Typical Application Notes
The UC1852 provides a low-cost active power factor correction (PFC) solution for systems that extract high peak current pulses from AC power lines. The circuit implements a zero-current switching boost conversion, producing a sinusoidal input current with minimal external components, while keeping the peak current much lower than that of a fully discontinuous converter.
The UC1852 provides controlled switch on-time to regulate the output bulk DC voltage, off-time defined by the boost inductor, and a zero-current sense circuit to reactivate the switching cycle. Even if the switching frequency varies with load and instantaneous line voltage, it can be kept within a reasonable range to minimize noise generation.
While allowing higher peak switching currents than continuous PFCs such as the UC1854, the device offers less external circuitry and smaller inductors, but better performance and easier line noise filtering than discontinuous current PFCs, There is no sacrifice of complexity or cost. The ability to obtain a power factor in excess of 0.99 makes the UC1852 the best choice for low-cost applications in the 50 to 500 watt power range. Protection features of these devices include undervoltage lockout, output clamp, peak current limit and maximum frequency clamp.
The UC1852 series is available in 8-pin plastic and ceramic dual in-line packages and 8-pin small outline integrated circuit packages (SOIC). The UC1852 is suitable for operation from -55°C to + 125 °C, the UC2852 is suitable for operation from -40°C to +85°C, and the UC3852 is suitable for operation from 0°C to +70°C.

5.0 µg input voltage, ISNS
Input Voltage, VFB………..0.3V to +10.0V
Compensation current
ISET current - 10.0mA power consumption at Ta≤25°C (Note 3) ………… 1.0W
Storage temperature…………-65°C to +150°C
Lead Temperature (Soldering, 10 sec) ...... +300°C Note 1: All voltages related to GND (Pin 1).
Note 2: All currents are positive flowing into the designated terminals.
Note 3: Refer to DIL-8 package. Refer to the Packaging section of the Unitrode IC data sheet for thermal limitations and considerations for packaging.
Electrical Characteristics Unless otherwise noted, VCC=24V, ISET=50 kΩ to ground, RAMP=1 nF to ground, ISNS=
–0.1V, VFB to compressor, no-load output, –55°C

Pin Description Compensation: COMP is the output of the error amplifier and the input of the PWM comparator. To limit the PWM on time, this pin is clamped to approximately 10V. To achieve soft-start, the COMP pin can be pulled low and raised together with the PNP transistor, capacitor, and resistor.
Ground: Ground for all functions goes through this pin.
Iset: The primary function of this pin is to program the ramp charge current. The ramp charge current is about 5V divided by the external resistor from ISET to ground. Resistors in the 10kΩ to 50kΩ range are recommended, producing currents in the 100µA to 500µA range.
The second function of ISET is as a reference output. The ISET pin is typically regulated to 5V±10%. It is important that this pin only sees the load of the ramp programming resistor, but a high input impedance comparator or amplifier can be connected to this pin or the wiper on the ramp programming resistor if desired.
The third function of the ISET pin is as a fault output. In the event of an overcurrent fault, the ISET pin is forced to approximately 9V by the fault comparator. This can be used to trip an external protection circuit to disable the load or initiate a fault restart cycle.
ISNS No.: The inputs of the zero-current comparator and the over-current comparator are specially designed to allow operation within a ±5V dynamic range. In noisy systems or systems with very high-Q inductors, the signal input to the ISNS needs to be filtered to prevent premature restarts or fault cycling. For best accuracy, ISNS should be connected through a current sense resistor of no more than 200 ohms.
Out: The output of a high-current power driver capable of driving the gates of power MOSFETs with peak currents in excess of ±500mA. To prevent damage to the power MOSFETs, the output pins are internally driven by a 12V supply. However, lead inductance between the output pin and the load can cause overshoot and ringing. An external current boost transistor will increase this overshoot and ringing. If there is any appreciable distance between the IC and the MOSFET, external clamping diodes and/or series damping resistors may be required. OUT is low when VCC is below the UVLO threshold.
Ramp: Controlled real-time PWM requires a timer whose time can be modulated by an external voltage. The timer current is programmed by a resistor from ISET to GND. A ramp-to-ground capacitor in combination with boost compensation sets the on-time. The recommended value of the timer capacitor is between 100pF and 1nF.
VCC: VCC is the logic and control power connection for this device. The VCC current is the sum of the active device supply current and the average output current. Knowing the maximum operating frequency and the MOSFET gate charge (QG), the average output current can be estimated by:
IOUT=Qg×F
To prevent noise problems, bypass VCC to ground with a ceramic and electrolytic capacitor.
Ventricular Fibrillation: VFB is the error amplifier inverting input. This input is used as the voltage sense input of the error amplifier

Application Information: 100 Watt Power Factor Preregulator

Marketing status values are defined as follows:
Active: Recommended product equipment for new designs.
Lifeboat: Texas Instruments has announced that the device will be discontinued and a lifetime purchase period is in effect.
No.: Not recommended for new designs. The device supports existing customers in production, but TI does not recommend using this part in new designs.
Preview: The device has been released, but not yet in production. The sample may or may not have it. Obsolete: TI has discontinued production of this device.
Eco Plan - Planned eco-friendly classification: Lead Free (RoHS), Lead Free (RoHS Exempt) or Green (RoHS & Sb/Br Free) - Please check /product content for the latest availability information and other product content details.
Pending: No lead-free/green transition plan defined.
Lead-Free (RoHS): The term "lead-free" or "lead-free" for titanium refers to semiconductor products that are compatible with current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in a homogeneous material. If designed for high temperature soldering, titanium-lead-free products are suitable for specified lead-free processes.
Lead-Free (RoHS Exempt): This assembly is RoHS exempt for 1) lead-based flip-chip solder joints used between the die and the package, or 2) lead-based die adhesives used between the die and the leadframe. As defined above, this component is considered lead-free (RoHS compliant).
Green (RoHS and Sb/Br free): TI defines "green" as lead free (RoHS compliant), free of bromine (Br) and antimony (Sb) flame retardants (Br or Sb in homogeneous material with no weight by weight) more than 0.1%)
MSL, maximum temperature. -- Moisture sensitivity rating according to JEDEC industry standard classification and peak solder temperature.
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