IR1153S
www.irf.com
8
?2011 International Rectifier
IR1153 General Description
The 糚FC IR1153 IC is intended for power factor
correction in continuous conduction mode Boost PFC
converters operating at fixed switching frequency with
average current mode control. The IC operates based
on IR's proprietary "One Cycle Control" (OCC) PFC
algorithm   based   on   the   concept   of   resettable
integrator.
Theory of Operation
The OCC algorithm based on the resettable integrator
concept works using two loops - a slow outer voltage
loop and a fast inner current loop. The outer voltage
loop monitors the VFB pin and generates an error
signal which controls the amplitude of the input current
admitted into the PFC converter. In this way, the outer
voltage loop maintains output voltage regulation. The
voltage loop bandwidth is kept low enough to not track
the 2xf
AC
ripple in the output voltage and thus
generates an almost DC error signal under steady
state conditions.
The inner current loop maintains the sinusoidal profile
of the input current and thus is responsible for power
factor correction. The information about the sinusoidal
variation in input voltage is inherently available in the
input line current (or boost inductor current). Thus
there is no need to sense the input voltage to
generate   a   current   reference.   The   current   loop
employs the boost inductor current information to
generate PWM signals with a proportional sinusoidal
variation. This controls the shape of the input current
to be proportional to and in phase with the input
voltage. Average current mode operation is envisaged
by filtering the switching frequency ripple from the
current sense signal using an appropriately sized on-
chip RC filter. This filter also contributes to the
bandwidth of the current control loop. Thus the filter
bandwidth has to be high enough to track the 120Hz
rectified, sinusoidal current waveform and also filter
out the switching frequency ripple in the inductor
current.   In   IR1153   this   averaging   function   can
effectively filter high ripple current ratios (as high as
40% at maximum input current) to accommodate
designs with small boost inductances.
The IC determines the boost converter instantaneous
duty cycle based on the resettable integrator concept.
The required signals are the voltage feedback loop
error signal V
m
(which is the V
COMP
pin voltage minus a
DC offset of V
COMP,START
) and the current sense signal
V
ISNS
. The resettable integrator generates a cycle-by-
cycle, saw-tooth signal called the PWM Ramp which
has an amplitude V
m
and period 1/f
SW
hence a slope of
V
m*
f
SW
.
The current sense signal is amplified by the current
amplifier by a factor g
DC
and fed into the summing
node where it is subtracted from V
m
to generate the
summer voltage (= V
m
g
DC
*V
ISNS
). The summer
voltage is compared with the PWM ramp by the
PWM comparator of the IC to determine the gate
drive   duty   cycle.   The   instantaneous   duty   is
mathematically given by:
D = (V
m
- g
DC
.V
ISNS
)/V
m
Assuming steady state condition where the voltage
feedback loop is well regulated (V
m
& V
OUT
are DC
signals) & hence instantaneous duty cycle follows
the boost-converter equation (D = 1 V
IN
(t)/V
OUT
),
the control equation can be re-written as:
V
m
= g
DC
.V
ISNS
/(V
IN
(t)/V
OUT
)
Further, recognizing that V
ISNS
= I
L
(t).R
SNS
and re-
arranging yields:
g
DC
.I
L
(t).R
SNS
= V
m
V
IN
(t)/V
OUT
Since V
m
, V
OUT
& g
DC
are constant terms:
I
L
(t) ?V
IN
(t)
Thus the inductor current follows the input voltage
waveform & by definition power factor correction is
achieved.
Feature set
Fixed Frequency Operation
The IC is programmed to operate at a fixed
frequency of 22.2kHz (Typ). Internalization of the
oscillator offers excellent noise immunity even in
the noisy PFC environment while integration of the
oscillator into the OCC core of the IC eliminates
need for digital calibration circuits. Both these
factors render the gate drive jitter free thus
contributing to elimination of audible noise in PFC
magnetics.
IC Supply Circuit & Low start-up current
The IR1153 UVLO circuit maintains the IC in UVLO
mode during start-up if VCC pin voltage is less than
the VCC turn-on threshold, V
CC,ON
and current
consumption is less than 75uA. Should VCC pin
voltage should drop below V
CC,UVLO
during normal
operation, the IC is pushed back into UVLO mode
and VCC pin has to exceed V
CC,ON
again for normal
operation. There is no internal voltage clamping of
the VCC pin.
User initiated Micropower Sleep mode
The IC can be actively pushed into a micropower
Sleep Mode where current consumption is less
than 75uA by pulling OVP/EN pin below the Sleep
threshold, V
SLEEP
even while VCC is above V
CC,ON
.
This allows the user to disable PFC during
application stand-by situations in order to meet
stand-by regulations. Since V
SLEEP
is less than 1V,
even logic level signals can be employed.