Voltage stabilizer with short circuit protection, 14-16/9 volts. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Surge Protectors
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Many radio amateurs are familiar with the circuit of this simple voltage regulator with protection against overloads and short circuits of the output circuit. It has a number of positive qualities and therefore has gained wide popularity among radio amateurs. However, the disadvantage of the stabilizer is that the load current limiting threshold of its protection device depends on the static transfer coefficient of the regulating transistor. Since when the transistor heats up, its static current transfer coefficient increases, the stabilizer limiting current also increases. As a result, the power allocated to the regulating transistor increases, which can lead to its overheating and failure.
Diode V4, connected between the base of the control transistor and the collector of the control transistor (as shown in Fig. 1.15), practically eliminates this drawback.
In the normal mode of operation of the stabilizer, diode V5 is open, and diode V4 is closed and does not affect the operation of the device. If the load current is increased, then the output voltage of the stabilizer will begin to decrease, the diode V5 will close, and the transistor V2, together with the resistors R1, R3 and the zener diode V3, will work as a current stabilizer. In this regard, the base current of the regulating transistor V1, and hence its collector current, are limited.
Simultaneously with the closing of the diode V5, the diode V4 opens, shunts the zener diode V3, and it exits the stabilization mode. This leads to a decrease in the voltage at the base of the transistor V2 and, accordingly, to a decrease in the limiting current. If an LED, for example, AL4A, is used as a diode V102, then it will serve as an indicator of stabilizer overload, but in this case the short-circuit current of the stabilizer increases slightly due to a larger voltage drop at the LED junction.
Author: Semyan A.P.
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