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Controls Boost PWM to Near Unity
Power Factor
Fixed Frequency Average Current
Mode Control Minimizes Line Current
Distortion
Built-in Active Snubber (ZVT) allows
Operation to 500kHz, improved EMI
and Efficiency
Inductor Current Synthesizer allows
Single Current Transformer Current
Sense for Improved Efficiency and
Noise Margin
Accurate Analog Multiplier with Line
Compensator allows for Universal
Input Voltage Operation
High Bandwidth (5MHz), Low Offset
Current Amplifier
Overvoltage and Overcurrent
protection
Two UVLO Threshold Options
150碌A(chǔ) Startup Supply Current Typical
Precision 1% 7.5V Reference
PRELIMINARY
DESCRIPTION
The UC1855A/B provides all the control features necessary for high
power, high frequency PFC boost converters. The average current mode
control method allows for stable, low distortion AC line current program-
ming without the need for slope compensation. In addition, the UC1855
utilizes an active snubbing or ZVT (Zero Voltage Transition technique) to
dramatically reduce diode recovery and MOSFET turn-on losses, result-
ing in lower EMI emissions and higher efficiency. Boost converter
switching frequencies up to 500kHz are now realizable, requiring only an
additional small MOSFET, diode, and inductor to resonantly soft switch
the boost diode and switch. Average current sensing can be employed
using a simple resistive shunt or a current sense transformer. Using the
current sense transformer method, the internal current synthesizer circuit
buffers the inductor current during the switch on-time, and reconstructs
the inductor current during the switch off-time. Improved signal to noise
ratio and negligible current sensing losses make this an attractive solution
for higher power applications.
The UC1855A/B also features a single quadrant multiplier, squarer, and
divider circuit which provides the programming signal for the current
loop. The internal multiplier current limit reduces output power during low
line conditions. An overvoltage protection circuit disables both controller
outputs in the event of a boost output OV condition.
Low startup supply current, UVLO with hysteresis, a 1% 7.5V reference,
voltage amplifier with softstart, input supply voltage clamp, enable com-
parator, and overcurrent comparator complete the list of features. Avail-
able packages include: 20 pin N, DW, Q, J, and L.
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BLOCK DIAGRAM
UDG-94001-2
License Patent from Pioneer Magnetics. Pin numbers refer to DIL-20 J or N packages.
4/97
UC3855BN 產(chǎn)品屬性
20
集成電路 (IC)
PMIC - PFC（功率因數(shù)修正）
-
平均電流
500kHz
150µA
10.5 V ~ 20 V
0°C ~ 70°C
通孔
20-DIP（0.300"，7.62mm）
20-PDIP
管件
296-11315-5
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