Power Factor Correction and PWM Controller Combo
June 1998
ML4824* Power Factor Correction and PWM Controller Combo
GENERAL DESCRIPTION
The ML4824 is a controller for p...
Description
June 1998
ML4824* Power Factor Correction and PWM Controller Combo
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 t
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hat 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 brownout 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.
FEATURES
s s s
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
s s s
s
s
s s
BLOCK DIAGRAM
16
1
*Some Packages Are Obsolete
13
VEAO VFB
VEA –
+
–
IEAO
POWER FACTOR CORRECTOR
OVP
3.5kΩ
+
VCCZ
13.5V
VCC
15
2.5V
IEA
+ –
+
2.7V
–
7.5V REFERENCE
S Q Q
VREF
14
IAC
2
VRMS
4
GAIN MODULATOR
3.5kΩ
–1V
+ –
R
S R
PFC OUT
ISENSE
3
PFC ILIMIT
Q Q
12
RAMP 1
7
RAMP 2
8
8V
OSCILLATOR
(-2 VERSION ONLY) x2
DUTY CYCLE LIMIT
VDC
6
VCC
1.25V
– +
–
S
VFB
– +
Q Q
PWM OUT
11
VIN OK
SS
5
50µA
+
1V
– +
2.5V
8V
R
DC ILIMIT
DC ILIMIT
9
PULSE WIDTH MODULATOR
VCCZ
UVLO
1
ML4824
PIN CONFIGURATION
ML4824 16-Pin PDIP (P16) 16-Pin Wide SOIC (S16W)
IEAO IAC ISENSE VRMS SS VDC RAMP 1 RAMP 2 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 VEAO VFB VREF VCC PFC OUT PWM OUT GND DC ILIMIT
TOP VIEW
PIN DESCRIPTION
PIN NAME FUNCTION PIN NAME FUNCTION
1 2 3 4 5 6 7 8
IEAO IAC ISENSE VRMS SS VDC RAMP 1 RAMP 2
PFC transconductance current error amplifier output PFC gain control reference input
9 10 11
DC ILIMIT GND
PWM current limit comparator input Ground
PWM OUT PWM driver output PFC OUT VCC VREF VFB VEAO PFC driver
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