Features

Control Boost-PWM near the unit power factor

Limit line current inflammation is less than 3%

global No switch operation

Accurate power limit

fixed frequency average current mode control

high bandwidth (5MHz), low partial partial partial partial partial partial partial partial partial partial partial Electric -migrant exile

Integrated current and voltage amplifier output card hoop

multiplier improvement: linear, 500 MV VAC offset (eliminating external resistance), 0 V V To 5V multi -mode range

VREF good comparator

faster and higher accuracy make the comparator

UVLO Options (16 volts/10 volts or 10.5 volts/10 volts)

300-a startup power current

Block figure

Explanation

UC3854A

/B product is a compatible enhanced version of UC3854. Like UC3854, these products provide all the functions required for the pre -adjusted by the active power factor correction. The controller plastic surgery through the current waveform of the AC input cable, which corresponds to the AC input cable voltage, thereby achieving the purpose of approaching the power factor of the unit. To this end, UC3854A/B uses the average current mode control. Different from the peak current mode control, the average current mode control maintains stable and low -distorted sine line current without the need for slopes.

A 1%, 7.5 volt voltage, fixed frequency oscillator, pulse width modulation, soft start voltage amplifier, line voltage feed (VRMS square), input power supply voltage clamp, over -current comparison rounder round Features.

Explanation (continued)

UC3854A/B product through providing broadband width, low offset current exile, faster response and higher accuracy comparison, VREF good comparator, UVLO threshold options option (Side is 16 V/10 V, which is 10.5 V/10 V from the auxiliary 12 V register when it starts.) UC3854 is improved, and the enhanced multiplication/removal circuit is improved. New functions, such as the amplifier output clamp, the improved capacity of the improved amplifier, and the low offset vacuum needle reduces external component counting while improving performance. The co -mode input range of the multiplier output/current exile input is improved, so that the designer has greater flexibility when selecting the current sensing method. Unlike its predecessor, RSET only controls the oscillator chargingStreaming has no effect on the maximum multiplier output current. At present, the current is always limited to the maximum value of 2 × IAC, which simplifies the design process and provides folding power limit under the conditions of power off and extremely low.

Functional description

The design and industrial standards of UC3854A and UC3854B series products UC3854 The pins of the positive power factor circuit are upgraded. Circuit enhancement allows users to eliminate several external components required to successfully apply UC3854 in most cases. In addition, the linear improvement of the multiplication, square and removal circuit optimizes the overall system performance. The detailed description of the circuit enhancement is as follows. For reference data on in -depth design applications, please refer to the application description, UC3854 control power factor Correct circuit design (SLUA144), UC3854A, and UC3854B advanced power factor correction control IC (SLUA177).

multiplication/square and division

This is basically the same as UC3854, but the difference in circuit has improved performance and application.

The first difference is IAC input. Throughout the working temperature range, UC3854A/B adjusted the pins voltage to the nominal 500 MV instead of 6.0 V used on UC3854. The low offset voltage eliminates the needs of the UC3854 design requirements from IAC to VREF. In order to obtain the best performance, the maximum current of the high -voltage line connected to the IAC should be limited to 250 Weire.

Use UC3854A/B to improve the linear working range of the VRMS foot. The input range of VRMS expands from 0V to 5.5V. Because the UC3854A square circuit uses an analog multiplier, not linear approximation, it improves accuracy and eliminates discontinuousness. The external pressure device network connected to the VRMS should generate 1.5 volt voltage under the low voltage line (85 volt communication). This makes the voltage of VRMS on high -voltage lines (270 volt aggregation) 4.77 volt, which is within its working scope.

The voltage amplifier output constitutes the third input of the multiplier, and the internal restraint is 6.0V. This eliminates the outer Zina uncommon in the UC3854 design. On UC3854A/B, the offset voltage of the multiplier input end increased to 1.5 V.

The output tube of the multiplier is also a common pipe foot for non-inverse input of current discharge. Compared with the -0.3 V to 2.5 V of UC3854, its output range is -0.3 V to 5.0 V. This improvement makes UC3854A/B in applications with a very large range of current detection signals.

Voltage amplifier

The design of UC3854A/B voltage amplifier is basically similar to UC3854, but there are twoexception. The first is internal connection. The lower voltage reduces the amount of charge on the compensation capacitor, thereby improving the recovery from a large signal event (such as line interrupt or power interruption). It also minimizes the DC current through feedback. The output of the voltage amplifier has also changed. In addition to a 6.0 volt temperature compensation clamp, the output short -circuit current has been reduced to 2 mAh. A proactive drop -down has replaced the passive pull down of UC3854.

current exile large device

The current sealing of the current PFC controller requires a lower bias voltage to minimize the circulation of the line current. In view of this, the UC3854A/B current exiles increase the input bias voltage from ± 4mv to 0V, to ± 3mv. The negative displacement of UC3854A/B guarantees that when the current instruction is zero (the current input is zero), the PWM circuit will not drive MOSFET. The previous design required external offset offset the network to achieve this key feature. The bandwidth of the current exile has increased to 5MHz. Although this is usually not the problem of 50 Hz or 60 Hzhz, this is essential for the application of 400 Hzhz input aviation electronic equipment.

Other

UC3854A/B also implemented other important enhancement functions. 20 V's AVCC power supply voltage clamping allows the controller to feed current when required. The lower start -up power current (typical value is 250 Wei'an) greatly reduces the power requirements of the offline starting resistor. 10.5 V/10 V UVLO options (UC3854B) enable the controller to turn off the auxiliary 12 V power supply.

VREF good comparator ensures that if the power supply of the 7.5V reference voltage has not yet started, the MOSFET drive output is still very low. This improvement eliminates the needs of the multi -way output tube foot required for the outer Schottky diode on PKLMT and some UC3854 design. The dissemination of disabled characteristics has been increased to typical 300ns. This delay is directly proportional to the size of the VREF capacitor on the UC3854, and it is usually a number of levels of magnitude slower.