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.