Converter(Isolated Power Converter)
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Pulse Width Modulator
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DC Motor Quadrant
• First: Steady-State forward driving.
• Fourth: Regenerative breaking; machine trying to slow down; like breaking
for traffic light.
• Third: Reverse steady-state driving.
• Second: Regenerative breaking.
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Half-Bridge DC Chopper
• Buck converter: Motoring
• Boost Converter: Generating
• Two quadrant operating capability
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Full-Bridge DC Chopper
• Full-Quadrant Operation
• T1 and T2 ON: + Output voltage
• T3 and T4 ON: - Output voltage
• DC current and torque: + and –
• DC voltage and speed: + and –
• All quantities can be positive or negative
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Summary of DC Choppers
• One Quadrant
• Half Bridge
• Full Bridge