The sound signaling device of an overload of the power supply unit. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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An audible alarm allows the user to quickly respond to an emergency if, during experiments with various equipment, an overload of the power source occurs. The power supply circuit with a sound stabilizer is shown in the figure.
(click to enlarge)
The rectifier on diodes VD1-VD4 is powered by a transformer, the secondary winding of which is designed for a voltage of 18 V at a current of at least 1A. The adjustable voltage regulator is made on transistors VT2-VT5 according to a well-known scheme.
Variable resistor R3 at the output can be set to a voltage from 0 to + 15V. The signaling device, designated as A1, is an audio frequency generator with an acoustic emitter connected to it (speaker, piezoelectric emitter, etc.). Its schematic diagram is not given, since the designer can choose a more acceptable "soundtrack" for him (tonal frequency, siren, multi-tone trill, melody, imitator of various sounds). The diagram of the device shows only the key that controls the operation of the signaling device on the transistor VT1.
The load current of the subject (device under test) passes through the resistor R2, creating a voltage drop across it. While the current is small (with the selected value of this resistor no more than 0,3A), transistor VT1 is closed. As the current consumption increases (and, accordingly, the voltage across the resistor increases), the transistor approaches the opening threshold.
When the voltage between the base and emitter VT1 reaches 0,7V, it opens and, with a further increase in current, goes into saturation.
When the transistor is opened, the rectified voltage is supplied to the acoustic signaling device and turns it on.
Transistors BC237 are interchangeable with KT639V, BC327 - with KT361B, BD283 - with KT815A. Instead of diodes 1N4001, rectifier diodes KD212B or bridge KTs405E are suitable. KS515A should be used as a zener diode. The power dissipation of the resistor R2 is taken with some margin, for example, 1W.
Publication: cxem.net
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