FAN6751 is a highly integrated PWM controller produced by Fairchild Semiconductor. It has multiple features to enhance the performance of LCDM/TV, NB and adapters. The green-mode function includes off-time modulation and burst mode to reduce the PWM frequency at light-load and in no-load conditions. To avoid acoustic noise problems, the minimum PWM frequency is set above 18KHz. This green-mode function enables the power supply to meet international power conservation requirements. With the internal high-voltage startup circuitry, the power loss due to bleeding resistors is also eliminated. Built-in synchronized slope compensation achieves stable peak-current-mode control. The proprietary external line compensation ensures constant output power limit over a wide AC input voltage range, from 90VAC to 264VAC. FAN6751 provides many protection functions, as shown in Table 1. In addition to cycle-by-cycle current limiting, the internal open-loop protection circuit ensures safety should an open-loop or output short-circuit failure occur.
The document is an application note (AN-6073) detailing the design of a high-efficiency, compact flyback converter using the Fairchild FAN6751 series of PWM controllers. It highlights features such as off-time modulation and burst mode for light-load conditions to meet power conservation requirements, along with internal protection circuits like open-loop protection and over-voltage protection.
The note provides detailed design strategies including startup and soft-start circuitry, under-voltage lockout (UVLO) specifications, feedback circuit configuration, and the implementation of synchronized slope compensation for stable peak-current-mode control in continuous conduction mode.
| Low Operating Current | 4mA |
|---|---|
| Minimum PWM Frequency | 18KHz |
| Gate Output Maximum Voltage Clamp | 18V |
| Turn-on Threshold Voltage (VDD) | 16.5V |
| Turn-off Threshold Voltage (VDD) | 10.5V |
The minimum PWM frequency is set above 18KHz to avoid acoustic noise problems.
The minimum PWM frequency is set above 18KHz.
The maximum sourcing current of the FB pin is 1.5mA.
The internal limit Vsrnsz is 0.83V typically.