Powerful linear voltage regulatorTo power various electronic devices and circuits made by yourself, you need a power source, the output voltage of which can be adjusted within wide limits. With its help, you can observe how the circuit behaves at this or that supply voltage. At the same time, it should be able to produce a high current in order to feed a powerful load, and minimal pulsations at the output. The linear voltage regulator LM338 is suitable for the role of such a power source; it provides a current of up to 5 A, it has a protection against overheating and short circuit on the output. The scheme of its inclusion is quite simple, it is presented below.
SchemaThe LM338 has three outputs - input (in), out (out) and regulating (adj). At the input we supply a constant voltage of a certain size, and from the output we remove the stabilized voltage, the value of which is given by the variable resistor P2.The output voltage is adjustable from 1.25 volts to the input, with a deduction of 1.5 volts. Simply put, if the input, for example, 24 volts, then the output voltage will vary from 1.25 to 22.5 volts. Serve at the input of more than 30 volts should not be, the chip can go into protection. The more capacitors at the input, the better, because they smooth out the pulsations. The capacitance of the capacitors at the output of the microcircuit must be small, otherwise they will keep the charge for a long time and the output voltage will not be adjusted correctly. In addition, each electrolytic capacitor must be shunted with a film or ceramic with a small capacitance (in the diagram it is C2 and C4). When using a circuit with large currents, the microcircuit must be installed on the radiator, because it will dissipate all the voltage drops on itself. If the currents are small - up to 100 mA, no radiator is required.
Stabilizer assemblyThe whole circuit is assembled on a small printed circuit board with dimensions of 35 x 20 mm, which can be manufactured using the LUT method. The printed circuit board is completely ready for printing, you do not need to mirror it.Below are a few photos of the process.
Start and testWhen the board is assembled, you can proceed to the tests.We connect to the output a low-power load, for example, LED with a resistor and voltmeter for voltage monitoring. We supply voltage to the input and monitor the voltmeter readings, the voltage should change when the knob is rotated from minimum to maximum. The LED will change the brightness. If the voltage is regulated, then the circuit is assembled correctly, you can put the chip on the radiator and test it with a more powerful load. This adjustable stabilizer is ideal for use as a laboratory power supply. Particular attention should be paid to the choice of the chip, because it is very often forged. Fake chips are cheap, but they easily burn at 1 - 1.5 amps at a current. The original ones are more expensive, but they honestly provide the stated current up to 5 Amperes. Successful build.
Watch the videoThe video clearly shows the work of the stabilizer. When the variable resistor rotates, the voltage smoothly changes from minimum to maximum and vice versa, the LED changes brightness in this case.
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