12V Car Charger for ASUS Eee Notebook

This charger is built around the LM2576 Simple Switcher IC which can power any device from a car or 12V SLA battery.

The design of the charger contains a low voltage cut-out based on a 9.1V Zener diode and BC337 transistor. If the input voltage is below 11.5V, the transistor will shut down the regulator in order to help prevent accidental flattening of the supply battery and to prevent unstable operation of the regulator at lower input voltages. The cut-out voltage may get affected if the transistor is substituted for similar type.

A standard 3-pin regulator IC like the LM317 could have been used but it will require an external transistor when so much current is handled since they are very inefficient. Heat is dissipated as the difference in power since they draw the same amount of current from the input as the load.

To help provide more stable operation and better efficiency of the charger, the capacitors to be used must have high temperature and low ESR. A small plastic enclosure was used for a case since the PCB was designed to be fitted but any small casing will do.

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