12 Volt Low Voltage Droput Precision Regulator with LM324

Most regulator circuits require at least 3 to 5 volts between input and output to operate reliably. This regulator features a P-Channel MOS-FET pass element that will allow for a very low drop out voltage. In my particular application reliable operation was noted down to nearly 0.1 volt between input and output at nearly 0.8 amperes of load current. Useful applications include automotive and battery applications were regulation is desired and available input-output differential is less than 0.5 V. By using the LM324 Op-Amp and the LM336 Precision Reference Diode, both single supply operation and precision output regulation were easily achieved.
I originally designed this for a 12V camera. The camera was a surplus property item and contained only the camera and a small adapter box. The 1″ x 2″ 1″ adapter box contained a connector from which video, audio and power adapter connectors were attached. My intent was to use a 12V 1 amp adapter from Radio Shack to power the camera. Unfortunately the adapter provided an unregulated 15V under no load and slightly more than 12.3V under full load. This necessitated the use of a very low drop-out regulator circuit. By using a MOS-FET I could minimize the drop-out voltage and have the added benefit of very low power dissipation. This design allowed for minimal heatsinking and could be packaged very tightly in nearly any small enclosure. In my final design the entire regulator circuit fit easily in the 1″ x 2″ x 1″ adapter case.

Read More Source :http://www.drbob.net/project/powersupply/linear/12v1alvdfxd/default.html

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