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This page helps the designer quickly find the right device and the values needed to build either positive or negative three pin regulator circuits.
Three pin adjustable IC regulators have a competitor in the form of the fixed three pin voltage regulator. The fixed three-pin regulator saves the electrical engineer much work and much sorrow. It does--all within one small three-lead package--what used to require at least a dozen discrete components and much design consideration. Whereas, PnP (plug and play) is pretty much the story with the fixed three-pin regulator. Maybe two small cheap bypass caps leading into the regulator and following it will be needed; that's about it.
All this begs the question: If these fixed regulators are so good why have the adjustable ones at all? The answer lies in flexibility and performance. Fixed three-pin regulators only come in a few preset voltages (3, 5, 6, 8, 9, 10, 12, 15, 18, 20 vdc). Whereas an adjustable three-pin regulator can be set to any voltage from 1.25v to 350v by changing the value of one or two resistors. If a 12.6 volt regulated supply is needed, the fixed three-pin regulator would strike out as that is not a currently available value--in spite of a tube renascence; the best one could hope for would be to find a 12v regulator that was out of tolerance by +.6 volts. Whereas the adjustable three-pin regulator requires only two resistors to set its output at 12.6 volts. The down side to adjustable three-pin regulators lies in their increased cost and complexity. At least 2 resistors, 2 to 3 capacitors and 2 diodes are needed.
To design a regulator is simple enough in Audio Gadgets. Enter or press the small up and down arrows next to the "Voltage" box until the desired voltage is displayed. Any value up to 350v for a positive regulator is acceptable. The idle current of an adjustable three-pin regulator can be as little as few ma's or as high as a few hundred ma's. Enter or press the small up and down arrows next to the "Idle Current" Box until the desired current in ma's is displayed. Audio Gadgets will do the rest; the program takes into account the leakage current through the adjustment pin and the drop out voltages.
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