UC3879DWG4

UC3879DWG4 Application Field and Working Principle

The UC3879DWG4 is a pulse Width Modulated (PWM) controller with a wide range of operating voltages and deadtimes, offering great flexibility for power conversion designs. This controller belongs to a type of DC-DC switching controllers, and its application field range from off-line Sepic, Cuk and Cc-Cuk topologies to flyback and Buck/Boost converters. This integrated IC devices requires additional external parts to control and regulate the power flow, as well as to protect the devices.

Overview

The UC3879DWG4 is an internally compensated PWM controller designed for off-line and dc-to-dc converter applications. It is designed to minimize the number of external components to simplify the power conversion designs, utilizing a high frequency quasi-resonant current mode control scheme. It can provide line under-voltage protection and also provides continuous current limiting and thermal shutdown. The UC3879DWG4 is optimized for when driving MOSFETs in applications requiring two-level switching under PWM control. It features an operating frequency range up to 250 kHz, which allows it to be used in a wide range of flyback, Sepic and BuckBoost converters. It also features additional logic level functionality to control external MOSFETs.

Application Field

The UC3879DWG4 is suitable for a wide range of off-line and dc-to-dc converter applications including:

• SEPIC
• Cuk and Cc-Cuk
• Flyback
• Buck
• Buck-Boost

The UC3879DWG4 can also be used for controlling power supplies for off-line, telecommunication and industrial applications. Its wide operating range and low quiescent current make it ideal for cost effective power solutions.

Working Principle

The UC3879DWG4 utilizes an internal oscillator, high frequency quasi-resonant current mode control, synchronous rectification and low start-up current to provide a high performance power conversion solution. The IC can be operated in an extended operating frequency range up to 250kHz, which allows designers to use the right frequency to optimize transient response, power resolution and efficiency. This frequency range makes this IC suitable for a wide range of conversion applications. It also features logic level enable, frequency adjust and deadtime controls.

The IC features an Adaptive Off Time Control (AOTC) circuit that provides a constant peak current limit, improving power supply performance and efficiency. The AOTC monitors the voltage across the load and adjusts the off time accordingly. This help to protect the power supply from over-current and short-circuit conditions. The AOTC circuit also allows the device to operate in constant peak current mode with high loaded conversion efficiency. This AOTC is controlled by a frequency select pin that can be used to select between a fixed frequency setting or a variable frequency setting. The variable setting allows the user to adjust the operating frequency to optimize the performance of the power supply.

Finally, the UC3879DWG4 features an internal Brown-Out Detection (BOD). When the input supply voltage drops below the BOD threshold, the controller shuts down the power supply at the same time providing line under-voltage protection. This allows for better system protection during line transients and brown-outs.

The UC3879DWG4 provides the flexibility for designers to develop complicated power conversion designs. Its low quiescent current, wide operating range and wide power management features allows it to be used in a wide range of off-line and dc-to-dc converter applications.