Economic signaling device for the presence of mains voltage. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power supply

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This signaling device is distinguished by its simplicity and, most importantly, its extremely low power consumption, since it operates in a pulsed mode. It is built according to the scheme shown in Fig. 1. Its main assembly, consisting of capacitors 01, 02 and diodes VD1, VD2, is similar in circuitry to a voltage doubling rectifier, differing from it in the capacitance values ​​of the capacitors.

Fig .1

Under the influence of the first negative half-cycle of the mains voltage, the capacitor 01 is charged through the diode VD1 to the amplitude value of this voltage, and in the next (positive) half-cycle, the mains voltage in total with the voltage on the charged capacitor 01 is applied to the diode VD1 in the opposite direction, and to the diode VD2 - in direct.

As a result, a portion of the charge of capacitor 01 is transferred to capacitor 02, the voltage across which increases by

where Um is the amplitude of the mains voltage. Approximately the same increment (it decreases as the capacitor 02 is charged), the voltage on it receives in each subsequent period of the mains voltage. As a result, the voltage applied to the anode-cathode gap of the VL1 thyratron increases stepwise, as shown in the graph in Fig. 2. For clarity, the graph is built for the capacitance of capacitor 01, which is several times larger than indicated in the diagram. Therefore, the height of the voltage steps on it is greater than in reality, and their number is less.

Fig. 2

The thyratron, since its control electrode is not connected anywhere, works in this device like a conventional neon lamp. Upon reaching the ignition voltage U, a gas discharge flashes in it and the capacitor 02 is quickly discharged by the current flowing through the resistor R1 and the anode-cathode gap of the thyratron, up to the discharge quenching voltage U,. Further, the charging of the capacitor is repeated, but starting from the Ur level. The flash repetition period T (in seconds) can be calculated using the formula

where F is the frequency of the supply voltage, Hz. Since the ratio equal to 1/T of the frequency of the discharge current pulses of the capacitor 02 to the frequency of the supply voltage remains constant when the latter changes, such devices were widely used as analog frequency dividers before the advent of digital microcircuits.

If desired, one or more LEDs can be connected in series with the thyratron EL1. They will all flash at the same time. It is only necessary to choose the resistor R1 so that the amplitude of the current pulses does not exceed the value allowed for the applied LEDs.

Author: R. Zakirov, Birsk, Bashkortostan; Publication: radioradar.net

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