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. …
