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參數(shù)資料
| 型號： | CM6504 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | 8-PIN SINGLE PFC CONTROLLER WITH 50% PWM CLOCK SIGNAL |
| 中文描述： | 8針單PFC控制器的50％PWM時鐘信號 |
| 文件頁數(shù)： | 7/13頁 |
| 文件大?。?/td> | 182K |
| 代理商： | CM6504 |
CM6503/4
8-PIN S
INGLE
PFC C
ONTROLLER
W
ITH 50%
PWM
C
LOCK
S
IGNAL
possible to the IC. Good bypassing is critical to the proper
operation of the CM6503/4.
VCC is typically produced by an additional winding off the
boost inductor or PFC Choke, providing a voltage that is
proportional to the PFC output voltage. Since the VCC OVP
max voltage is 19.4V, an internal shunt limits VCC
overvoltage to an acceptable value. An external clamp,
such as shown in Figure 1, is desirable but not necessary.
VCC
2002/07/16
Preliminary
Rev. 0.2
Champion Microelectronic Corporation
Page 7
GND
1N5250B
Figure 1. Optional VCC Clamp
This limits the maximum VCC that can be applied to the IC
while allowing a VCC which is high enough to trip the VCC
OVP. An RC filter at VCC is required between boost trap
winding and VCC.
PWMCLK (Pin 8)
PWMCLK is the PWM Clock signal for the down stream DC
to DC PWM stage. This signal will not be on until the PFC
boost output reaches steady state which means VFB has
reaches 2.45V. (Typical PFC boost output is around 380V.
Then PWMCLK will send out 50% clock signal which has
been perfectly aligned with PFCOUT signal which is leading
edge modulation.
Power Factor Correction
Power factor correction makes a nonlinear load look like a
resistive load to the AC line. For a resistor, the current
drawn from the line is in phase with and proportional to the
line voltage, so the power factor is unity (one). A common
class of nonlinear load is the input of most power supplies,
which use a bridge rectifier and capacitive input filter fed
from the line. The peak-charging effect, which occurs on
the input filter capacitor in these supplies, causes brief
high-amplitude pulses of current to flow from the power line,
rather than a sinusoidal current in phase with the line
voltage. Such supplies present a power factor to the line of
less than one (i.e. they cause significant current harmonics
of the power line frequency to appear at their input). If the
input current drawn by such a supply (or any other
nonlinear load) can be made to follow the input voltage in
instantaneous amplitude, it will appear resistive to the AC
line and a unity power factor will be achieved.
To hold the input current draw of a device drawing power
from the AC line in phase with and proportional to the input
voltage, a way must be found to prevent that device from
loading the line except in proportion to the instantaneous line
voltage. The PFC section of the CM6503/4 uses a
boost-mode DC-DC converter to accomplish this. The input
to the converter is the full wave rectified AC line voltage. No
bulk filtering is applied following the bridge rectifier, so the
input voltage to the boost converter ranges (at twice line
frequency) from zero volts to the peak value of the AC input
and back to zero.
By forcing the boost converter to meet two simultaneous
conditions, it is possible to ensure that the current draws
from the power line matches the instantaneous line voltage.
One of these conditions is that the output voltage of the
boost converter must be set higher than the peak value of
the line voltage. A commonly used value is 385VFB, to allow
for a high line of 270VAC
rms
. The other condition is that the
current that the converter is allowed to draw from the line at
any given instant must be proportional to the line voltage.
PFC Control: Leading Edge Modulation with Input
Current Shaping Technique
(I.C.S.T.)
The only differences between the conventional PFC control
topology and I.C.S.T. is:
the current loop of the conventional control method is a close
loop method and it requires a detail understanding about the
system loop gain to design. With I.C.S.T., since the current
loop is an open loop, it is very straightforward to implement it.
The end result of the any PFC system, the power supply is
like a pure resistor at low frequency. Therefore, current is in
phase with voltage.
In the conventional control, it forces the input current to
follow the input voltage. In CM6503, the chip thinks if a boost
converter needs to behave like a low frequency resistor, what
the duty cycle should be.
The following equations is CM6503 try to achieve:
V
R
=
(1)
in
in
e
I
in
l
I
I
=
Equation 2 means: average boost inductor current equals to
input current.
I
V
I
V
×
≈
×
∴
(3)
Therefore, input instantaneous power is about to equal to the
output instantaneous power.
(2)
d
out
l
in
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