Voltage stabilizing microcircuits of the KREN type (K142EN ...) are widely used in radio engineering, various household equipment. These microcircuits (MC) are available for various stabilization voltage values, among them there are adjustable options and with fixed output voltage values.
The load current of stabilization circuits on such MS is usually 1.5... 3 amperes.
In cases where the load requires much higher currents, such circuits are supplemented by a separate node on a powerful transistor, which is called "regulating". This transistor is controlled directly by the MC (in this case - KREN5A) and allows passing currents to the output of the stabilization device several times larger than the microcircuit itself can provide.
At the same time, all the main characteristics of the stabilizer as a whole, for example, the stabilization coefficient, remain at the level provided by the MS.
But the disadvantage of such circuits is that the current through the regulating transistor is not limited in any way and, if its values are too high, the transistor can be "broken". To prevent this from happening, you should somehow limit the maximum possible amount of current through the transistor. This can be done as shown in the diagram.
Parallel to the emitter junction VT1, two diodes D1, D2 are connected in series. If the load current exceeds 8 amperes, these diodes open, which triggers the internal (built-in) microcircuit overload protection system. The voltage at the output of the stabilizer will drop to zero and it will thus be “off” until the current drops below the permissible level (7-8 amperes).
The microcircuit itself, as well as the controlling powerful transistor, can be replaced with similar domestic or imported ones. They should be installed on heatsinks with sufficient cooling surface.
This scheme refers to the "simple" options and is not without, therefore, some disadvantages. For example, the value of the operating current of the protection system strongly depends on the parameters of the used transistors and diodes. But this drawback can be corrected by ensuring good thermal contact between their bodies.
To do this, you can fix the diodes directly on the heat sink of the transistor, while excluding electrical contact (use insulating gaskets made of mica or special heat-conducting gaskets).