Using LM317 to make a 1.5V adjustable power supply

Some electronic products use a single No. 7 battery. If you want to make an AC-to-DC power supply to replace the battery, you can use LM317 to achieve this goal.

The circuit schematic can refer to the circuit in the specification and can be modified according to the actual situation.

The basic principle is that after the AC 220 is transformed by the transformer, it is sent to the rectifier circuit. After high and low frequency filtering by two capacitors, a relatively flat DC voltage can be obtained. The choice of transformer can be flexibly selected according to the situation at hand, and it can generally be used in the range of 15 to 30V. The diodes at both ends of 317 are protective devices used for the circuit to generate reverse high voltage to prevent damage to the voltage regulator. The two power supplies form a regulation circuit. The adjustable resistor should be of a type with higher precision as much as possible, so that it will be more accurate when adjusting the voltage. The withstand voltage capacity of the capacitor should be more than twice the output voltage. It will be better if the capacitance and withstand voltage are larger. The voltage adjustment range of 317 is between 1.2 and 27V, so that a DC output of 1.5V can be achieved by adjusting the variable resistor. At present, switching power supplies are becoming more and more mature, but compared with linear power supplies, there are still some disadvantages, such as interference problems. In some occasions, linear power supplies still have advantages. It is still necessary to master some knowledge of linear power supplies.