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參數(shù)資料
| 型號： | FAN4800 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Low Start-Up Current PFC/PWM Controller Combos |
| 中文描述： | 低啟動電流式PFC / PWM控制器功放音箱 |
| 文件頁數(shù)： | 10/19頁 |
| 文件大?。?/td> | 369K |
| 代理商： | FAN4800 |
FAN4800
10
3. The output of the voltage error amplifier, VEAO. The
gain modulator responds linearly to variations in this
voltage.
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 instanta-
neous current draw of the PFC from the power line.
The general form of the output of the gain modulator is:
More precisely, 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 around 228.47
μ
A and the maximum output
voltage of the gain modulator is limited to 228.47
μ
A*
3.5K = 0.8V.
This 0.8V will also
determine the maximum input
power. However, I
GAINMOD
cannot be measured
directly from I
SENSE
. I
SENSE
=
I
GAINMOD
-
I
OFFSET
and
I
OFFSET
can only be measured when VEAO is less than
0.5V and I
GAINMOD
is 0A. Typical I
OFFSET
is around
60
μ
A.
Selecting R
AC
for IAC pin
I
AC
pin is the input of the gain modulator. I
AC
is also a
current mirror input and it requires current input. Select-
ing a proper resistor R
AC
, will provide a good sine wave
current derived from the line voltage and also help pro-
gram the maximum input power and minimum input line
voltage.
R
AC
=V
in peak
* 7.9K. For example, if the minimum line
voltage is 80VAC, the R
AC
=80*1.414*7.9K=894Kohm.
Current Error Amplifier, IEAO
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 de-
rived from a current sense resistor in series with the
negative terminal of the input bridge rectifier.
As stated above, the inverting input of the current error
amplifier is a virtual ground. Given this fact, and the ar-
rangement of the duty cycle modulator polarities inter-
nal 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 and Selecting Rs
As well as being a part of the current feedback loop, the
I
SENSE
pin is a direct input to the cycle-by-cycle current
limiter for the PFC section. If the input voltage at this pin
is ever less than -1V, the output of the PFC will be dis-
abled until the protection flip-flop is reset by the clock
pulse at the start of the next PFC power cycle.
Rs is the sensing resistor of the PFC boost converter.
During the steady state, line input current*Rs equals
I
GAINMOD
*3.5K.
Since the maximum output voltage of the gain modula-
tor is I
GAINMOD
max*3.5K=0.8V during the steady state,
Rs*line input current will be limited to below 0.8V as
well. Therefore, to choose Rs, we use the following
equation:
For example, if the minimum input voltage is 80VAC,
and the maximum input RMS power is 200Watt,
R
S
= (0.8V * 80V * 1.414)/(2*200)=0.226ohm.
PFC OVP
In the FAN4800, the PFC OVP comparator serves to
protect the power circuit from being subjected to
excessive voltages if the load changes suddenly. A
resistor divider from the high voltage DC output of the
PFC is fed to V
FB
. When the voltage on V
FB
exceeds
2.78V, the PFC output driver is shut down. The PWM
section will continue to operate. The OVP comparator
has 280mV of hysteresis, and the PFC will not restart
until the voltage at V
FB
drops below 2.50V. Also, Vcc
OVP can serve
as a redundant PFC OVP protection.
VCC OVP and threshold is 17.9V with 1.5V hysteresis.
IGAINMOD
----------------------------------
VEAO
×
1V
×
=
IGAINMOD
K
=
VEAO
0.625
–
(
)
×
IAC
×
RS
0.8V
VINPEAK
(
)
2
Line Input Power
×
(
)
×
=
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| FAN4800_06 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Low Start-Up Current PFC/PWM Controller Combos |
| FAN4800_10 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Low Startup Current PFC/PWM Controller Combinations |
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| FAN48002S | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:PFC/PWM Controller Combination |
| FAN4800A | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:PFC/PWM Controller Combination |
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