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参数资料
| 型号： | MC33261 |
| 厂商： | Motorola, Inc. |
| 元件分类： | 基准电压源/电流源 |
| 英文描述： | POWER FACTOR CONTROLLERS |
| 中文描述： | 功率因数控制器 |
| 文件页数： | 6/12页 |
| 文件大小： | 309K |
| 代理商： | MC33261 |
MC34261 MC33261
FUNCTIONAL DESCRIPTION
6
MOTOROLA ANALOG IC DEVICE DATA
Introduction
Most electronic ballasts and switching power supplies use
a bridge rectifier and a filter capacitor to derive raw dc voltage
from the utility ac line. This simple rectifying circuit draws
power from the line when the instantaneous ac voltage
exceeds the capacitor’s voltage. This occurs near the line
voltage peak and results in a high charge current spike.
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.
The MC34261, MC33261 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.
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.
Operating Description
The MC34261, MC33261 contains 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 15,
note that a multiplier has been added to the current sense
loop and that this device does not contain an oscillator. A
description of each of the functional blocks is given below.
Error Amplifier
A fully compensated Error Amplifier with access to the
inverting input and output is provided. It features a typical dc
voltage gain of 85 dB, and a unity gain bandwidth of 1.0 MHz
with 58
°
of phase margin (Figure 4). The noninverting input is
internally biased at 2.5 V
±
2.0% and is not pinned out. The
output voltage of the power factor converter is typically
divided down and monitored by the inverting input. The
maximum input bias current is –1.0
μ
A which can cause an
output voltage error that is equal to the product of the input
bias current and the value of the upper divider resistor R2.
The Error Amp Output is internally connected to the Multiplier
and is pinned out (Pin 2) for external loop compensation.
Typically, the bandwidth is set below 20 Hz, so that the Error
Amp output voltage is relatively constant over a given ac line
cycle. The output stage consists of a 500
μ
A current source
pull–up with a Darlington transistor pull–down. It is capable of
swinging from 2.1 V to 5.7 V, assuring that the Multiplier can
be driven over its entire dynamic range.
Multiplier
A single quadrant, two input multiplier is the critical
element that enables this device to control power factor. The
ac haversines are monitored at Pin 3 with respect to ground
while the Error Amp output at Pin 2 is monitored with respect
to the Voltage Feedback Input threshold. A graph of the
Multiplier transfer curve is shown in Figure 1. Note that both
inputs are extremely linear over a wide dynamic range, 0 V to
3.2 V for the Multiplier input (Pin 3), and 2.5 V to 4.0 V for the
Error Amp output (Pin 2). The Multiplier output controls the
Current Sense Comparator threshold (Pin 4) as the ac
voltage traverses sinusoidally from zero to peak line. This
has the effect of forcing the MOSFET peak current to track
the input line voltage, thus making the preconverter load
appear to be resistive.
Pin 4 Threshold
≈
0.62(VPin 2 – VFB)VPin 3
Zero Current Detector
The MC34261 operates as a critical conduction current
mode controller, whereby output switch conduction is
initiated by the Zero Current Detector and terminated when
the peak inductor current reaches the threshold level
established by the Multiplier output. The Zero Current
Detector initiates the next on–time by setting the RS Latch at
the instant the inductor current reaches zero. This critical
conduction mode of operation has two significant benefits.
First, since the MOSFET cannot turn on until the inductor
current reaches zero, the output rectifier’s reverse recovery
time becomes less critical allowing the use of an inexpensive
rectifier. Second, since there are no deadtime gaps between
cycles, the ac line current is continuous thus limiting the peak
switch to twice the average input current.
The Zero Current Detector indirectly senses the inductor
current by monitoring when the auxiliary winding voltage falls
below 1.6 V. To prevent false tripping, 110 mV of hysteresis is
provided. The Zero Current Detector input is internally
protected by two clamps. The upper 6.7 V clamp prevents
input overvoltage breakdown while the lower 0.7 V clamp
prevents substrate injection. Device destruction can result if
this input is shorted to ground. An external resistor must be
used in series with the auxiliary winding to limit the current
through the clamps.
Current Sense Comparator and RS Latch
The Current Sense Comparator RS Latch configuration
ensures that only a single pulse appears at the Drive Output
during a given cycle. The inductor current is converted to a
voltage by inserting a ground referenced sense resistor R9 in
series with the source of output switch Q1. This voltage is
monitored by the Current Sense Input and compared to the
Multiplier output voltage. The peak inductor current is
controlled by the threshold voltage of Pin 4 where:
Pin 4 Threshold
R9
Ipk =
With the component values shown in Figure 16, the
Current Sense Comparator threshold, at the peak of the
haversine varies from 1.1 V at 90 Vac to 100 mV at 268 Vac.
The Current Sense Input to Drive Output propagation delay is
typically 200 ns.
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相关代理商/技术参数 |
参数描述 |
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| MC33261P | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| MC33262 | 制造商:SPC Multicomp 功能描述:HEATSINK TO220/218 12.9/W 制造商:SPC Multicomp 功能描述:HEATSINK TO220/218 12.9C/W 制造商:SPC Multicomp 功能描述:HEAT SINK; Packages Cooled:TO-218 / TO-220; Thermal Resistance:12.9C/W; External Height - Imperial:1.5"; External Height - Metric:38.1mm; External Width - Imperial:0.654"; External Width - Metric:16.6mm; Heat Sink Material:Aluminium;RoHS Compliant: Yes |
| MC33262CDR2 | 功能描述:功率因数校正 IC ANA PFC W/OVERVOLT COMP RoHS:否 制造商:Fairchild Semiconductor 开关频率:300 KHz 最大功率耗散: 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SOIC-8 封装:Reel |
| MC33262CDR2G | 功能描述:功率因数校正 IC ANA PFC W/OVERVOLT COMP RoHS:否 制造商:Fairchild Semiconductor 开关频率:300 KHz 最大功率耗散: 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SOIC-8 封装:Reel |
| MC33262D | 功能描述:功率因数校正 IC Critical Mode PFC RoHS:否 制造商:Fairchild Semiconductor 开关频率:300 KHz 最大功率耗散: 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SOIC-8 封装:Reel |
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