This application note introduces how to use FAN103 and FSEZ13X7 to design primary-side regulated (PSR) flyback converter. This application note covers PSR concept, application scenarios, design guidance, circuit schematics and design examples.
This document serves as a design guideline for creating primary-side regulated (PSR) flyback converters, specifically utilizing the Fairchild Semiconductor FAN103 PWM PSR controller and the FSEZ13X7 Power Switch (EZ-PSR). It addresses the challenges of meeting international energy efficiency regulations for portable electronics chargers by eliminating secondary-side sensing components.
The note details the operation principles of PSR in discontinuous conduction mode (DCM) and provides a step-by-step design procedure. Key topics include estimating efficiencies for various operating points, designing the transformer to ensure DCM operation across the full load range, and implementing constant-current/constant-voltage control strategies.
| Supply Voltage (Vpp) Operation Range | 5V up to 24V |
|---|---|
| Frequency Reduction Activation Threshold | 70% of nominal output voltage |
PSR alleviates the burden of achieving energy efficiency regulations by removing output current sensing loss and eliminating all secondary-feedback circuitry.
Discontinuous conduction mode (DCM) is preferred for primary-side regulation since it allows better output regulation.
The converter uses a frequency reduction function that extends the switching period when the output voltage drops below 70% of its nominal value.