Three Terminal, Adjustable, Regulators J. Michael Mooney Precise Voltage Selection and Rock Solid Regulators INSERT ILLUSTRATION The LM317 has a 1.5 Amperes maximum output, while the LM350 can handle 3 Amps. and the LM338- 5 Amps. All are wired as in the above schematic. Be sure to use a heatsink as these regulators will get hot if run near their maximum output. These devices will regulate within 1.5 to 2 Volts of the supply voltage. For example, with a 15 VDC input, the maximum voltage output of the regulator will be about 13 VDC. You can pick up the LM317($2), a heat sink, and resistors at Radio Shack. When you have the circuit put together, give it the following workout; 1. Using a well charged 12 Volt battery for input, and a good digital voltmeter - set the output to 11.00 Volts. 2. Load the output with a 1 Amp load and watch the voltmeter as you apply and remove the load. Isn't that nice? 3. Now, leaving the circuit JUST AS IT IS, series a second 12 Volt battery into the input circuit raising the input to 27.5 Volts. Cycle your load on and off again. THAT'S LINE/LOAD REGULATION! In a project box, this regulator is a terrific voltage source. In a circuit, with a fixed resistor in place of the pot it's a rock solid regulator. Internal protection effects a shutdown if thermal overload and/or current overload occurs, operation resumes afterward. It's almost indestructible. The basic regulator circuit above merely scratches the surface for this IC. Contact your nearest NATIONAL SEMICONDUCTOR Branch Office for the following application notes on the products; 1. LM338 POWER REGULATOR FAMILY - GENERAL DESCRIPTION. 2. AN-178 ADJUSTABLE IC POWER REG. 3. LB-35 3-TERMINAL REG. FOR BATTERY CHARGING. 4. LB-46 REGULATOR TRIMMING. *No doubt, these ICs will be incorporated into low voltage and cordless appliances so that they operate from any DC of ac power source in the 1.25 to 35 Volt range. A single 35 Volt design will emerge for all "ac Adaptors". J. Michael Mooney is a PV consultant with B&M Distributing, POB 667, Heavener, OK 74937 or call 501-441-7098.