CM6800T Champion Microelectronic Corp., CM6800T Datasheet - Page 15

• Manufacturer Part Number: CM6800T
• Description: Epa/85+ Pfc+pwm Combo Controller Design For High Efficient Power Supply
• Manufacturer: Champion Microelectronic Corp.

http://www.championmicro.com.tw
Dynamic Soft PFC (patent pending)
is the main feature of CM6800T. Dynamic Soft PFC is to
improve the efficiency, to reduce power device stress, to ease
EMI, and to ease the monotonic output design while it has the
more protection such as the short circuit with power-foldback
protection. Its unique sequential control maximizes the
performance and the protections among steady state, transient
and the power on/off conditions.
PFC Section:
Gain Modulator
CM6800T. The gain modulator is the heart of the PFC, as it is
this circuit block which controls the response of the current
loop to line voltage waveform and frequency, rms line voltage,
and PFC output voltages. There are three inputs to the gain
modulator. These are:
1. A current representing the instantaneous input voltage
2. A voltage proportional to the long-term RMS AC line voltage,
3. The output of the voltage error amplifier, VEAO. The gain
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 formula of the output of
the gain modulator is:
2010/08/03
Besides all the goodies from CM6800A, Dynamic Soft PFC
Figure 1 shows a block diagram of the PFC section of the
The output of the gain modulator is a current signal, in the
(amplitude and wave-shape) to the PFC. The rectified AC
input sine wave is converted to a proportional current via a
resistor and is then fed into the gain modulator at I
Sampling current in this way minimizes ground noise, as is
required in high power switching power conversion
environments. The gain modulator responds linearly to this
current.
derived from the rectified line voltage after scaling and
filtering. This signal is presented to the gain modulator at
VRMS. The gain modulator’s output is inversely proportional
to V
illustrated in the Typical Performance Characteristics of this
page.
modulator responds linearly to variations in this voltage.
I
mul
RMS
=
2
I
. The relationship between V
AC
Rev. 1.2
( ×
VEAO
V
RMS
2
-
0.7V)
x constant
Champion Microelectronic Corporation
RMS
and gain is
(1)
AC
.
EPA/85+ PFC+PWM COMBO CONTROLLER
Where K is in units of [V
around 100
modulator is limited to 100uA x 7.75K≒0.8V. This 0.8V also
will determine the maximum input power.
I
when VEAO is less than 0.5V and I
I
IAC=20uA, Veao=6V
to design 80VAC with VRMS average voltage= 1.14V.
Selecting R
current mirror input and it requires current input. By selecting a
proper resistor R
derived from the line voltage and it also helps program the
maximum input power and minimum input line voltage.
R
voltage is 80VAC, the R
SENSE
OFFSET
CM6800T
AC
IAC pin is the input of the gain modulator. IAC also is a
Note that the output current of the gain modulator is limited
However, I
When VRMS below 1V, the PFC is shut off. Designer needs
=Vin min peak x 53.03K. For example, if the minimum line
= I
is around 25uA.
Design for High Efficient Power Supply
Gain
GAINMOD
μ
AC
GAINMOD
A and the maximum output voltage of the gain
=
for IAC pin
I
I
mul
-I
AC
(Turbo-Speed PFC+Green PWM)
SENSE
OFFSET
, it will provide a good sine wave current
= K x (VEAO – 0.7V) x I
Gain vs. VRMS (pin4)
K=Gain/(VEAO-0.7V)
cannot be measured directly from I
AC
-1
I
Gain=Imul/Iac
−
]
AC
=80 x 1.414 x 53.03K = 6 Mega ohm.
and I
I
OFFSET
OFFSET
=
can only be measured
I
I
GAINMOD
MUL
AC
AC
is 0A. Typical
15
SENSE
.