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Power Factor Correction (PFC) and PWM Controller Combo
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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 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 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 transformer saturation.
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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
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