Full wave rectifier; Full wave bridge rectifier

Full Wave Rectifier: Working, Circuit, Output & Waveforms

Rectifiers are essential circuits used to convert Alternating Current (AC) into Direct Current (DC). Compared to a Half Wave Rectifier, a Full Wave Rectifier provides higher average DC output with fewer ripples, making it more efficient for power supply applications.

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1. Full Wave Rectifier (Center-Tap Type)

Circuit Diagram

👉 Consists of:

• Two diodes (one for each half cycle)

• Center-tap transformer

• Resistive load (R)

When the AC input alternates:

• Positive half cycle → Diode D1 conducts.

• Negative half cycle → Diode D2 conducts.

• Current through the load flows in the same direction during both halves → producing DC.

📊 Waveform: Output has two pulses per AC cycle, giving smoother DC than half wave rectifier.

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2. Output Voltage of Full Wave Rectifier

$$V_{dc(avg)} = \frac{2V_{max}}{\pi} \approx 0.637 \, V_{max}$$ $$V_{rms} = \frac{V_{max}}{\sqrt{2}} \approx 0.707 \, V_{max}$$ $$V_{dc(avg)} \approx 0.9 \, V_{rms}$$

Where:

• $V_{max}$ = Peak value of AC input

• $V_{rms}$ = RMS value of AC input

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3. Disadvantages of Center-Tap Rectifier

• Requires a center-tapped transformer.

• Transformer must handle higher voltage rating → increases cost & size.

👉 To overcome this, the Bridge Rectifier is used.

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4. Full Wave Bridge Rectifier

Circuit Diagram

• Uses 4 diodes arranged in bridge form.

• Positive half cycle → D1 & D2 conduct.

• Negative half cycle → D3 & D4 conduct.

• Eliminates the need for center-tapped transformer.

✅ Advantage: Smaller, cheaper transformer requirement compared to center-tap type.

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5. Smoothing Capacitor in Full Wave Rectifier

Even after rectification, the output contains ripples.

To minimize ripples, a smoothing capacitor is connected across the load.

• Capacitor charges to peak voltage during diode conduction.

• Discharges slowly during non-conduction → giving smooth DC output.

Selection of Capacitor:

1. Working Voltage → Higher than rectifier’s no-load DC voltage.

2. Capacitance Value → Higher value reduces ripples.

   • Typically: 100 µF aluminum electrolytic capacitors are used.

📊 Waveform with capacitor: Ripple reduces → DC output closer to a straight line.

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6. Comparison: Half Wave vs Full Wave Rectifier

Feature	Half Wave Rectifier	Full Wave Rectifier
No. of diodes	1	2 (center-tap) / 4 (bridge)
Transformer requirement	No CT needed	CT needed (except bridge)
Average DC output	Vmax/π (0.318 Vmax)	2Vmax/π (0.637 Vmax)
Ripple frequency	Same as AC (50 Hz)	Double AC (100 Hz)
Efficiency	Low	Higher

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7. Applications of Full Wave Rectifier

• DC power supplies

• Battery charging circuits

• Radio, TV, amplifier circuits

• Welding and electroplating equipment

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✅ Key Takeaway:
A Full Wave Rectifier converts both halves of AC into DC, doubling efficiency compared to half wave. With a smoothing capacitor, ripple-free DC can be achieved, making it the preferred choice in power supply design.

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