Q&A(FAQ) Cautions for Series Operation of SMPS with Synchronous Rectification.
When operating power supplies that use synchronous rectification in the secondary-side rectifier circuit in series, special caution is required.
1. Synchronous Rectification
Synchronous rectification is a type of circuit topology used to improve efficiency, and it is generally applied to the rectification circuit on the secondary side. MOSFETs are used for rectification instead of diodes.
2. Behavior in Series Operation When One Power Supply Shuts Down
When one power supply in a series configuration shuts down, the synchronous rectification MOSFET in that unit turns OFF. The operating power supply continues to generate output current, which then flows through the body diode of the MOSFET in the shut-down power supply.
The forward voltage (Vf) of the MOSFET body diode is approximately 0.7 to 1.3 V, resulting in higher power dissipation than during normal operation. This increased power loss may lead to thermal stress or component damage.
To prevent this issue, it is recommended to install a Schottky barrier diode, which has a lower forward voltage (Vf), between the output terminals.
For details of the product's circuit topology, please contact us.