Revision 11/24/2015

Preliminary and all contents are subject to change without prior notice.

© Seaward Electronics, Inc., 2006. • www.seawardinc.com.cn • Page 5

Start Up and Short Circuit Conditions

Under start-up or short-circuit conditions the SE1051 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 SE1051 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 SE1051 (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

SE1051 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.

Fig. 3