UC3852N

UC1852 UC2852 UC3852 High Power-Factor Preregulator FEATURES • Low-Cost Power Factor Correction • Power Factor Greater Than 0.99 • Few External Parts Required • Controlled On-Time Boost PWM • Zero-Current Switching • Limited Peak Current • Min and Max Frequency Limits • Starting Current Less Than 1mA • High-Current FET Drive Output • Under-Voltage Lockout DESCRIPTION The UC1852 provides a low-cost solution to active power-factor correction (PFC) for systems that would otherwise draw high peak current pulses from AC power lines. This circuit implements zero-current switched boost conversion, producing sinusoidal input currents with a minimum of external components, while keeping peak current substantially below that of fully-discontinuous converters. The UC1852 provides controlled switch on-time to regulate the output bulk DC voltage, an off-time defined by the boost inductor, and a zero-current sensing circuit to reactivate the switch cycle. Even though switching frequency varies with both load and instantaneous line voltage, it can be maintained within a reasonable range to minimize noise generation. While allowing higher peak switch currents than continuous PFCs such as the UC1854, this device offers less external circuitry and smaller inductors, yet better performance and easier line-noise filtering than discontinuous current PFCs with no sacrifice in complexity or cost. The ability to obtain a power factor in excess of 0.99 makes the UC1852 an optimum choice for low-cost applications in the 50 to 500 watt power range. Protection features of these devices include under-voltage lockout, output clamping, peak-current limiting, and maximum-frequency clamping. The UC1852 family is available in 8-pin plastic and ceramic dual in-line packages, and in the 8-pin small outline IC package (SOIC). The UC1852 is specified for operation from -55°C to +125°C, the UC2852 is specified for operation from -40°C to +85°C, and the UC3852 is specified for operation from 0°C to +70°C. TYPICAL APPLICATION UDG-92001 10/94 UC1852 UC2852 UC3852 CONNECTION DIAGRAM ABSOLUTE MAXIMUM RATINGS Supply Voltage (Low-impedance Source)..........................30.0V Supply Current (High-impedance Source) ......................30.0mA OUT Current, Peak .............................................................±1.0A OUT Energy, Capacitive Load............................................ 5.0µJ Input Voltage, ISNS ............................................................±5.0V Input Voltage, VFB............................................. –0.3V to +10.0V COMP Current ...............................................................±10.0mA ISET Current..................................................................–10.0mA Power Dissipation at Ta≤25°C (Note 3) ..............................1.0W Storage Temperature ....................................... –65°C to +150°C Lead Temperature (Soldering, 10 Seconds) ................... +300°C Note 1: All voltages with respect to GND (Pin 1). Note 2: All currents are positive into the specified terminal. Note 3: Refers to DIL-8 Package. Consult Packaging Section of Unitrode Integrated Circuits databook for thermal limitations and considerations of package. DIL–8 (TOP VIEW) SOIC–8 (TOP VIEW) J or N Package D Package UDG-92002 ELECTRICAL CHARACTERISTICS Unless otherwise stated, VCC=24V, ISET=50kΩ to GND, RAMP=1nF to GND, ISNS= –0.1V, VFB connected to COMP, no load on OUT, –55°C