參數(shù)資料
型號: ML4800
廠商: Fairchild Semiconductor Corporation
元件分類: 基準電壓源/電流源
英文描述: Power Factor Correction and PWM Controller Combo(功率因數(shù)校正器和PWM控制器組合芯片)
中文描述: 功率因數(shù)校正和PWM控制器組合(功率因數(shù)校正器和脈寬調制控制器組合芯片)
文件頁數(shù): 8/14頁
文件大?。?/td> 270K
代理商: ML4800
ML4800
8
REV. 1.0 10/10/2000
The output of the gain modulator is a current signal, in the
form of a full wave rectified sinusoid at twice the line
frequency. This current is applied to the virtual-ground
(negative) input of the current error amplifier. In this way
the gain modulator forms the reference for the current
error loop, and ultimately controls the instantaneous
current draw of the PFC from the power line. The general
form for the output of the gain modulator is:
More exactly, the output current of the gain modulator is
given by:
where K is in units of V
-1
.
Note that the output current of the gain modulator is
limited to 500
μ
A.
Current Error Amplifier
The current error amplifier
s output controls the PFC duty
cycle to keep the average current through the boost
inductor a linear function of the line voltage. At the
inverting input to the current error amplifier, the output
current of the gain modulator is summed with a current
which results from a negative voltage being impressed
upon the I
SENSE
pin. The negative voltage on I
SENSE
represents the sum of all currents flowing in the PFC
circuit, and is typically derived from a current sense
resistor in series with the negative terminal of the input
bridge rectifier. In higher power applications, two current
transformers are sometimes used, one to monitor the I
D
of
the boost MOSFET(s) and one to monitor the I
F
of the
boost diode. As stated above, the inverting input of the
current error amplifier is a virtual ground. Given this fact,
and the arrangement of the duty cycle modulator polarities
internal to the PFC, an increase in positive current from
the gain modulator will cause the output stage to increase
its duty cycle until the voltage on I
SENSE
is adequately
negative to cancel this increased current. Similarly, if the
gain modulator
s output decreases, the output duty cycle
will decrease, to achieve a less negative voltage on the
I
SENSE
pin.
Cycle-By-Cycle Current Limiter
The I
SENSE
pin, as well as being a part of the current
feedback loop, is a direct input to the cycle-by-cycle
current limiter for the PFC section. Should the input
voltage at this pin ever be more negative than -1V, the
output of the PFC will be disabled until the protection flip-
flop is reset by the clock pulse at the start of the next PFC
power cycle.
TriFault Detect
TM
To improve power supply reliability, reduce system
component count, and simplify compliance to UL 1950
safety standards, the ML4800 includes TriFault Detect. This
feature monitors VFB (Pin 15) for certain PFC fault
conditions.
In the case of a feedback path failure, the output of the
PFC could go out of safe operating limits. With such a
failure, VFB will go outside of its normal operating area.
Should VFB go too low, too high, or open, TriFault Detect
senses the error and terminates the PFC output drive.
TriFault detect is an entirely internal circuit. It requires no
external components to serve its protective function.
Overvoltage Protection
The OVP comparator serves to protect the power circuit
from being subjected to excessive voltages if the load
should suddenly change. A resistor divider from the high
voltage DC output of the PFC is fed to V
FB
. When the
voltage on V
FB
exceeds 2.75V, the PFC output driver is
15
VEAO
IEAO
VFB
IAC
VRMS
ISENSE
RAMP 1
OSCILLATOR
OVP
+
PFC ILIMIT
TRI-FAULT
2.5V
+
16
2
4
3
VEA
7
+
IEA
1
+
+
PFC OUT
12
S
R
Q
Q
S
R
Q
Q
2.75V
1V
+
0.5V
1.6k
1.6k
GAIN
MODULATOR
Figure 1. PFC Section Block Diagram
FUNCTIONAL DESCRIPTION
(Continued)
I
I
VEAO
2
V
V
GAINMOD
AC
RMS
=
×
×
1
(1)
I
K
VEAO
V
I
GAINMOD
AC
=
×
×
(
.
)
0625
相關PDF資料
PDF描述
ML4801CP Variable Feedforward PFC/PWM Controller Combo
ML4801CS Variable Feedforward PFC/PWM Controller Combo
ML4801IP Variable Feedforward PFC/PWM Controller Combo
ML4801IS Variable Feedforward PFC/PWM Controller Combo
ML4801 Variable Feedforward PFC/PWM Controller Combo(前饋可變PFC/PWM控制器組合芯片)
相關代理商/技術參數(shù)
參數(shù)描述
ML4800_0109 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Power Factor Correction and PWM Controller Combo
ML4800CP 功能描述:功率因數(shù)校正 IC PFC Controller PWM Combo RoHS:否 制造商:Fairchild Semiconductor 開關頻率:300 KHz 最大功率耗散: 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Reel
ML4800CP 制造商:Fairchild Semiconductor Corporation 功能描述:IC PFC/PWM COMBO 4800 DIP16
ML4800CP_NL 功能描述:功率因數(shù)校正 IC Power Factor PWM Contrl 0.2mA 81KHz RoHS:否 制造商:Fairchild Semiconductor 開關頻率:300 KHz 最大功率耗散: 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Reel
ML4800CP_Q 功能描述:功率因數(shù)校正 IC PFC Controller PWM Combo RoHS:否 制造商:Fairchild Semiconductor 開關頻率:300 KHz 最大功率耗散: 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Reel