POWER ELECTRONICS – PAGE 3
Half Wave Rectifier with RL Load
1️⃣ Circuit Concept
In an RL load, the inductor changes the output waveform behavior.
- R → Limits current
- L → Opposes sudden change in current
- Diode → Conducts only in forward bias
2️⃣ Working Principle
Positive Half Cycle (0 to π)
- Diode is forward biased
- Current flows through R and L
- Output voltage follows input
Important: Because of inductance, current does NOT immediately drop to zero at π.
Energy stored in the inductor keeps current flowing.
After π (π to β)
- Input becomes negative
- Inductor tries to maintain current
- Diode continues conduction
- Current gradually reduces to zero at angle β
β = Extinction Angle
3️⃣ Output Waveform Characteristics
Voltage:
- 0 to π → Same as input
- π to β → Decaying behavior
- After β → Zero
Current:
- Lags voltage
- Continues beyond π
- Smoother waveform
4️⃣ Important Equations
Input Voltage:
v = Vm sin(ωt)
Differential Equation:
Vm sin(ωt) = Ri + L (di/dt)
General Current Solution:
i(t) = Im sin(ωt − φ) + C e−Rt/L
φ = tan−1(ωL / R)
5️⃣ Key Observations (Exam Important)
- ✔ Conduction angle > 180°
- ✔ Current does not fall suddenly
- ✔ Ripple reduced
- ✔ Better output than pure R load
- ✔ Power factor decreases
6️⃣ Comparison: R Load vs RL Load
| Parameter | R Load | RL Load |
|---|---|---|
| Conduction | 180° | > 180° |
| Current Drop | Sudden | Gradual |
| Ripple | High | Lower |
| Power Factor | Better | Lower |
GATE / PSU Focus: Extinction angle calculation, Differential equation solving, Average voltage, RMS current, Power factor.
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