FairchildFAN6863反激电源PWM控制方案

Fairchild 公司的FAN6863是高度集成的反激电源绿模式PWM控制器，设计用在小于40W和待机功耗小于100mW的消费类电子产品如适配器，机顶盒（STB），上网本等. FAN6863的起动电流为8uA，绿模式（Green Mode）的工作电流600uA，具有软驱动以降低EMI，主要用在通用的开关电源和反激电源转换器。本文介绍了FAN6863主要特性，方框图以及起动电路图和应用电路图。

FAN6863：Highly Integrated Green-Mode PWM Controller

A highly integrated PWM controller, FAN6863 provides several features to enhance the performance of flyback converters. To minimize standby power consumption, a proprietary Green Mode provides off-time modulation to continuously decrease the switching frequency under light-load conditions. Under zero-load conditions, the power supply enters Burst Mode, which completely shuts off PWM output. Output restarts just before the supply voltage drops below the UVLO lower limit. Green Mode enables power supplies to meet international power conservation requirements.

The FAN6863 is designed for SMPS and integrates a frequency-hopping function that helps reduce EMI emission of a power supply with minimum line filters.

The built-in synchronized slope compensation provides proprietary sawtooth compensation for constant output power limit over universal AC input range. The gate output is clamped at 13.5V to protect the external MOSFET from over-voltage damage.Other protection functions include SENSE pin Short- Circuit Protection (SSCP), VDD Over-Voltage Protection (OVP), and Over-Temperature Protection (OTP). For OTP, an external NTC thermistor can be applied to sense the ambient temperature. When VDD OVP or OTP is activated, an internal latch circuit latches off the controller.

FAN6863主要特性：

Low Standby Power: Under 0.1W

Low Startup Current: 8μA

Low Operating Current at Green Mode: 600μA

Peak-Current Mode Operation with Cycle-by-Cycle Current Limiting

PWM Frequency Continuously Decreasing with Burst Mode at Light Loads

VDD Over-Voltage Protection (OVP)

Constant Output Power Limit (Full AC Input Range)

Internal Latch Circuit (FAN6863L) for OVP, OTP

SENSE Pin Short-Circuit Protection (SSCP)

Fixed PWM Frequency (65KHz) with Frequency Hopping

Feedback Open-Loop Protection: 60ms Delay

GATE Output Maximum Voltage Clamp: 13.5V

Soft-Start Time: 5ms

Soft Driving for EMI Improvement

Full Range Frequency Hopping

Internal OTP Sensor with Hysteresis
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GATE Driving Capability: 400mA

FAN6863应用：

General-purpose switched-mode power supplies and flyback power converters, including:
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Power Adapters
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Open-Frame SMPS
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SMPS with Surge-Current Output, such as for Printers, Scanners, Motor Drivers

图1。FAN6863方框图

图2。FAN6863典型应用电路图

图3。FAN6863起动电路图

图4。FAN6863详细的应用电路图