Page 61 – SEPIC Converter (Design Example + Component Selection)
Subject: Power Electronics
Level: GATE / PSU + Practical Design
🔹 1️⃣ What is SEPIC?
SEPIC = Single-Ended Primary Inductor Converter ✔ Non-inverting output ✔ Can step-up or step-down ✔ Continuous input current ✔ Widely used in battery-powered systems
Voltage Gain (CCM):
Vo / Vin = D / (1 − D)
🔹 2️⃣ Design Problem
Design a SEPIC converter with:
Vin = 12 V
Required Vo = 24 V
Load Power = 48 W
Switching Frequency fs = 50 kHz
Allow ripple current = 30% of average current
🔹 3️⃣ Step 1 – Duty Cycle
Vo/Vin = D/(1−D) 24/12 = D/(1−D) 2 = D/(1−D) 2(1−D) = D 2 − 2D = D 2 = 3D D = 0.667
🔹 4️⃣ Step 2 – Output Current
Io = P / Vo = 48 / 24 = 2 A
🔹 5️⃣ Step 3 – Inductor Design
Average input current:
Pin ≈ Pout Iin = P / Vin = 48 / 12 = 4 A
Allow 30% ripple:
ΔIL = 0.3 × 4 = 1.2 A
Inductor formula:
L = (Vin × D) / (ΔIL × fs)
L = (12 × 0.667) / (1.2 × 50000) = 8 / 60000 = 133 μH
Choose: L1 = L2 ≈ 150 μH (standard value)
🔹 6️⃣ Step 4 – Coupling Capacitor (C1)
Approximation formula:
C1 ≥ Io × D / (ΔVc × fs)
Assume allowed ripple ΔVc = 1 V
C1 = (2 × 0.667) / (1 × 50000) = 1.334 / 50000 = 26.6 μF
Select: 33 μF
🔹 7️⃣ Step 5 – Output Capacitor
Co ≥ Io × D / (ΔVo × fs)
Assume ripple 0.5 V
Co = (2 × 0.667) / (0.5 × 50000) = 1.334 / 25000 = 53 μF
Select: 68 μF
🔹 8️⃣ Final Design Summary
| Parameter | Value |
|---|---|
| Duty Cycle | 0.667 |
| Inductors | 150 μH |
| C1 | 33 μF |
| Co | 68 μF |
Exam Memory Capsule
✔ SEPIC gain = D/(1−D) ✔ Non-inverting output ✔ Two inductors ✔ Design based on ripple percentage ✔ Very common in battery & automotive systems
Advanced DC-DC Design Series – Shaktimatha Learning
.png)
No comments:
Post a Comment