FSFR1800HS

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PMIC - AC DC Converters, Offline Switchers include a variety of power conversion technologies to convert alternating current (AC) to direct current (DC), store and regulate it, and switch the converted power. One of the popular offline switchers is the FSFR1800HS. This application note explains its application field and working principle.

FSFR1800HS is a flyback offline switcher IC with 800V/1.8A on-chip MOSFET. It is optimized for use in small, low-cost, off-line power supply applications and can operate in both constant voltage (CV) and constant current (CC) modes. It features all necessary safety protections and is compliant with international energy efficiency and safety regulations. For example, it meets the requirements of the international energy efficiency standard IEC62368-1 safety standard and UL/CUL class B EMI compliance. The power conversion efficiency is up to 85%.

The FSFR1800HS is suitable for a wide range of applications including offline AC-DC switchers, line operated/battery chargers, utility/inverter, AC-DC auxiliary supplies, and high-voltage DC/DC power supplies. It offers several features that make it very convenient. It provides a pulse-by-pulse over current protection (OCP) to limit the primary peak current as well as soft start and pre-bias start to reduce the peak current surges and the inrush current during power-up. It also offers various protections, such as over voltage protection (OVP), under voltage lock-out (UVLO), short circuit protection (SCP), frequency jittering at light load, and auto-restart.

The working principle of the FSFR1800HS can be divided into four parts:

• Supply and control circuit: This circuit consists of power supply input, power on reset circuit, error amplifier and voltage reference circuit. The power on reset circuit is used to ensure the FSFR1800HS is correctly latched, and the error amplifier provides feedback control of the output voltage to allow current sharing between output devices.
• Timing control circuit: The FSFR1800HS can provide various protections, over current protection (OCP), over voltage protection (OVP) and under voltage lock-out (UVLO). The time control circuit will compare the voltage feedback, voltage thresholds and turn on/off the gate signal.
• MOSFET driver: This circuit provides a drive current which controls the MOSFET converter to transfer electrical energy from input voltage to output voltage.
• MOSFET converter: An on-chip MOSFET converter connected to the primary winding of an isolation transformer. The converter is controlled by the gate signal to convert AC power to DC power and provide it to the load.

In summary, the FSFR1800HS is a flyback offline switcher IC with 800V/1.8A on-chip MOSFET. It can be used in a wide range of applications, such as offline AC-DC switchers, line operated/battery chargers, utility/inverter, AC-DC auxiliary supplies and high-voltage DC/DC power supplies. The working principle involves four circuits: Supply and control circuit, timing control circuit, MOSFET driver and MOSFET converter, which work together to control the transfer of electrical energy from input voltage to output voltage.

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