Advanced Flyback Input Capacitor Calculator

Design optimal power supplies fast. Calculate bulk capacitance accurately now.

1. AC Input Specs

Example: 230 V (Universal range use 85 to 265).
Example: 50 Hz or 60 Hz.
Example: 0.7 to account for conduction time fraction.

2. Power & Efficiency

Example: 50 Watts.
Example: 12 V secondary rail.
Example: 85% conversion efficiency.

3. Ripple Constraints

Example: 25 V peak-to-peak voltage drop.
Example: 0.5 Ohms for thermal safety.
Example: 1.2 safety multiplier.

Comprehensive Guide to Flyback Input Capacitor Design

Designing a robust switched-mode power supply requires meticulous selection of the primary bulk input capacitor. This component filters rectified mains voltage and supplies stable DC energy during switch-off states and line dropouts. Incorrect sizing leads to excessive ripple, triggering brownout protection or overheating components.

Formula Used

The primary bulk capacitance is derived using the total input power and allowable voltage valley:

$$P_{in} = \frac{P_{out}}{\eta}$$

$$C_{in} = \frac{2 \cdot P_{in} \cdot t_{discharge}}{V_{peak}^2 - V_{min}^2}$$

Where $V_{peak} = V_{in,rms} \cdot \sqrt{2}$, and $t_{discharge}$ represents the capacitor discharge period defined by line frequency cycles and hold-up parameters.

How to Use This Calculator

Frequently Asked Questions

It stabilizes the DC bus voltage feeding the primary transformer winding, directly minimizing low-frequency output ripple and protecting switching transistors from excessive voltage spikes.

A low capacitance value causes deep voltage valleys, triggering undervoltage lockout loops or forcing excessive ripple current through electrolytic elements, drastically reducing their operational lifespan.

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