Start Up and Short Circuit Conditions
Under start-up or short-circuit conditions the SE1052 does not have a high enough supply voltage. This is
due to the fact that the chip has its power supply line in common with the power supply line of the charger
system. Consequently, the current limitation can only be ensured by the primary PWM module, which
should be designed accordingly.
If the primary current limitation is considered not to be precise enough for the application, then a sufficient
supply for the SE1052 has to be ensured under any condition. It would then be necessary to add some
circuitry to supply the chip with a separate power line. This can be achieved in numerous ways, including an
additional winding on the transformer.
The following schematic shows how to realize a low-cost power supply for the SE1052 (with no additional
windings).
Please pay attention to the fact that in the particular case presented here, this low-cost power supply can
reach voltages as high as twice the voltage of the regulated line. Since the Absolute Maximum Rating of the
SE1052 supply voltage is 18V, this low-cost auxiliary power supply can only be used in applications where
the regulated line voltage does not exceed 9V.
To primary
Vcc
Rs
1.210 V
Vout+
R2
SE1052
Output
Rout
C2
22 p F
Rvc1
Cvc1
2.2nF
Cs
100mV
Vctrl
Cic1
2.2nF
Ric1
Rled
1K
LED_R
10mV
R1
Red
Ictrl
Vsense
Rsense
GND
Ric2
Green
LED_G
Vout-
Note：0 ohms of Ric2 is recommended for LED charging indication function.
Revision 5/7/2009
Preliminary and all contents are subject to change without prior notice.
© Seaward Electronics, Inc., 2006. • www.seawardinc.com.cn • Page 6
SEAWARD [ Seaward Electronics Inc. ]
