Flyback Converter Calculator
Calculate flyback converter turns ratio, peak primary and secondary currents, and power levels for isolated DC-DC converter design.
Formula
N = \frac{V_{in} \cdot D}{V_{out}(1-D)},\quad I_{p,peak} = \frac{2 I_{in}}{D}
Reference: Unitrode Power Supply Design Seminar SEM600
How It Works
A flyback converter is a type of switched-mode power supply that uses a transformer to store and transfer energy between input and output circuits. During the switch's on-time, energy is stored in the transformer's magnetizing inductance, and during the off-time, this stored energy is transferred to the output. This topology allows for efficient voltage conversion and galvanic isolation.
Worked Example
Problem: Design a flyback converter with Vin = 12V, Vout = 5V, switching frequency fs = 100 kHz, duty cycle D = 0.4, and diode forward voltage VD = 0.7V Solution: 1. Calculate turns ratio N: N = (12V · 0.4) / ((5V + 0.7V) · (1 - 0.4)) = 2.14 2. Calculate peak input current: Iin = (5V · 1A) / 12V = 0.417A 3. Calculate peak primary current: Ipk = 2 · 0.417 / 0.4 = 2.085A 4. Calculate output power: Pout = 0.5 · Lm · (2.085)² · 100 kHz · (2.14)² = 5.14W
Practical Tips
- ✓Choose low-loss MOSFET with fast switching characteristics
- ✓Use Schottky diodes for lower forward voltage drop
- ✓Implement adequate thermal management
- ✓Select magnetic core material with high permeability
Common Mistakes
- ✗Neglecting diode forward voltage drop in calculations
- ✗Incorrect estimation of magnetizing inductance
- ✗Not accounting for transformer core saturation
- ✗Overlooking parasitic resistances and capacitances
Frequently Asked Questions
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