Typical applications of several voltage regulators (TI) - LM317

The outstanding feature of the LM317 is that its output current can reach 1.5A, which provides more options for high loads. In addition, its output voltage adjustment range is also wide, 1.25-37V, and the chip has short-circuit current limiting and thermal overload protection. Only two resistors can be used to adjust the output voltage, which is very convenient to use.

Figure 1 Pin distribution diagram

The following discusses its typical applications:

Application 1:

Figure 2 Adjustable voltage calibrator

Ci is not necessary in the circuit diagram, but it is best to connect it to the circuit when it is far away from the adjustment. It can provide sufficient bypass current, especially when implementing voltage adjustment and connecting output capacitors. CO can provide a short response, which is not necessary for this circuit. The input voltage is calculated according to the following formula:

Among them, Iadj has little effect on the circuit because of its small current and can be ignored. Cadj can improve ripple suppression and limit the increase of ripple voltage when increasing the output voltage.

Application 2:

Figure 3 0-30V voltage adjustable circuit

The output voltage is as follows:

Likewise, Aadj can be ignored.

Application three:

Figure 4 Precision current limiting circuit

This circuit is very simple. It only needs to provide a feedback to ADJUST to control the output current by controlling the size of R1.

Application 4 (battery charging circuit):

Figure 5 Common battery charging circuit

The output impedance of this circuit depends on Rs, R1 and R2. The output impedance Z=Rs(1+R2/R1)

Figure 6 50mA constant current charger

Figure 7 Current-limited 6V charging circuit

This circuit sets the peak current through R3. When R3 is 1 ohm, the charging current can reach 0.6A.