GATE Electrical Engineering - Complete Master Library

 

 POWER ELECTRONICS – PAGE 4

Half Wave Rectifier with Freewheeling Diode

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1️⃣ Why Freewheeling Di

ode?

In RL load rectifier, current continues beyond π due to inductor energy. This causes negative voltage and poor output quality.

Solution: Add a Freewheeling Diode (FWD) across the load.

                                           

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2️⃣ Circuit Concept

• Main diode → conducts during positive half cycle
• Freewheeling diode → provides path when supply becomes negative
• Inductor releases stored energy safely

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3️⃣ Working Principle

 0 to π (Positive Half Cycle)

• Main diode ON
• FWD OFF
• Output follows input

 π to 2π (Negative Half Cycle)

• Main diode OFF
• FWD ON
• Load current circulates through FWD
• Output voltage becomes zero (no negative portion)

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4️⃣ Output Waveform Features

• ✔ No negative voltage
• ✔ Ripple reduced
• ✔ Current smoother
• ✔ Better power factor
• ✔ Conduction limited to 180°

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5️⃣ Important Equations

Average Output Voltage:

V_avg = V_m / π

RMS Voltage:

V_rms = V_m / 2

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6️⃣ Advantages Over RL without FWD

Parameter	Without FWD	With FWD
Negative Voltage	Present	Eliminated
Ripple	Higher	Lower
Power Factor	Low	Improved
Output Quality	Poor	Better

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GATE / PSU Focus: Working comparison, waveform drawing, average voltage derivation, conceptual advantages.