Protection of the power unit against KZ

of the Fig. 1

the Circuit of connection of the transistor is provided by img src to the power unit on fig. 1, and volt-ampernye of the characteristic of the transistor for various resistance of the R1 resistor - on fig. 2. Protection so works. If resistance of the resistor equally to zero (i.e. the source is connected to a lock), and loading consumes a current about 0,25 And, power failure on the field transistor does not exceed 1,5 In, and practically on loading there will be all straightened tension. At emergence the current via the rectifier sharply increases in a chain of loading of KZ and in the absence of the transistor can reach several amperes. The transistor limits a current of short circuit at level 0,45... 0,5 And irrespective of power failure on it. In this case target tension becomes equal to zero, and all tension will fall on the field transistor. Thus, in case of KZ the capacity consumed from the power supply, will increase in this example no more than twice that is in most cases quite admissible and will not be reflected on "health" of details of the power unit.

of the Fig. 2

to Reduce a current of short circuit it is possible increase in resistance of the R1 resistor. It is necessary to choose such resistor that the current of short circuit was approximately twice more maximum current of loading. the Similar way of protection is especially convenient to br for power units with the smoothing RC filter - then the field transistor turn on instead of the filter resistor (such example is shown on fig. 3).
As during KZ on the field transistor falls almost all straightened tension, it can be used for the light or sound alarm system. Here, for example, the circuit of turning on of the light alarm system - fig. 7. When with loading everything is all right, the light-emitting diode of HL2 of green color burns. Thus on the transistor it is not enough power failure for ignition of a light-emitting diode of HL1. But it is necessary to appear KZ in loading as the light-emitting diode of HL2 dies away, but HL1 of a red luminescence flashes.

of the Fig. 3

the R2 Resistor choose img src by alt depending on the necessary restriction of a current of KZ according to the recommendations stated above. the Circuit of connection of a sound signaling device is provided by br on fig. 4. It can be connected or between a drain and a transistor source, or between a drain and a lock, as HL1 light-emitting diode.
At emergence on a signaling device of sufficient tension comes into effect the ZCh generator executed on the one-transitional VT2 transistor, and in a headphone of BF1 the sound is distributed.
the One-transitional transistor can be Kt117a-КТ117Г, phone - the low-impedance (it is possible to replace with a dynamic head of small capacity).

of the Fig. 4

Need to be added alt that for low-current loadings it is possible to enter the limiter of a current of KZ into the power unit on the field KP302V transistor. At a transistor choice for other blocks it is necessary to consider its admissible capacity and tension a drain - a source. Certainly, similar automatic equipment it is possible to enter br and into the stabilized power unit which does not have protection against KZ in loading.

I.NECHAEV, Kursk, Radio No. 7, 1989 of, p. 78

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