This stabilized power supply circuit may be directly linked to 230V AC mains to generate output voltages of 3V to 12V DC for connection to the prototyping board.

Step-down transformer X1 takes an input of 230 volts alternating current from the mains and converts it to 15 volts alternating current. The secondary winding of this transformer can carry a current of 2 amperes. The alternating current (AC) is changed into pulsating direct current (DC) by a bridge rectifier, which results in a peak voltage level of 21 volts (151.4142). When there is output available from the rectifier, LED1 will light up to signify this fact. The current that flows through LED1 is kept at a safe level below 10 milliamperes by the 2.2-kilohm resistor known as R1. Capacitor C1 with a value of 470 F helps to smooth out the output of the bridge rectifier. Bypassing the high frequency ripple is accomplished using capacitor C2. At the output of the rectifier section, a positive-voltage regulator from the LM317T series with three terminals is used for regulation. This regulator can be adjusted. It has the capability of supplying more than 1.5A across an output voltage range that goes from 1.2V to 37V. However, in this case it has been used to supply discrete voltages in steps of 3V, 5V, 6V, 9V, and 12V with the assistance of a 5-way rotary switch S2. This switch brings in different resistor values between the Adj pin of the regulator and ground, while R2 is a fixed resistor that has a value of 220 ohms and is located between the Adj pin and the output pin. The following equation can be used to get the voltage at the output (Vo): And 'Rx' denotes the resistance that may be found connected between the Adj pin of the regulator and ground. Rx has a value of 1900

ohms when it is set to the 12V position (the 'off' position of the switch), but when it is set to any of the other locations, it has a value that is the series equivalent of 1900 ohms when it is shunt with another resistance that is selected by the rotary switch. The rotary switch can be placed in any one of the locations shown in the table, which displays the equivalent series resistance in each position. Note The X1 rating in the circuit diagram has been printed in the wrong place. Therefore, 0-15V should be understood as the expression 15V-0-15V. Switching with a discrete resistor that has a tolerance of 1% is preferable to employing a variable resistor because, after some use, the wiper contact becomes erratic, and the tolerance (variation with temperature) of a variable resistor is also significantly higher. Discrete resistor switching is preferred.

In order to maximize the amount of heat that is transferred from the LM317T regulator to the PCB, a heat sink should be installed between the two components. It is important to keep in mind that the heat dissipated by the regulator will increase in proportion to the load current or the voltage drop across the load, whichever is greater. Assuming that you set the output to 3 volts and the load draws a current of 1.5 amps, the voltage drop across IC1 will be around 10 volts. The power that is lost at IC1 is equal to 10 times 1.5, which is 15 watts. You will need to make use of a heat sink that is approximately 4 by 10 centimeters in size in order to get rid of this heat. A plate of aluminum measuring the specified dimensions and measuring 3 millimeters thick and being screwed to the regulator will operate effectively. In order for adequate regulation to take place, there must be a voltage difference of at least 3 to 4 volts between the input and output voltages. In an ideal situation, the switch S1, transformer X1, LED1, fuse F1, and rotary switch S2 are all mounted appropriately in a box made of metal. After spreading some heat- sink paste on the area of LM317T that is made of metal, the heat-sink, which is an aluminum sheet, is to be fitted flat between the regulator and the PCB, and then it is to be attached using a nut and bolt. Make use of a rotary switch that is attached to the box, and then extend the connections from the PCB to the position of the rotary

switch. Ensure that the common connection is routed to the pole of the rotary switch. Because the LM317T contains built-in protection against short circuits, there is no need to place a fuse at its output. A correct PCB ought to be utilized in the wiring of the circuit.