Basic circuit description of adjustable voltage regulator LM317

Knowledge about the adjustable voltage regulator LM317. The basic circuit of LM317 is as follows. C1 is the input capacitor, C2 is the output capacitor, and the LM317 voltage regulator block has a minimum stable operating current, which is called the minimum output current or minimum discharge current. Let's take a closer look.

Adjustable voltage regulator LM317 circuit

1. Basic circuit of LM317

The basic circuit of LM317 is as follows:

C1 is the input capacitor. When the front is connected to the rectifier and filter circuit and the distance between the voltage regulator and the rectifier and filter capacitor is less than 5~10CM, this capacitor can be omitted. The recommended value is 0.1μF.

C2 is the output capacitor, which improves transient response. The recommended value is 1μF.

2. Minimum stable operating current of LM317

The LM317 voltage regulator has a minimum stable operating current, which is called the minimum output current or the minimum discharge current.

The value of the minimum stable operating current is generally 1.5mA. Because the minimum stable operating current of the LM317 voltage regulator varies from manufacturer to manufacturer and from model to model, it is generally not greater than 5mA. When the output current of the LM317 voltage regulator is less than the minimum stable operating current, the LM317 voltage regulator cannot work properly.

When the output current of the LM317 voltage regulator block is greater than its minimum stable operating current, the LM317 voltage regulator block can output a stable DC voltage.

If you use the LM317 voltage regulator to make a regulated power supply (as shown in the figure), but do not pay attention to the minimum stable operating current of the LM317 voltage regulator, the regulated power supply you make may have abnormal phenomena: the loaded voltage and no-load voltage output by the regulated power supply will differ greatly.