AN4214 Datasheet, PDF (1/37 Pages) STMicroelectronics – High power factor flyback converter using the L6564

AN4214
Application note
High power factor flyback converter using the L6564
Harjeet Singh
Introduction
This application note describes the example of single stage high power factor (HPF) flyback
topology using ST’s L6564 PFC controller. The L6564 is a current mode PFC controller
operating in transition mode (TM). The highly linear multiplier, along with a special
correction circuit that reduces crossover distortion of the mains current, allows wide range
mains operation with an extremely low THD, even over a large load range. The main
drawback of such flyback topology with HPF is that it has significant magnitude of twice the
mains frequency ripple at output DC voltage because there is no electrolytic capacitor after
bridge rectification. But there are some applications like lighting for LED driving, battery
chargers, where ripple voltage is not a big concern, since in these applications the loads are
mostly constant-current driven with acceptable ripple or any kind of load which is powered
through followed DC-DC downstream converters connected to output of HPF flyback.
The output voltage is controlled by means of a voltage mode error amplifier and an accurate
(1% at Tj = 25 °C) internal voltage reference. The loop stability is optimized by the voltage
feedforward function (1/V² correction), which in this IC uses a proprietary technique that
considerably improves line transient response as well in case of both drops and surges
(“bidirectional”) of the mains.
In addition to overvoltage protection being capable of controlling the output voltage in the
PFC stage during transient conditions, the IC also provides protection against feedback loop
failures or erroneous settings. The feature is quite useful in case of flyback operation to
detect output voltage for any primary auxiliary winding and trigger the protection to
shutdown the converter in case output voltage exceeds the nominal value.
Other on-board protection functions allow brownout conditions and magnetic saturation to
be safely handled. The brownout is sensed through the MULT pin to shut down the
converter in case the input mains supply drops below the minimum operating voltage level.
The L6564 main features are:
 Fast “bidirectional” input voltage feedforward (1/V² correction)
 Accurate adjustable output overvoltage protection
 Protection against feedback loop disconnection (latched shutdown)
 Inductor saturation protection
 AC brownout detection
 Low (100 µA) start-up current
 6 A max. operating bias current
 1% (at T_J = 25 °C) internal reference voltage
 -600/+800 mA totem pole gate driver with active pull-down during UVLO
 SSOP10 package
January 2015
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