LM317T safety application circuit

     When using LM317T to make an adjustable regulated power supply, poor contact of the potentiometer often causes the output voltage to rise and burn the load .

If a triode is added (as shown in the figure below), under normal circumstances, the base potential of T1 is 0 and T1 is turned off .

It has no effect on the circuit; when W1 has poor contact, the base potential of T1 rises. When it rises to 0.7V, T1 turns on .

Lowering the adjustment terminal voltage of LM317T will also lower the output voltage, thereby protecting the load. If removed

When the transistor is disconnected from the center point of W1, the small 3.8V bead burns out immediately, and the measured output voltage is as high as 21V. And add some

At T1, the brightness of the small beads decreases. At this time, the output voltage of LM317T is only 2V, thus effectively protecting the load.