ML4824CS2X Datasheet, PDF (1/15 Pages) Fairchild Semiconductor – Power Factor Correction and PWM Controller Combo

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ML4824
Power Factor Correction and PWM Controller
Combo
Features
• Internally synchronized PFC and PWM in one IC
• Low total harmonic distortion
• Reduces ripple current in the storage capacitor between
the PFC and PWM sections
• Average current, continuous boost leading edge PFC
• Fast transconductance error amp for voltage loop
• High efficiency trailing edge PWM can be configured for
current mode or voltage mode operation
• Average line voltage compensation with brownout
control
• PFC overvoltage comparator eliminates output
“runaway” due to load removal
• Current fed gain modulator for improved noise immunity
• Overvoltage protection, UVLO, and soft start
General Description
The ML4824 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
IEC1000-2-3 specification. The ML4824 includes circuits
for the implementation of a leading edge, average current,
“boost” type power factor correction and a trailing edge,
pulse width modulator (PWM).
The device is available in two versions; the ML4824-1 (fPWM
= fPFC) and the ML4824-2 (fPWM = 2 x fPFC). Doubling the
switching frequency of the PWM allows the user to design
with smaller output components while maintaining the best
operating frequency for the PFC. An over-voltage compara-
tor 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 brown-out protection. The PWM
section can be operated in current or voltage mode at up to
250kHz and includes a duty cycle limit to prevent trans-
former saturation.
Block Diagram
16
VEAO
1
IEAO
VFB
15
2.5V
IAC
2
VRMS
4
ISENSE
3
VEA
–
+
3.5kΩ ^IEA
+
–
GAIN
MODULATOR
3.5kΩ
POWER FACTOR CORRECTOR
OVP
+
2.7V –
+
–
–1V +
–
PFC ILIMIT
VCCZ
13.5V
13
VCC
7.5V
REFERENCE
VREF
14
SQ
RQ
SQ
PFC OUT
12
RAMP 1
7
OSCILLATOR
RQ
RAMP 2
8
8V
x2
(-2 VERSION ONLY)
DUTY CYCLE
LIMIT
VDC
6
VCC
SS
5
50µA
8V
DC ILIMIT
9
1.25V
–
+
–
+
VIN OK
VFB –
1V –
2.5V +
+
DC ILIMIT
PULSE WIDTH MODULATOR
VCCZ
SQ
RQ
PWM OUT
11
UVLO
REV. 1.0.6 11/7/03