Power supply on the LM78H12K chip, 12 volts 5 amps. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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A powerful power supply can be assembled based on modern integrated circuits. On the LM78H12K integrated circuit, a 12 V source with a maximum current of 5 A is obtained. The microcircuit is protected against short circuits, overtemperature and withstands a short-term current up to 7 A. This source can be used, for example, to power an ultrasonic frequency converter or other devices.

The source diagram is shown in Fig.1.

The alternating voltage from the secondary winding of the transformer T1 is supplied to a powerful diode bridge VD1, designed for a rectified current of at least 5 A. After the diode bridge, the rectified voltage is supplied to the capacitors C1 and C2, which perform low-frequency and high-frequency voltage filtering, and then to the input of the stabilizer microcircuit DA1.

The microcircuit is made in a metal case TO-204 (TO-3) with two leads (input and output). The microcircuit housing serves as a control output and is connected to the circuit through screws and adapter pads on the printed circuit board. On this microcircuit, you can assemble a linear voltage regulator operating in low dropout mode, with an output voltage of 2,3 V at a current of up to 5 A. From the output of the DA1 microcircuit, the stabilized voltage is supplied to capacitors C3, C4 and then to the power supply output. The indicator on the HL1 LED performs service functions, i.e. shows the voltage supply to the stabilizer circuit board.

The printed circuit board of the source (Fig. 2) is made of one-sided foil fiberglass with a thickness of 1,5 ... 2 mm and dimensions of 60x60 mm.

The location of the radio components on the board is shown in Fig.3.

After the board is made, the current-carrying tracks, especially the power ones, must be well tinned with solder. On the printed circuit board, there is free space for installing a radiator when the microcircuit is operated in extreme modes.

The types of parts used are shown in the table. The transformer for the source is selected in accordance with the current load and, recommended, with a voltage of the secondary winding of 17 ... 20 V. A fuse with a rated current of 0,5 ... 1 A must be installed in the primary circuit of the transformer. thick stranded wire with good insulation, and a computer network wire with an euro plug is best suited as a network wire.

At high loads, the diode matrix and the stabilizer microcircuit are installed on radiators of the appropriate sizes. For these purposes, the DA1 chip is specially located separately from the rest of the radio components, this allows you to install a radiator with the required dissipation area. After mounting and testing the source, it is desirable to varnish the printed circuit board.

Author: A. Lechkin, Ryazan

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