MC33262DG【PDF 6/19 页】IC PFC CONTROLLER CRM 8SOIC

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Sheet目录44

2页 3页 4页 5页 [6页]7页 8页 9页 10页

MC34262, MC33262

http://onsemi.com

, SUPPLY VOLTAGE (V)

= 0 V

Current Sense = 0 V

Multiplier = 0 V

= 1.0 nF

f = 50 kHz

= 25癈

-55

-25

100

125

, AMBIENT TEMPERATURE (癈)

Figure 14. Supply Current

versus Supply Voltage

Figure 15. Undervoltage Lockout Thresholds

versus Temperature

Startup Threshold

Increasing)

8.0

4.0

9.0

7.0

8.0

Minimum Operating Threshold

Decreasing)

FUNCTIONAL DESCRIPTION

Introduction

With the goal of exceeding the requirements of

legislation on linecurrent harmonic content, there is an

ever increasing demand for an economical method of

obtaining a unity power factor. This data sheet describes a

monolithic control IC that was specifically designed for

power factor control with minimal external components. It

offers the designer a simple, costeffective solution to

obtain the benefits of active power factor correction.

Most electronic ballasts and switching power supplies

use a bridge rectifier and a bulk storage capacitor to derive

raw dc voltage from the utility ac line, Figure 16.

Figure 16. Uncorrected Power Factor Circuit

Line

Rectifiers

Converter

Bulk

Storage

Capacitor

Load

This simple rectifying circuit draws power from the line

when the instantaneous ac voltage exceeds the capacitor

voltage. This occurs near the line voltage peak and results

in a high charge current spike, Figure 17. Since power is

only taken near the line voltage peaks, the resulting spikes

of current are extremely nonsinusoidal with a high content

of harmonics. This results in a poor power factor condition

where the apparent input power is much higher than the real

power. Power factor ratios of 0.5 to 0.7 are common.

Power factor correction can be achieved with the use of

either a passive or an active input circuit. Passive circuits

usually contain a combination of large capacitors,

inductors, and rectifiers that operate at the ac line

frequency. Active circuits incorporate some form of a high

frequency switching converter for the power processing,

with the boost converter being the most popular topology,

Figure 18. Since active input circuits operate at a frequency

much higher than that of the ac line, they are smaller,

lighter in weight, and more efficient than a passive circuit

that yields similar results. With proper control of the

preconverter, almost any complex load can be made to

appear resistive to the ac line, thus significantly reducing

the harmonic current content.

Figure 17. Uncorrected Power Factor

Input Waveforms

Rectified

AC Line

Voltage

AC Line

Current

Line Sag

The MC34262, MC33262 are high performance, critical

conduction, currentmode power factor controllers

specifically designed for use in offline active

preconverters. These devices provide the necessary

features required to significantly enhance poor power

factor loads by keeping the ac line current sinusoidal and

in phase with the line voltage.

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