PFS7323-7329
DRAIN (D)
BOOST DIODE CATHODE (K)
VOLTAGE MONITOR (V)
I
V
INPUT
LINE INTERFACE
Peak
Detector
Input UV
(I
UV+
/I
UV-
)
I
VPK
M
ON
FB
OV
M
OFF
(I
REF
- I
V
)
~(V
O-
V
IN
)
C
INT
I
V
I
REF
INTERNAL
SUPPLY
SOFT-
START
BIAS POWER (VCC)
+
-
V
CC+
C
UV
/
FB
OFF
/
VREF
FBC
OV
C
OFF
I
OCP
V
PG(H)
I
PGT
FBC
UV
REFERENCE
(R)
REFERENCE
AND BAND GAP
Feedback-OVP/OFF
Comparator
FEEDBACK/
COMPENSATION Pin
OV/UV
TIMER
SUPERVISOR
Power
MOSFET
senseFET
VCC
Latch
V
OFF
is a function of the error-voltage
(V
E
) and is used to reduce the
average operating frequency as a
function of output power
V
OFF
+
-
FB
ON
/
FB
OFF
V
FB
FEEDBACK
(FB)
V
CC
+
Comparator
-
+
V
OFF
V
E
Frequency
Slide
V
E
+
-
I
S
Transconductance
Error-Ampli er
Internal
1 kHz Filter
Reference
V
REF
+
-
I
VPK
FB
GM
-
FBC
OV
+
-
+
-
Buffer and
De-Glitch Filter
+
LEB
FB
GM
-
FBC
UV
COMPENSATION
(C)
Comparator
I
OCP
+
-
OCP
m
ON
is the switch
current sense scale
factor which is a function
of the peak input voltage
C
INT
P
ON
×
M
ON
×
I
S
INPUT UV
OTP SOA
C-UV/OFF
Comparator
+
C
UV
/C
OFF
V
FB
V
CC
V
PG(H)
I
PGT
POWER GOOD
THRESHOLD
(PGT)
+
POWER GOOD
(PG)
SOURCE (S)
GROUND (G)
PI-6697-050312
Figure 3.
Functional Block Diagram.
Functional Description
The HiperPFS-2 is a variable switching frequency boost PFC
solution. More specifically, it employs a constant amp-second
on-time and constant volt-second off-time control algorithm.
This algorithm is used to regulate the output voltage and shape
the input current to comply with regulatory harmonic current
limits (high power factor). Integrating the switch current and
controlling it to have a constant amp-sec product over the
on-time of the switch allows the average input current to follow
the input voltage. Integrating the difference between the output
and input voltage maintains a constant volt-second balance
dictated by the electro-magnetic properties of the boost
inductor and thus regulates the output voltage and power.
More specifically, the control technique sets constant volt-
seconds for the off-time (t
OFF
). The off-time is controlled such
that:
^
V
O
-
V
IN
h
#
t
OFF
=
K
1
(1)
Since the volt-seconds during the on-time must equal the
volt-seconds during the off-time, to maintain flux equilibrium in
the PFC choke, the on-time (t
ON
) is controlled such that:
V
IN
#
t
ON
=
K
1
(2)
The controller also sets a constant value of charge during each
on-cycle of the power MOSFET. The charge per cycle is varied
gradually over many switching cycles in response to load
changes so it can be regarded as substantially constant for a
half line cycle. With this constant charge (or amp-second)
control, the following relationship is therefore also true:
I
IN
#
t
ON
=
K
2
Substituting t
ON
from (2) into (3) gives:
(3)
I
IN
=
V
IN
#
K
2
K
1
(4)
4
Rev. B 06/13
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