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 TE Connectivity

  • Car to PC Power Filter and Regulator

  • Created: Aug 20, 2015

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Ideally, the normal voltage of a car battery is around 12V; however, in reality, it has an appreciable amount of fluctuations. When the engine is off, the voltage settled around 12V, but once the engine starts, it drops down to 6-8V due to huge load and engine cranking. Noises from alternator, motors, and other electrical loads are the primary contributors to the voltage fluctuations when the engine is running. Because of these fluctuations, it is dangerous to hook a car battery up directly to a computer. Thus, a circuit is needed to convert car supply voltage to a regulated 12V. A power line filter is needed to protect the computer from these voltage fluctuations. A power line filter, also called as EMI suppression filter, is an electronic component that provides electromagnetic noise suppression for electronic devices and is used with electronic shields and other circuit protection components.

Now that the voltage is regulated at 12V, it would need a switch mode regulator to step up the voltage. In this circuit, a low-dropout regulator is used to convert voltage higher than 13V to 12V. This regulator operates at about 1V dropout, and can supply 5A maximum. An LC filter is inserted at the input side of the regulator so that it can resist transient voltage. The inductor prevents capacitor from discharging into the battery side, keeping the voltage high. The surge suppressor diode (D1), designed particularly for car electronics, is added to protect the regulator from higher voltage than its maximum input. The diode between the output and input of the regulator (D2) is to protect regulator when supply voltage suddenly drops down and the potential difference becomes reverse. The relay (TE Connectivity’s 9-1393113-8) is connected after the regulator because the controller circuit is always connected to a battery for a back-up power.

This circuit is specifically designed for car to PC, but it can also be used as power line filter and regulator to other applications in automotive industries. It is also useful in RF circuits that require protection against electromagnetic interference/ radio frequency interference.