POWER ELECTRONICS – PAGE 8
Half Wave Controlled Rectifier (Using SCR)
1️⃣ Introduction
A Half Wave Controlled Rectifier uses an SCR to control output voltage by varying the firing angle (α).
2️⃣ Circuit Operation
🔵 Positive Half Cycle
- SCR is forward biased
- It conducts only when gate pulse is applied
- Conduction starts at firing angle α
🔴 Negative Half Cycle
- SCR is reverse biased
- No conduction
3️⃣ Output Voltage Expression
Vavg = (Vm / 2π) (1 + cos α)
Where:
- Vm = Maximum input voltage
- α = Firing angle (in radians)
4️⃣ Important Observations
- α = 0° → Maximum output
- α = 90° → Reduced output
- α = 180° → Zero output
5️⃣ Waveforms
- Input: Sinusoidal
- Output: Controlled positive half cycle
- Conduction from α to π
6️⃣ GATE Exam Focus
- Derivation of average voltage
- Effect of firing angle
- Waveform identification
- Numerical problems on α variation
Very Important: Always convert α into radians in formula.
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