May 1999
PRELIMINARY
ML4804
Power Factor Correction and PWM Controller Combo
GENERAL DESCRIPTION
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.
FEATURES
s
Internally synchronized leading-edge modulated PFC
and trailing-edge modulated PWM in one IC
TriFault Detect
TM
for UL1950 compliance and
enhanced safety
V
CC
OVP provides additonal PFC fault protection
Slew rate enhanced transconductance error amplifier
for ultra-fast PFC response
Low power: 200µA startup current, 5.5mA operating
current
Low total harmonic distortion, high PF
Reduces ripple current in the storage capacitor
between the PFC and PWM sections
Average current, continuous boost leading edge PFC
PWM configurable for current-mode or voltage mode
operation
Overvoltage and brown-out protection, UVLO, and soft
start
s
s
s
s
s
s
s
s
s
BLOCK DIAGRAM
16
VEAO
VFB
15
2.5V
IAC
2
VRMS
4
ISENSE
3
RAMP 1
7
RAMP 2
8
OSCILLATOR
DUTY CYCLE
LIMIT
-
+
-
-
+
-
1
IEAO
POWER FACTOR CORRECTOR
TRI-FAULT
+
–
13
OVP
+
2.75V
VCCOVP
VCC
16.4V
+
+
–
-
VCC
17V
VCC
7.5V
REFERENCE
Q
Q
PFC OUT
Q
Q
12
VREF
14
VEA
1.6kΩ
+
IEA
0.5V
S
-1V
+
-
GAIN
MODULATOR
1.6kΩ
R
S
R
-
PFC ILIMIT
VDC
6
VCC
SS
5
25µA
1.25V
S
VFB
2.45V
-
+
Q
Q
PWM OUT
11
VIN OK
1.0V
-
+
+
R
DC ILIMIT
DC ILIMIT
9
VREF
PULSE WIDTH MODULATOR
VCC
UVLO
1
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
