FairchildFAN6863 flyback power supply PWM control scheme

Fairchild’s FAN6863 is a highly integrated flyback power green-mode PWM controller, designed to be used in consumer Electronic products such as adapters, set-top boxes (STBs), netbooks, etc. with less than 40W and standby power consumption less than 100mW. The starting current of FAN6863 is 8uA , Green Mode (Green Mode) operating current 600uA, with soft drive to reduce EMI, mainly used in general switching power supplies and flyback power converters. This article introduces the main features of FAN6863, block diagram, start-up circuit diagram and application circuit diagram.

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 main features:

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

GATE Driving Capability: 400mA

FAN6863 application:

General-purpose switched-mode power supplies and flyback power converters, including:

Power Adapters

Open-Frame SMPS

SMPS with Surge-Current Output, such as for Printers, Scanners, Motor Drivers
FairchildFAN6863 flyback power supply PWM control scheme
figure 1. FAN6863 block diagram
FairchildFAN6863 flyback power supply PWM control scheme
figure 2. FAN6863 Typical Application Circuit Diagram
FairchildFAN6863 flyback power supply PWM control scheme
image 3. FAN6863 starting circuit diagram

Figure 4. FAN6863 detailed application circuit diagram
For details, see:

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