FIT0471

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FIT0471 is a type of evaluation board designed to meet the requirements of high efficiency, power factor corrected (PFC) front-end offline concepts. This device is used for non-isolated single and multiple output switch mode power supplies (SMPSs). The power supply employs a current mode PFC control IC and two MOSFETs in a half-bridge topology.

The control ICs feature a high voltage startup circuit and precise current sensing. The main purpose of the FIT0471 evaluation board is to study the features and performance of the ICs, such as power factor correction, harmonic management, and overload protection.

The evaluation board has a built-in isolated 400V/2A linear transformer and capacitor array. The switching frequency is externally adjustable by the user. In addition, the LM25017 controller has built-in soft start and over-voltage protection.

The working principle of the FIT0471 is based on a half-bridge topology. The main power devices are two MOSFETs (Q1 & Q2) connected in a half-bridge configuration. The operation of the system is controlled by the LM25017 primary side PFC controller. The FIT0471 can achieve an efficiency of 88% or greater.

The system starts when the power switch (S1) is on. When the power-on voltage reaches a certain value, the LM25017 control IC charges the internal start-up capacitor (C16). This causes U1 to start oscillating and turning on Q1 in a fixed frequency. Q1 conducts for the duration of one constant cycle, and then turns off. This causes the chip to discharge the startup capacitor C16, which results in the turn off of U1 and Q1.

When the switch S1 is closed, it will connect the input voltage to the LM25017 IC\'s internal supply. This will activate the PWM controller and the output voltage is set to the same as the programmed output voltage level. The output voltage is then regulated with a feedback loop. The switching frequency is regulated to 400KHz to ensure high efficiency, and the transformer resonant frequency is adjusted to minimize EMI.

The FIT0471 is designed to demonstrate the feasibility of high efficiency and power factor corrected offline concepts. The board is suitable for academic study, research and development, as well as for rapid prototyping. The board has several features such as built-in isolated transformer, precise current sensing, and high voltage operation, and is designed to meet the highest performance and quality criteria.

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