UC2851DW

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The UC2851DW is a primary-side, pulse-width modulation (PWM) control device. It can be applied in off-line power supplies such as non-isolated AC/DC converters, offline switches, and traditional converter/charger applications. It encompasses critical functions for cost-effective power supplies such as primary control, feedback sense and device protect.

The UC2851DW is designed to provide fixed-frequency peak-current-mode PWM control without any additional external loop-compensation components, making it easy to design a power supply. The device features an internal soft-start of typically 4 ms for each startup operation and an adjustable line under voltage (UV) detection. It also includes an adjustable-frequency oscillator whereby the frequency can be set from 50 kHz to 1 MHz to optimize the system performance such as minimum audible noise (Require improvements in technology keeps getting better).

The UC2851DW offers enhanced safety-and-protection features. Its sense circuitry can limit primary current, monitor output voltage, and detect open load and short circuit conditions, including arc fault detection. External components can also be used to detect over temperature and to enable latch mode.

The UC2851DW exhibits excellent features and wide performance range making it fully suitable for off-line power supplies with minimum development time and cost. Its proven functions and wide performance range provides a complete and robust design solution.

The input voltage range of the UC285DW is 85-265VAC and its maximum output current is 6.5A. The UC2851DW also features a frequency jittering circuit which prevents injection of too-high-amplitude high-frequency components into the input mains in order to comply with conducted EMI regulations. It also provides selectable linear and PWM dimming from 100-0% brightness.

The working principle of the UC2851DW is simple. It operates in peak current-mode control and its internal high-gain loop-control provides fast response and good transient performance. The peak primary current is determined by voltage differences between its internal reference voltage (Vref) and its peak current monitoring (COMP) pins. The Vref is a precision reference voltage with a typical value of 0.8V. The COMP voltage can be supplied by external voltage source, normal current sense resistor, or open-loop current recall feature. The COMP voltage represents the sensed primary current.

The internal logic circuitry of the UC2851DW is designed to ensure low power dissipation, small area and high reliability. It features separate disable, standby and PWM control signals which provide maximum flexibility and control for the external devices and components. Additionally, its integrated fault-signal generator and integrated MOSFET output driver do not require additional external components.

In conclusion, the UC2851DW is a highly reliable, cost-effective and versatile pulse-width modulation controller for off-line power supplies such as AC/DC converters, offline switchers, and traditional converter/charger applications. It offers excellent features and wide performance range making it fully suitable for developing low-cost off-line power supplies.

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