Adjustable voltage stabilizing circuit that can automatically recover after a short circuit

(1)Circuit description

The circuit principle of the voltage regulator with automatic recovery function is shown in the figure below. When a short-circuit fault occurs in the load, the output current is not completely cut off, that is, a certain current continues to pass through the regulating tube. This current can make the voltage regulator automatically resume work after the fault is eliminated. However, since β has a great relationship with temperature, when the regulating tube is not completely open, it is easy to cause unstable short-circuit current and risk overloading the regulating tube.

In this regulator, the short-circuit current is determined by additional circuitry and is virtually independent of temperature. The associated circuit consisting of transistor VT1 protects the current from overload, and the associated circuit consisting of transistor VT2 determines the size of the short-circuit current.

(2) Working principle

When the output voltage increases, the base bias of transistor VT5 decreases, its collector current decreases, and the voltage increases, which causes the base voltage of transistor VT4 to increase, the current to decrease, and its emitter (i.e., the base of the adjustment tube VT3 (pole) The voltage increases, the current decreases, and the voltage drop Uce3 of the VT3 tube increases, which reduces the output voltage and achieves the purpose of voltage stabilization. The output voltage can be changed by adjusting potentiometer RP2.

When overload occurs, the voltage drop on resistor R3 increases, which reduces the base bias of the adjustment tube VT3, causing the protection tube VT1 to conduct slightly, the transistor VT5 to cut off, and the voltage regulator transitions to a working state that limits the load current. Adjust the potentiometer RP1 to determine the current limiting threshold. When the overload increases further, the load is cut off.

The automatic recovery circuit is determined by the transistor VT2 link. In a short circuit state, the tube is saturated and conductive, and the current passing through it is limited by resistor R1. When the load short-circuit fault is eliminated, a voltage appears that causes the transistor VT5 to conduct slightly, causing the voltage regulator to start.

The base voltage of transistor VT2 is pre-set by the voltage regulator diode VD1 to a level less than 5v, so that when the voltage regulator enters the working state, VT2 is cut off and the load current only passes through the regulating tube VT3.

(3)Installation instructions

During installation, in order to improve the thermal stability of the output voltage, the transistor VT5 and the zener diode VD2 should ensure good thermal contact. For example, they can be bonded together with epoxy resin, but there should be no electrical connection between the two. In order to ensure the thermal stability of the protection link. Transistor VT1 and adjustment tube VT3 should also have good thermal contact, and they can be installed on a heat sink.