What is a Synchronous Rectifier Controller?

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Editorial Team - everything PE

May 22, 2024

A Synchronous Rectifier Controller is an electronic device that enhances the efficiency of power conversion circuits. It is used in switch-mode power supplies (SMPS) and other DC-DC converters by replacing traditional diode rectifiers with actively controlled MOSFETs (metal-oxide-semiconductor field-effect transistors). The MOSFET’s turn on and off can be controlled to be synchronized with the diode’s conduction. These synchronous rectifier (SR) MOSFETs have lower voltage drops and conduction losses than traditional diodes.

Synchronous RectificationKey features of Synchronous Rectifier Controller

  • MOSFET Control: The primary function of a synchronous rectifier controller is to drive MOSFETs instead of diodes. MOSFETs, when properly controlled, exhibit much lower forward voltage drops, resulting in reduced conduction losses and improved efficiency.
  • Timing and Synchronization: The controller precisely times the switching of the MOSFETs to ensure they turn on and off at the correct intervals, synchronized with the switching of the primary side of the converter. This timing is crucial to ensure that the MOSFETs act as low-resistance paths during the conduction phase and are turned off to block reverse currents during the non-conduction phase.
  • Efficiency Improvement: By using MOSFETs instead of diodes, synchronous rectification can significantly reduce power losses, especially at lower output voltages where the diode forward voltage drop represents a larger proportion of the total voltage.
  • Protection Features: Synchronous rectifier controllers often include protection mechanisms such as over-current protection, under-voltage lockout, and thermal shutdown to safeguard the MOSFETs and ensure reliable operation.

Synchronous rectifier controllers are commonly used in SMPS, DC-DC converters, battery chargers, and power adapters.

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