Power Filter- Regulator Circuit With LM1084

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My friend want Circuit Filer power supply for Car.
I test is circuit Filer CAR power supply, Use IC LM1084 - 5A Low Dropout Positive Regulators.
It is small circuit and easy to build, Detail more see in image circuit.

I to see web : http://linuxcar.sone.jp/reg.en.html
good idea circuit.
read simple ::
At input side of regulator, I inserted a series inductor in addition to normal decoupling capacitor to form a LC filter, so that it can resist transient voltage. If supply voltage temporary goes up, it can be absorbed by regulator. But if it goes down below 13V, regulator can’t do anything but drops its output voltage. If an inductor is there, it prevents capacitor from discharging into battery side, keeping regulator’s input voltage high. It also prevents noise emission, smoothing the PC’s pulse-ish current consumption.

Additionally, I added a surge suppressor diode (20V) designed especially for car electronics, to protect regulator from higher voltage than its maximum input (30V). Also a DC line filter is inserted just after the input from car, to eliminate high frequency noise.
Schematic diagram of power filter/regulator circuit

The diode between output and input of LM1084 is to protect regulator when supply voltage suddenly drops down and the potential difference becomes reverse. Be sure to choose values of inductor (L) and capacitor (C) at input side so that L/C is small enough. If not, large overshoot/undershoot voltage is caused by load transient. Besides large chemical capacitor, I also put a couple of 0.1ÂµF multi-layer ceramic capacitor near the regulator, to stabilize it against high frequency transient.

Relay is at after the regulator, because controller circuit needs regulated and backed-up power. Because of this, regulator is always connected to the battery. I measured the current with no load, it was 5.2mA. It was more than I expected, but I checked the datasheet and it says 5mA typical. I became a little anxious about the battery, and calculated, then it was less than 1Ah if I leave the car for 1 week. Car battery is 40Ah, 55Ah or something like that, that was no problem, after all.

This entry was posted on Tuesday, July 10th, 2007 at 12:44 pm and is filed under Power supply. You can follow any responses to this entry through the RSS 2.0 feed.