Power management of an active TV antenna. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Television antennas

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Reducing electricity consumption during the operation of household appliances is an urgent task in modern conditions. Below is a fairly simple assembly that allows you to automatically achieve this when using active television antennas with modern televisions.

Active television antennas are widely used when the signal level is insufficient in different areas to provide better reception. During operation, users often do not provide for de-energizing the power supply of the antenna amplifier when the TV is turned off. However, calculations show that unjustified energy costs in this case are quite noticeable. Typically, the current consumed by the mentioned power supply is in the range of 20 ... 30 mA. With continuous operation of an active antenna, its energy consumption per month can be in the range of 3,2 ... 4,8 kWh. Therefore, turning off the power to the antenna amplifier at the same time when turning off the TV saves most of the indicated electricity.

A schematic diagram of a device that provides automatic switching on and off of the antenna amplifier is shown in the figure. The possibility of such a node connection is due to the fact that modern TVs can operate without degrading quality in a wide range of supply voltage values. Therefore, a slight decrease in the voltage supplied to the network input of the TV will be almost imperceptible.

Rice. Schematic diagram of a device that provides automatic switching on and off of the antenna amplifier

The device works very simply. When the TV is turned on, the mains current flows through the power supply circuit of itself and the primary winding of the current transformer T1 connected in series with it. The alternating voltage arising in its secondary winding is rectified by the diode bridge VD1 and smoothed out by the capacitor C1. The resulting DC voltage is supplied to the winding of the relay K1, which leads to its operation. Contacts K1.1 of the relay close and provide automatic supply of mains voltage to the power supply of the antenna amplifier. When the TV is turned off, the current through the transformer T1 and, therefore, through the winding of the relay K1 stops flowing. The contacts of relay K1.1 open, and the power supply of the antenna amplifier is automatically de-energized.

The calculation of the elements of the device can be carried out according to the proposed method. Of course, it is necessary to use a low-voltage low-power relay in it, which allows switching an alternating voltage of 220 V and a current of at least 30 mA.

The transformation ratio of transformer T1 is calculated by the formula N=P_t/(220I_k), where P_t - the power consumed by the TV; I_k - operating current of the relay winding. The operating voltage of the primary winding of the transformer is determined as follows: U \uXNUMXd I_kR_k/( 1,414N), where R_k - resistance of the relay winding.

Number of turns W₁ the primary winding of the transformer T1 for the calculated value of U is found by any known method, for example, as discussed in the book by Dyakonov V.P. "Handbook of calculations on microcalculators" (2nd ed. - M .: Nauka, 1986). The number of turns of the secondary winding is calculated by the formula W₂=W₁N.

In the implemented sample of the described device, designed for operation with a Sony Trinitron TV, the author used the RES55A reed relay and the TAG-II-2 transformer from the subscriber loudspeaker, the technical characteristics of which approximately correspond to the results of the calculation according to the proposed method.

The transformer is applied without rewinding. However, its secondary low-resistance winding is included in the network wire circuit of the TV, and the primary high-resistance winding is used to power the relay.

It should also be noted that the contacts of the RES55A reed relay of the required design, as indicated in the technical specifications, are designed for switching an alternating voltage of 127 V. However, the dielectric strength of the insulation of the contact leads in the KEM-3 reed switch, which is part of the relay, exceeds 200 V. Therefore, and also due to the fact that the power and current consumed by the antenna amplifier are not at all large, the author ventured to use this relay. And it works reliably. But even if, for some reason, a situation occurs when the reed switch contacts are constantly closed (“stick together”), this will only lead to the implementation of a continuous power supply mode for the antenna amplifier (without reducing power consumption). This mode does not pose a danger to either the TV or the antenna amplifier. Given the negligible power switched by the reed switch, the likelihood of such a situation occurring is small.

If radio amateurs wish to use the RES55A relay, we can recommend the execution of RS4.569 passports. 600-XX, where XX is 02-04, 07-11.

If the requirements for reliability are increased, you can use higher voltage products, for example, Cosmo reed relays with any passport data. It is only necessary to calculate the number of turns of the high-resistance winding of the transformer according to the specified method and apply the capacitor C1 to the rated voltage corresponding to the operating voltage of the relay. The transformer should be selected according to parameters close to the calculated data, or rewound with a significant difference in the number of turns in the windings.

In the case of using the RES55A relay, the operating voltage on its winding will be in the range of 3 ... 10 V, depending on the version. In this case, the voltage on the primary winding of the current transformer will not exceed 4 V, which does not lead to a noticeable decrease in the TV supply voltage.

Author: D. Onyshko

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