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參數(shù)資料
| 型號： | ML4804CP |
| 廠商： | FAIRCHILD SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Power Factor Correction and PWM Controller Combo |
| 中文描述： | 1 A POWER FACTOR CONTROLLER WITH POST REGULATOR, 250 kHz SWITCHING FREQ-MAX, PDIP16 |
| 封裝： | PLASTIC, DIP-16 |
| 文件頁數(shù)： | 9/14頁 |
| 文件大?。?/td> | 145K |
| 代理商： | ML4804CP |
ML4804
REV. 1.0.2 3/9/2001
9
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
shut down. The PWM section will continue to operate. The
OVP comparator has 250mV of hysteresis, and the PFC
will not restart until the voltage at V
FB
drops below 2.50V.
The V
FB
should be set at a level where the active and
passive external power components and the ML4804 are
within their safe operating voltages, but not so low as to
interfere with the boost voltage regulation loop.
V
CC
OVP
The V
CC
OVP feature of the ML4804 works along with the
TriFault
TM
Detect as a redundant PFC buss voltage limiter,
to prevent a damaged and broken connection or
component from causing an unsafe fault condition.
V
CC
OVP assumes that V
CC
is generated from a bootstrap
winding on the PFC boost inductor, or by some other
means whereby V
CC
is proportional to V
BUSS
. If the
proportionality is exact, then a nominal V
BUSS
of 385V at
V
CC
= 15.0V will cause the V
CC
OVP comparator to shut
the PFC down when V
BUSS
= [(16.4/15.0) x 385V] = 444V.
The PFC will then remain in the shutdown state until V
CC
declines to 13.0V, at which time the PFC will restart. If
the PFC V
CC
again encounters an over voltage condition,
the protection cycle will repeat. Note that the PWM stage
of the ML4804 remains operational even when the PFC
goes into V
CC
OVP shutdown.
For a real-world example, assume that the bootstrap
supply is derived from a conventional boost inductor
winding and rectified using Shottky diodes. Then it follows
that the voltage from the bootstrap winding must equal
15.8V during regular circuit operation, and will increase
to 17.2V at the point of V
CC
OVP shutdown. Then the
output voltage from the PFC will have increased from a
noninal V
BUSS
of 385VDC to (17.2/15.8) x 385V =
419VDC. When V
BUSS
reaches 419V, the PFC will shut
off, thereby protecting the output (BUSS) capacitor and
the semiconductors in both the PFC and PWM stages.
To assure reasonable headroom in which to operate this
device, V
CC
OVP tracks with UVLO. The V
CC
OVP
threshold is always at least 2V above that of the UVLO.
To assure reliable operation of the ML4804, V
CC
must be
operated from a bootstrap winding on the PFC
’
s inductor,
or from an external power supply whose output is
regulated to 15.0V (nominal). In the case of a regulated
power supply powering the ML4804, the V
CC
OVP function
will be rendered non-operational.
Error Amplifier Compensation
The PWM loading of the PFC can be modeled as a
negative resistor; an increase in input voltage to the PWM
causes a decrease in the input current. This response
dictates the proper compensation of the PFC's two
transconductance error amplifiers. Figure 2 shows the
types of compensation networks most commonly used for
the voltage and current error amplifiers, along with their
respective return points. The current loop compensation is
returned to V
REF
to produce a soft-start characteristic on
the PFC: as the reference voltage comes up from zero
volts, it creates a differentiated voltage on IEAO which
prevents the PFC from immediately demanding a full duty
cycle on its boost converter.
There are two major concerns when compensating the
Figure 2. Compensation Network Connections for the
Voltage and Current Error Amplifiers
Figure 3. External Component Connections to V
CC
FUNCTIONAL DESCRIPTION
(Continued)
15
VEAO
IEAO
VFB
IAC
VRMS
ISENSE
2.5V
–
+
16
2
4
3
VEA
+
–
IEA
+
–
VREF
1
PFC
OUTPUT
GAIN
MODULATOR
ML4804
VCC
GND
VBIAS
0.22μF
CERAMIC
15V
ZENER
RBIAS
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| ML4804CS | Power Factor Correction and PWM Controller Combo |
| ML4804IP | Power Factor Correction and PWM Controller Combo |
| ML4804IS | Power Factor Correction and PWM Controller Combo |
| ML4804 | Power Factor Correction and PWM Controller Combo(功率因數(shù)校正器和PWM控制器組合芯片) |
| ML4805 | Variable Feedforward PFC/PWM Controller Combo |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ML4804CS | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:Power Factor Correction and PWM Controller Combo |
| ML4804IP | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:Power Factor Correction and PWM Controller Combo |
| ML4804IS | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:Power Factor Correction and PWM Controller Combo |
| ML4805 | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:Variable Feedforward PFC/PWM Controller Combo |
| ML4805CP | 功能描述:功率因數(shù)校正 IC DIP-18 RoHS:否 制造商:Fairchild Semiconductor 開關(guān)頻率:300 KHz 最大功率耗散: 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Reel |
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