MC33262 データシートの表示（PDF） - Motorola => Freescale
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MC33262 Datasheet PDF : 16 Pages
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MC34262 MC33262
FUNCTIONAL DESCRIPTION
Introduction
With the goal of exceeding the requirements of legislation
on line–current 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,
cost–effective 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 15.
Figure 15. Uncorrected Power Factor Circuit
Rectifiers
Converter
AC
Line
+
Bulk
Storage
Load
Capacitor
can be made to appear resistive to the ac line, thus
significantly reducing the harmonic current content.
Figure 16. Uncorrected Power Factor
Input Waveforms
Vpk
Rectified
DC
0
Line Sag
AC Line
Voltage
0
AC Line
Current
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 16. 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 17. 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
The MC34262, MC33262 are high performance, critical
conduction, current–mode power factor controllers
specifically designed for use in off–line 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.
Operating Description
The MC34262, MC33262 contain many of the building
blocks and protection features that are employed in modern
high performance current mode power supply controllers.
There are, however, two areas where there is a major
difference when compared to popular devices such as the
UC3842 series. Referring to the block diagram in Figure 19,
note that a multiplier has been added to the current sense
loop and that this device does not contain an oscillator. The
reasons for these differences will become apparent in the
following discussion. A description of each of the functional
blocks is given below.
Figure 17. Active Power Factor Correction Preconverter
Rectifiers
PFC Preconverter
Converter
AC
Line
High
+ Frequency
Bypass
Capacitor
MC34362
+
Bulk
Storage
Capacitor
Load
6
MOTOROLA ANALOG IC DEVICE DATA
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