LNK457DG

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The LNK457DG is part of the forty-seven wide family of Primary Side Controller Integrated Circuit (CISC) devices from Linear Technology. This particular device is a member of Linear’s PMIC - LED Drivers which features high-output current, buck regulator topology as well as integrated current sense, boost/buck regulator and lighting control The LNK457DG is a flexible IC which is well suited for driving Light Emitting Diodes (LEDs). It is mainly used in LED lighting applications and the main features of this part include 16V to 300V input range, high-frequency buck control, low parts count and single stage current sense feedback. It is suitable for AC input applications as well as DC input supplies making it mainly useful for LED lighting applications. The main features of the LNK457DG include the fact that it is a low-cost, low-noise and highly efficient current-mode secondary-side controller for buck regulators. It offers a peak current mode control with a digital host interface for dimming, programming and diagnostic capability. The device also supports a wide input voltage range (16V to 300V) and provides additional protection features such as over-current, soft-start, open loop/overvoltage protection and a programmable reference voltage.The LNK457DG operates on the principal that when an input current is passed through a coil, an output current of greater magnitude is generated across an inductor. This greater magnitude is often referred to as a “flyback” current.The device has several main components which include a primary side driver IC, a floating secondary side driver IC, and other additional components such as protection circuits and sense transformers. The primary side driver IC is responsible for sensing the coil current and driving the primary side of the transformer with a suitable waveform. The floating secondary side driver IC, which is supplied by the primary side driver IC, senses the current flowing in the LED string, rectifies it and drives the LED load with the appropriate waveforms.The LNK457DG also offers integrated protection features such as over-current, soft-start, open loop/overvoltage protection and a programmable reference voltage. Additionally, it features an indicator pin and thermal shutdown, which protects the IC from destruction due to excessive temperature rise.In order to utilize the LNK457DG LEDs must be connected in series and in order to achieve the desired brightness level, the duty cycle of the current passing through the LED string must be varied. This is accomplished through the use of pulse width modulation (PWM). The duty cycle of the PWM signal can be directly adjusted by the output current setting. The main working principle of the LNK457DG is to vary the duty cycle of the current passing through the LED string and the primary side of the transformer in order to achieve the desired brightness level. By controlling the duty cycle, the output current impedance is varied and the output voltage at the LED load is adjusted accordingly. The output current set point is determined by the reference voltage. Overall, the LNK457DG is a great integrated circuit which offers a low-cost, low-noise and highly efficient current-mode secondary-side controller for buck regulators. It is mainly used in LED lighting applications and it enables adjustable brightness levels in order to achieve the desired effect. The device also offers several integrated protection features which make it an ideal choice for a wide variety of applications.

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