UC3861NG4

The UC3861NG4 is a high performance off-line Switcher control IC with an integrated oscillator and overload protection. It is used in off-line power supply applications like AC/DC converters and adapters. The integrated overload protection provides additional device protection in the event of a short-circuit.

The UC3861NG4 application field includes building various AC/DC power supply convertors such as LCD TV, laptop and other consumer products with advantages like high efficiency, low cost and low standby power.

This device integrates a number of features that make it suitable for a wide range of applications. The features include:

• Single Chip Controller for AC/DC Conversion
• High efficiency: up to 90%
• Low cost and low standby power
• Integrated over voltage protection
• Integrated low power/ frequency fold-back for efficient conversion at light load

The basic working principle of the UC3861NG4 consists of two main sections, an oscillator and a PWM output stage. The oscillator produces a sawtooth waveform at the operating frequency which is determined by the value of the external components, the power supply and the operating temperature.

The PWM output stage converts the sawtooth waveform into a square wave, which is then converted into high frequency pulses to drive the power switch. The output frequency can be modulated by varying the charging current of the sawtooth waveform capacitor. The output voltage is controlled by the voltage feedback loop.

The UC3861NG4 contains several advanced features that improve its overall performance. These features include internally compensated voltage loop, soft start, frequency jittering, programmable undervoltage lockout, programmable minimum on-time, and burst mode operation.

The UC3861NG4 is a highly versatile device for AC/DC and offline power supply applications. It provides excellent system efficiency, low cost and low standby power, with integrated protection features for improved system performance and reliability.