AN2941 datasheet(11/37 Pages) STMICROELECTRONICS

11 / 37 page

AN2941

Main characteristics and circuit description

Doc ID 15447 Rev 4

11/37

Overtemperature protection

Thermistor R58, connected to L6566A DIS pin (#8), provides for a thermal protection of the

flyback MOSFET (Q5). The L6563S PWM_LATCH pin (activated in case of PFC loop

failures or PFC inductor saturation) is connected to L6566A DIS pin too. In case of PFC

latching failure, the flyback converter activity is latched too. To maintain this state

, an internal

circuitry of the L6566A monitors the VCC and periodically reactivates the HV current source

to supply the IC, while the L6563S remains inactive after latching because it is no longer

powered via the Vcc_PFC pin that has been opened by the internal L6566A logic.

Standby power savings

The L6566A implements a current mode control, thus it monitors the output power by pin

COMP whose level is proportional to the load. Thus, when the voltage on pin COMP falls

below an internal threshold, the controller is disabled and its consumption reduced. Normal

operation restarts as soon as the COMP voltage rises again. In this way a low consumption

burst mode operation is obtained.

On this board, because the flyback stage acts as master, it has been electrically designed to

operate over the entire mains voltage range. This solution allows turning off the PFC

controller during no-load operation, saving power. As soon as the COMP level falls below

the burst mode threshold, the L6566A stops supplying the PFC controller, disabling

VCC_PFC pin and reducing the PFC consumption to almost zero as already explained,

minimizing the overall consumption of the converter.

AN2941 Datasheet(PDF) 11 Page - STMicroelectronics