Current limiting protection

The so-called current limiting protection means that once an overload or short circuit occurs in the output circuit of the voltage regulator, its output current will be limited to a certain value. In the series voltage regulator circuit shown in the figure, the resistor R and the diode BG₂ constitute a current limiting protection circuit. This protection circuit is suitable for the case where the forward voltage drop VBE1 of the emitter junction of the adjustment tube is lower than the forward voltage drop Vr of the diode. For example, the transistor uses a germanium tube, VBE:=0.2V, and BG₂ uses a silicon tube, Vp=0.7V. If the tubes of the same material are used, the number of diodes can be appropriately increased to meet the requirements.