FAN6751HLMY Просмотр технического описания (PDF) - Fairchild Semiconductor

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FAN6751HLMY

Highly Integrated Green-Mode PWM Controller

Fairchild Semiconductor 

AN-6073

APPLICATION NOTE

Typical Application Circuit

Application

LCD Monitor

Power Supply

Output Power

44W

Input Voltage Range

Universal Input

(90-264VAC)

Output Voltage/Maximum Current

12V/2A

5V/4A

Features

ƒ High-Voltage Startup

ƒ Built-in 5ms Soft-Start Function

ƒ Built-in VIN Pin Pull-High (> 4.7V) Recovery Function for Second-Side Output OVP

ƒ Brownout Protection with Hysteresis

ƒ Low Standby Mode Power Consumption (Input Wattage <0.3W at No-Load Condition)

Key Design Notes

ƒ Resistors R12 and R13 work as a startup resistor to provide necessary current for IC startup. After startup, there is no

power loss on these resistors. The recommended values for R12 and R13 are 130KΩ(1/4W) and 51KΩ(1/4W).

ƒ Because the VIN pin is connected through a resistive divider R3 and R16 to the rectified AC input line voltage, it can also

be used for brownout protection. If the VIN voltage is less than 0.7V, the PWM output is shut off. As the VIN voltage

reaches 0.92V, the PWM output is turned on again. The hysteresis window for ON/OFF is 0.22V. The recommended

values for R3+R15, R16, and C16 are 10MΩ (5MΩ+5MΩ), 100KΩ, and 2.2µF. Using these values in the test board, the

power supply is turned off at 66V (maximum load) and recovered at 70V.

ƒ The secondary-side over-voltage protection (OVP) is achieved by pulling the VIN pin high. ZD1, ZD2, R29, R30, R31, R32,

C15, and U3 form a secondary-side over-voltage protection (OVP) circuit. When each output reaches OVP, photocoupler

U3 pulls the VIN pin high. The OVP voltages of the 12V-output and 5V-output are 15V and 6.8V, respectively.

© 2008 Fairchild Semiconductor Corporation

Rev. 1.0.0 • 9/26/08

Figure 23. Schematic

10

www.fairchildsemi.com

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