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-FEBUARY NEWS LETTERIsotron 40 A video description of how it works. MAKING A SMALL REGULATED POWER SUPPLY There are times when we need a well regulated low wattage power supply. Say, no more than 15 watts. This is good for operating a hand held transceiver, antenna analyzer, trickle chargers, audio amps, relays and more. What can you use and what parts work well? There are several solid state regulator devices. To start, the easiest to use is the LM78xx or LM79xx series. You find these as low as 50 cents each. These will handle 1 to 1.5 amps at the voltage you select. If you want a + voltage, then select the LM78xx series. A - voltage, the LM79xx series. The xx is the voltage desired. A LM7805 will supply a 5 volt + source. A LM7905 provides a 5 volt - source. These devices are normally a TO-220 case. What is that? This is a case of a flat rectangular wafer, about 3/8" width, 5/8" length and 3/16" thick. It is made to mount on a heat sink, however for currents within its range, the heat sinks are seldom used. There are 3 leads coming out the 3/8" side of the wafer. If you position the wafer so the lettering is toward you and the leads are down, it is easy to determine the function of each lead. The lead to your left is the Input. The center lead connects to Ground or the opposite polarity. The right lead is your regulated Output. ┌─────────┐ │ o │HEAT SINK MOUNTING HOLE ├─────────┤ │ │ │ │ │ │ │ │ └┬───┬───┬┘ │ │ │ IN │ │ │ OUT GND
FIGURE 1
The "IN" lead can be supplied with as high as 40 volts. This will need to be a rectified voltage with a + polarity for the 78 series. A small transformer or wall wart can be used. If a transformer is used, a full wave rectifier should be next in the circuit. This voltage can be filtered with an electrolytic capacitor of at least 500 mf (C1) across the rectifier.
│ │ └─┬──┬──┬┘ IN │ │ │OUT +o────────┬──────┘ │ └───┬───────+ 40V MAX C1 ──┴── GND │ ───┴─── C2 REGULATED OUT ──┬── │ ───┬─── -o────────┴─────────┴──────┴──
FIGURE 2 The "OUT" lead should have a filter capacitor (C2) of 1,000 mf or more. This simple circuit will provide you with a very stable and smooth rectified voltage of your selection. 73, Ralph WD0EJA 12-15 BILAL COMPANY 137 MANCHESTER DR. FLORISSANT, CO. 80816 U.S.A PH/FX: 719/687-0650 OUR EMAIL LIST IS ACQUIRED BY PERSONS WHO HAVE CONTACTED US IN THE PAST. IF YOU DESIRE NOT TO BE CONTACTED PLEASE EMAIL YOUR request at http://wd0eja@isotronantennas. PHOTO WAS TAKEN 10 MILES SW OF FLORISSANT, CO. |
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