This circuit design is inspired by National Semiconductor's application notes. The first section consists of three voltage regulators, LM338 [IC1-2-3], connected in parallel. Each regulator can provide up to 5 amperes, and the combined output voltage ranges from +4.5V to 25V DC, which remains stable. The voltage regulation at the output is achieved using TR1. If continuous output voltage regulation is unnecessary, the resistance value of trimmer TR1 can be measured and replaced with an equivalent fixed resistor corresponding to the desired output voltage. The rectifier bridge, BR1, should be mounted on a metal box to ensure proper cooling. Conversely, the IC1-2-3 units, which come in TO-3 cases, should be mounted on appropriately sized heat sinks, with mica insulation between them and the heat sink. Direct contact with the heat sink must be avoided to prevent short circuits. Resistors R1-2-3 should be placed away from the PCB due to their heat generation, reducing the risk of damaging the board. Attention should also be paid to the thick cables carrying high currents, ensuring they have sufficient diameter and are properly routed to avoid short circuits. In the second part of the diagram, there’s a simpler circuit based on the LM350 voltage regulator, which can deliver regulated voltages ranging from +1.25V to 25V DC with a maximum current of 3A. The IC5 is housed in a TO-3 case for better thermal conductivity and mounted on a heat sink with mica insulation. The output is adjusted via trimmer TR2. The circuit is powered by a power transformer larger than 450VA. The assembled circuit should be placed in a suitably-sized box with good ventilation. A 12x12 cm fan operating on 230Vac can assist in expelling excess heat. Ammeters and voltmeters can be installed at the outputs. Small details such as R1-2-3 = 0.1Ω 5W, C3-5-8-10 = 100nF 100V MKT, IC1-2-3 = LM338 [TO-3 case] on Heat Sink, R4 = 100Ω 0.5W, C4 = 220pF 100V ceramic, IC4 = LM308, R5 = 150Ω 0.5W, C6-11 = 47μF 63V, IC5 = LM350 [TO-220 or TO-3 case] on Heat Sink, R6-8 = 330Ω 0.5W, C7 = 4700μF 63V, J1 = 3-terminal block computer type, R7-9 = 4.7KΩ 0.5W, C9 = 10μF 40V, J2-3-4-5 = 2-pin connector 3.96mm step pin, R10-13 = 1.5KΩ 0.5W, D1-2 = LED Red 5mm, F1 = Fuse 5A slow block, R11-12 = 220Ω 0.5W, D3 = 1N4007, T1 = 230Vac/22Vac 600VA transformer, TR1 = 1.5KΩ trimmer, BR1 = Bridge Rectifier >250V 35A on Heat Sink, TR2 = 4.7KΩ trimmer, BR2 = Bridge Rectifier >250V 3A, uF = microfarad, R = ohms, K = kilohms, C-2 = 10000μF 63V, Q1 = 2N2905 are all important components listed below the main text.
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