Document
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
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Internally synchronized leading-edge modulated PFC and trailing-edge modulated PWM in one IC TriFault DetectTM for UL1950 compliance and enhanced safety VCCOVP 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
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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
ML4804
PIN CONFIGURATION
ML4804 16-Pin PDIP (P16) 16-Pin Narrow SOIC (S16N)
IEAO 1 IAC 2 ISENSE 3 VRMS 4 SS 5 VDC 6 RAMP 1 7 RAMP 2 8 16 VEAO 15 VFB 14 VREF 13 VCC 12 PFC OUT 11 PWM OUT 10 GND 9 DC ILIMIT
TOP VIEW
PIN DESCRIPTION
PIN NAME FUNCTION PIN NAME FUNCTION
1 2 3 4 5 6 7 8
IEAO IAC I SENSE V RMS SS VDC RAMP 1 RAMP 2
Slew rate enhanced PFC transconductance error amplifier output PFC AC line reference input to Gain Modulator Current sense input to the PFC Gain Modulator PFC Gain Modulator RMS line voltage compensation input Connection point for the PWM soft start ca.