DatasheetQ Logo
Electronic component search and free download site.
Transistors,MosFET ,Diode,Integrated circuits

KA7526 View Datasheet(PDF) - Fairchild Semiconductor

Part Name
Description
Manufacturer
KA7526
Fairchild
Fairchild Semiconductor Fairchild
KA7526 Datasheet PDF : 22 Pages
1 2 3 4 5 6 7 8 9 10 Next Last
KA7526
Operating Description
KA7526 is high performance, critical conduction, current-mode power factor controller specifically designed for use in off-
line active preconverters with minimal external components. This device provides the necessary features which are required to
significantly en-hance poor power factor loads by keeping the ac line current sinusoidal and in phase with the line voltage.
KA7526 contains many of the building blocks and protection features that are employed in modern high performance current
mode power supply controllers. A description of each of the function blocks is given below.
START-UP
An Undervoltage Lockout comparator has been incorporated to guarantee that IC is fully functional before enabling the output
stage. The positive power supply terminal (Vcc) is monitored by the UVLO comparator with the upper threshold set at 13V
and the lower threshold at 8V. In the stand-by mode, with Vcc at 12.5V, the required supply current is less than 0.3mA . This
large hysteresis and low start-up current allow the implementation of efficient bootstrap start-up techniques, making this
device ideally suited for wide range off-line preconverter applications.
Fig.1.1 shows the start-up circuit. Circuit operation is as follows:
The start-up capacitor (Cst) is charged by current through start-up resistor (Rst) minus the start-up current drawn by the IC.
Once the capacitor voltage reaches the start-up threshold, the IC turns on, starting the switching of the MOSFET. The opera-
tion of the IC demands an increase in operating current which results in discharging the capacitor. Before the start-up capacitor
voltage is discharged below hysteresis voltage, the auxiliary winding voltage takes over as the supply voltage as shown in Fig.
1.2.
AC
input
Rst
+
Cst
DVcc
Vcc
Out
KA7526
Fig.1.1 Start-up Circuit
Vcc
Vstart
Hysteresis
Cst discharges
Cst charges
from Rst
t
Fig.1.2 Start-up Capacitor Voltage
10
 

Share Link: 

datasheetq.com  [ Privacy Policy ]Request Datasheet ] [ Contact Us ]