ML4804 Datasheet, PDF (1/14 Pages) Fairchild Semiconductor – Power Factor Correction and PWM Controller Combo

May 1999
PRELIMINARY
ML4804
Power Factor Correction and PWM Controller Combo
GENERAL DESCRIPTION
FEATURES
The ML4804 is a controller for power factor corrected,
switched mode power supplies. Power Factor Correction
(PFC) allows the use of smaller, lower cost bulk
capacitors, reduces power line loading and stress on the
switching FETs, and results in a power supply that fully
complies with IEC1000-3-2 specification. Intended as a
BiCMOS enhancement of the industry-standard ML4824,
the ML4804 includes circuits for the implementation of
leading edge, average current, “boost” type power factor
correction and a trailing edge, pulse width modulator
(PWM). It also includes a TriFault Detect™ function to
help ensure that no unsafe conditions will result from
single component failure in the PFC. 1A gate-drive
outputs minimize the need for external driver circuits.
Low power requirements improve efficiency and reduce
component costs.
An over voltage comparator shuts down the PFC section
in the event of a sudden decrease in load. The PFC
section also includes peak current limiting and input
voltage brownout protection. The PWM section can be
operated in current or voltage mode, at up to 250kHz,
and includes an accurate 50% duty cycle limit to prevent
transformer saturation.
s Internally synchronized leading-edge modulated PFC
and trailing-edge modulated PWM in one IC
s TriFault Detect^TM for UL1950 compliance and
enhanced safety
s V_CCOVP provides additonal PFC fault protection
s Slew rate enhanced transconductance error amplifier
for ultra-fast PFC response
s Low power: 200µA startup current, 5.5mA operating
current
s Low total harmonic distortion, high PF
s Reduces ripple current in the storage capacitor
between the PFC and PWM sections
s Average current, continuous boost leading edge PFC
s PWM configurable for current-mode or voltage mode
operation
s Overvoltage and brown-out protection, UVLO, and soft
start
BLOCK DIAGRAM
16
VEAO
1
IEAO
VFB
15
2.5V
IAC
2
VRMS
4
ISENSE
3
VEA
-
+
1.6kΩ ^IEA
+
-
GAIN
MODULATOR
1.6kΩ
POWER FACTOR CORRECTOR
0.5V
TRI-FAULT
+
–
VCC
VCCOVP
+
16.4V ^–
+
2.75V
-1V
OVP
+
-
+
-
-
PFC ILIMIT
RAMP 1
7
OSCILLATOR
RAMP 2
8
DUTY CYCLE
LIMIT
VCC
17V
13
VCC
7.5V
REFERENCE
VREF
14
SQ
RQ
SQ
PFC OUT
12
RQ
VDC
6
VCC
SS
5
25µA
1.25V
DC ILIMIT VREF
9
-
+
-
+
VFB
2.45V
VIN OK
-
+
1.0V
-
+
DC ILIMIT
PULSE WIDTH MODULATOR
VCC
SQ
RQ
PWM OUT
11
UVLO
1