
2005 Fairchild Semiconductor Corporation
www.fairchildsemi.com
Rev. 1.0.0
Features
Low start-up current(100
μ
A typ.)
Low operating current(2.5mA typ.)
Low total harmonic distortion, high power factor
Pin-compatible upgrade for the ML4800
Average current, continuous, or discontinuous boost
leading edge PFC
Slew rate enhanced transconductance error
amplifier for ultra-fast PFC response
Internally synchronized leading edge PFC and
trailing edge PWM
Reduction of ripple current in the storage capacitor
between the PFC and PWM sections
PWM configurable for current mode or voltage mode
operation
Additional folded-back current limit for PWM section
20V BiCMOS process
VIN OK guaranteed turn on PWM at 2.25V
Vcc OVP Comparator, Low Power Detect
Comparator
Current-Fed gain modulator for improved noise
immunity
Brown out control, over-voltage protection, UVLO,
soft start, and Reference OK
Available in a 16-DIP Package
Applications
Desktop PC Power Supply
Internet Server Power Supply
Un-interruptible Power Supply UPS
Battery Charger
DC Motor Power Supply
Monitor Power Supply
Telecom System Power Supply
Distributed Power
General Description
The FAN4800 is a controller for power
factor
corrected,
switched
mode power supplies. Power Factor Correc-
tion (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 the IEC-1000-3-2 specifications.
Intended as a Bi-CMOS version of the industry-stan-
dard ML4800, the FAN4800 includes circuits for the
implementation of leading edge, average current, boost
type power factor correction and a trailing edge, pulse
width PWM (Pulse Width Modulator). A gate driver with
1A capabilities minimizes the need for external driver
circuits. Low power requirements improve efficiency
and reduce component costs.
An over voltage comparator shuts down the PFC sec-
tion 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.
The FAN4800 includes a folded-back
current limit for
the PWM section to provide a short circuit protection
function
.
16-DIP
FAN4800
Low S tart-Up Current PFC/PWM Controller Combos