FairchildFAN6863反激電源PWM控制方案

Fairchild 公司的FAN6863是高度集成的反激電源綠模式PWM控制器，設(shè)計(jì)用在小于40W和待機(jī)功耗小于100mW的消費(fèi)類電子產(chǎn)品如適配器，機(jī)頂盒（STB），上網(wǎng)本等. FAN6863的起動(dòng)電流為8uA，綠模式（Green Mode）的工作電流600uA，具有軟驅(qū)動(dòng)以降低EMI，主要用在通用的開關(guān)電源和反激電源轉(zhuǎn)換器。本文介紹了FAN6863主要特性，方框圖以及起動(dòng)電路圖和應(yīng)用電路圖。

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應(yīng)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

圖1。FAN6863方框圖

圖2。FAN6863典型應(yīng)用電路圖

圖3。FAN6863起動(dòng)電路圖

圖4。FAN6863詳細(xì)的應(yīng)用電路圖

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