Yesterday we got an interesting picture from one of our customer showing an application of SMR8812 driving a 12V fan and SMR8805 driving an android mini tv box using a single IBM laptop power supply.
Minggu, 08 September 2013
In this application we would like to re-use common switching supply that been use for printer, or LCD, mostly come with 19V or 24V, for charging a 12V battery.
The original circuit is adapted from eleccircuit 12v charger.
Basic idea is remain the same from the original circuit, a comparator is use to detect if the battery voltage has been lower than what has been set by potentiometer VR and value of zener diode ZD1, when comparator is high, it will set transistor Q to ON to drive relay. The relay will set connection from DC input into SMR8814, D1 will limit surge current and provide polarity protection, since SMR8814 is a fix 14v switch mode dc converter, adding a D2 will drop the voltage to approximately 13,5-13,8v to charge the battery, it will also prevent the battery current to reversely damage the charging power supply.