AN1060 Datasheet, PDF (1/11 Pages) STMicroelectronics – FLYBACK CONVERTERS WITH THE L6561 PFC

AN1060
®
APPLICATION NOTE
FLYBACK CONVERTERS WITH THE L6561 PFC
CONTROLLER
by C. Adragna & G. Gattavari
The L6561, controller specifically designed for Power Factor Correction (PFC) circuits, may be suc-
cessfully used in flyback converters as well.
The excellent performance of the device, along with its characteristics in terms of low current con-
sumption, makes L6561-based flyback converters really attractive in medium-low power applications.
There are basically three different configurations that an L6561-based flyback converter can assume,
each of them with its own characteristics, benefits and peculiarities. This paper describes these con-
figurations and highlights advantages/drawbacks with the aim of identifying the most suitable appli-
cations they can fit.
INTRODUCTION
Common practice bounds their use in conventional boost PFC stages, yet Transition Mode (TM) Power
Factor Corrector IC’s can be used in applications different from those they are primarily intended for.
This is particularly true for the L6561, PFC controller for medium-low power applications, because of its
peculiar characteristics.
Reference [2] presents a special example showing how to extend the use of this device to Mag Amp ap-
plications.
Figure 1 - L6561 Internal Block Diagram
1
INV
-
2.5V
+
COMP
2
MULT
3
MULTIPLIER
CS
4
40K
VOLTAGE
REGULATOR
OVER-VOLTAGE
DETECTION
+-
5pF
8
V_CC
20V
R2
INTERNAL
SUPPLY 7V
R1
+
-
V_REF2
2.1V
1.6V
UVLO
RQ
S
DRIVER
ZERO CURRENT
+ ^DETECTOR
-
STARTER
V_CC
7
GD
6
GND
5
ZCD
DISABLE
D97IN547D
The outperforming L6561 offers a number of unique advantages that make the device an interesting al-
ternative to the traditionally used PWM controllers where quite a good performance is required at low
cost:
January 2003
1/11