UNITRODE UC1852, UC2852, UC3852 Technical data

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

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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.

UC1852

UC2852

CONNECTION DIAGRAM

UC3852

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<Ta<+125°C for the UC1852, –40°C<Ta<+85°C for the UC2852, and 0°C<Ta<+70°C for the UC3852, and Ta=Tj.

PARAMETER	TEST CONDITIONS	MIN.	TYP.	MAX.	UNITS
Timer Section
ISET Voltage		4.5	5.0	5.5	V
RAMP Charge Current	RAMP=2.5V	88	98	108	μA
RAMP Discharge Current	ISNS= –1.0V, RAMP=1.0V	12	28	50	mA
RAMP Saturation Voltage	ISNS= –1.0V, IRAMP=100μA		0.006	0.200	V
RAMP Threshold - Maximum Frequency	VFB=10V, COMP open	0.92	1.02	1.12	V
RAMP Threshold - PWM Comparator		3.9	4.3	4.8	V
Current Sense Comparator
ISNS Restart Threshold		–18	–10	–4	mV
ISNS Fault Threshold		–550	–450	–350	mV
ISNS Input Current		–100	–30	100	μA
Error Amplifier Section
VFB Input Voltage		4.6	5.0	5.3	V
VFB Input Bias Current		–5.00	–0.03	5.00	μA
COMP Sink Current	COMP=7.5V	10			mA
COMP Source Current	COMP=2.5V	–300	–175	–100	μA
COMP Clamp Voltage	VFB=0.0V, COMP open	9.2	10.0	10.6	V
OUT Output
OUT Saturation Voltage High	VCC=13V, IOUT= –200mA, RAMP=2V	0.5	1.7	2.5	V
OUT Saturation Voltage Low	IOUT=200mA, ISNS= –1.0V	0.5	1.6	2.2	V
OUT Saturation Voltage Low @ 10mA	IOUT=10mA, ISNS= –1.0V		0.05	0.40	V
OUT Clamp Voltage	IOUT= –200mA, RAMP=2V	10.0	12.0	14.5	V
OUT Voltage during UVLO	IOUT=100mA, VCC=0V	0.5	1.0	2.2	V
Overall Section
Inactive Supply Current	VCC=10V	0.2	0.4	1.0	mA
Active Supply Current		3.0	6.0	10.0	mA
VCC Clamp Voltage	ICC=25mA	30	33	36	V
VCC Turn-On Threshold		14.5	16.3	17.5	V
VCC Turn-Off Threshold		10.5	11.5	13.0	V
VCC Threshold Hysteresis		3	5	7	V

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