AN4129

www.DataSheet4U.com www.fairchildsemi.com Application Note AN4129 Green Current Mode PWM Controller FAN7601 1. Introduction This application note describes the operation and features of the FAN7601. This device is a BCDMOS programmable frequency current mode PWM controller which is designed for off-line adapter applications and auxiliary power supplies. To reduce power loss at light and no load, the FAN7601 operates in burst mode and it includes a start-up switch to reduce the losses in the start-up circuit. Because of the internal start-up switch and burst mode operation, it is possible to supply an output power of 0.5W with under 1W input power when the input line voltage is 265V. On no load condition, input power is under 0.3W. The FAN7601 offers a latch protection pin for the protection of the system e.g. over voltage protection and/or thermal shutdown. The internal over voltage protection function shuts down the IC operation when the supply voltage reaches 19V. In addition, a soft start function is provided, and the soft start time can be varied. Figure 1 shows a block diagram for the FAN7601. It contains the following blocks. Start-up circuit and reference Oscillator Soft start and latch Current sense and feed back Burst mode Output drive Vref 8 Vstr 1 7 Vcc 5V Ref Enable Start-up Circuit UVLO OVP + − 19V Rt/Ct 4 OSC Vref 12uA S Q R + − 12V/8V Latch/SS 3 1.5V OVP 6 OUT + − 2.5V S Q R Delay Circuit + − 0.97V/0.9V 2 CS/FB 1V GND 5 + − Star...